Shock-induced damage beneath impact craters is studied in this work. Two representative terrestrial rocks, San Marcos granite and Bedford limestone, are chosen as test target. Impacts into the rock targets with different combinations of projectile material, size, impact angle, and impact velocity are carried out at cm scale in the laboratory.
Shock-induced damage and fracturing would cause large-scale compressional wave velocity reduction in the recovered target beneath the impact crater. The shock-induced damage is measured by mapping the compressional wave velocity reduction in the recovered target. A cm scale nondestructive tomography technique is developed for this purpose. This technique is proved to be effective in mapping the damage in San Marcos granite, and the inverted velocity profile is in very good agreement with the result from dicing method and cut open directly.
Both compressional velocity and attenuation are measured in three orthogonal directions on cubes prepared from one granite target impacted by a lead bullet at 1200 m/s. Anisotropy is observed from both results, but the attenuation seems to be a more useful parameter than acoustic velocity in studying orientation of cracks.
Our experiments indicate that the shock-induced damage is a function of impact conditions including projectile type and size, impact velocity, and target properties. Combined with other crater phenomena such as crater diameter, depth, ejecta, etc., shock-induced damage would be used as an important yet not well recognized constraint for impact history.
The shock-induced damage is also calculated numerically to be compared with the experiments for a few representative shots. The Johnson-Holmquist strength and failure model, initially developed for ceramics, is applied to geological materials. Strength is a complicated function of pressure, strain, strain rate, and damage. The JH model, coupled with a crack softening model, is used to describe both the inelastic response of rocks in the compressive field near the impact source and the tensile failure in the far field. The model parameters are determined either from direct static measurements, or from indirect numerical adjustment. The agreement between the simulation and experiment is very encouraging.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/0V4Q-VF61, author = {Stewart, Sarah Toby}, title = {Collisional Processes Involving Icy Bodies in the Solar System}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/0V4Q-VF61}, url = {https://resolver.caltech.edu/CaltechETD:etd-09242008-095607}, abstract = {
We present a complete description of the solid ice Hugoniot based on new shock wave experiments conducted at an initial temperature of 100 K and previously published data obtained at 263 K. We identify five regions on the solid ice Hugoniot: (1) elastic shock waves, (2) ice Ih deformation shocks, transformation shocks to (3) ice VI, (4) ice VII, and (5) liquid water. In each region, data obtained at different initial temperatures are described by a single Us - Δup shock equation of state. The dynamic strength of ice Ih is strongly dependent on temperature. The Hugoniot Elastic Limit varies from 0.05 to 0.62 GPa, as a function of temperature and peak shock stress. We estimate the entropy and temperature along the 100 and 263 K Hugoniots and derive the critical pressures for shock-induced incipient (IM) and complete (CM) melting upon release. On the 100 K Hugoniot, the critical pressures are about 4.5 and between 5-6 GPa for IM and CM, respectively. On the 263 K Hugoniot, the critical pressures are 0.6 and 3.7 GPa for IM and CM, lower than previously suggested. Shock-induced melting of ice will be widespread in impact events.
We present a model for the fluidization of Martian rampart crater ejecta blankets with liquid water based on the shock physics of cratering onto an ice-rich regolith. We conducted simulations of crater formation on Mars, explicitly accounting for the equations of state and shock-induced melting criteria for both the silicate and ice components and using strength models constrained by the observed transition diameter DTr from simple to complex craters on Mars, where DTr = 8 km corresponds to an effective yield strength of 107 Pa.
For the observed size range of rampart craters (diameters D ≾ 30 km) and typical asteroidal impact conditions (silicate impactors, D ≾ 1 km, at 10 km s-1), we find that the hemispherical volume where subsurface ice is partially melted by the impact shock has a radius of about 15 projectile radii (rp), much larger than previous predictions of about 6 rp. The radius of the final crater is comparable to the radius of partial melting and more than half the ice within the excavated material is melted. Thus, the amount of shock-melted water incorporated into the continuous ejecta blanket is within a factor of two of the near-surface ground ice content.
We find that fluidized ejecta blankets may form in the current climate with mean surface temperatures of 200 K. Decreasing the effective yield strength of the modeled materials, e.g., by increasing the ice content or porosity, modifies the impact-induced flow in the excavated cavity, resulting in deeper projectile penetration, steeper ejection angles, higher crater rim uplift, and reduced final crater diameter. The volume fraction of shock-melted water in the ejecta blanket increases with distance from the crater rim. The horizontal flow velocities during emplacement of fluidized ejecta (~ 10 - 1000 m s-1) is nearly constant in the continuous ejecta blanket and within the range of large terrestrial landslides. Therefore, ground-hugging debris flow conditions are achieved. The ejecta blanket properties from impacts into a Martian regolith containing 20-40%vol near-surface ice are consistent with the fraction of liquid water inferred from models of ejecta flow rheologies which produce rampart morphologies, about 10-30% liquid water by volume [Ivanov, B. A., Solar System Research, 30, 43-58, 1996].
We present a model for the formation of different rampart ejecta morphologies which may be used in conjunction with an ejecta blanket debris flow model to map the distribution of ground ice. In addition, we find that formation of single or multiple-rampart ejecta blankets does not require pre-existing liquid water in the Martian crust. We estimate the minimum water content in observed rampart ejecta blankets to be equivalent to a global layer of water 0.6 m thick. Based on the crater sampling efficiency, the implied global Martian ice content, within the upper 2 km of the crust, is equivalent to a global layer of water 100 m deep. This result is comparable to other estimates of HM2O content in the Martian crust.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/J8XC-TF53, author = {Ni, Sidao}, title = {2D Modeling of Lower Mantle Structure with WKM Synthetics}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/J8XC-TF53}, url = {https://resolver.caltech.edu/CaltechTHESIS:03252014-144322918}, abstract = {The Earth is very heterogeneous, especially in the region close to the surface of the Earth, and in regions close to the core-mantle boundary (CMB). The lowermost mantle (bottom 300km of the mantle) is the place for fast anomaly (3% faster S velocity than PREM, modeled from Scd), for slow anomaly (-3% slower S velocity than PREM, modeled from S,ScS), for extreme anomalous structure (ultra-low velocity zone, 30% lower inS velocity, 10% lower in P velocity). Strong anomaly with larger dimension is also observed beneath Africa and Pacific, originally modeled from travel time of S, SKS and ScS. Given the heterogeneous nature of the earth, more accurate approach (than travel time) has to be applied to study the details of various anomalous structures, and matching waveform with synthetic seismograms has proven effective in constraining the velocity structures. However, it is difficult to make synthetic seismograms in more than 1D cases where no exact analytical solution is possible. Numerical methods like finite difference or finite elements are too time consuming in modeling body waveforms. We developed a 2D synthetic algorithm, which is extended from 1D generalized ray theory (GRT), to make synthetic seismograms efficiently (each seismogram per minutes). This 2D algorithm is related to WKB approximation, but is based on different principles, it is thus named to be WKM, i.e., WKB modified. WKM has been applied to study the variation of fast D" structure beneath the Caribbean sea, to study the plume beneath Africa. WKM is also applied to study PKP precursors which is a very important seismic phase in modeling lower mantle heterogeneity. By matching WKM synthetic seismograms with various data, we discovered and confirmed that (a) The D" beneath Caribbean varies laterally, and the variation is best revealed with Scd+Sab beyond 88 degree where Sed overruns Sab. (b) The low velocity structure beneath Africa is about 1500 km in height, at least 1000km in width, and features 3% reduced S velocity. The low velocity structure is a combination of a relatively thin, low velocity layer (200 km thick or less) beneath the Atlantic, then rising very sharply into mid mantle towards Africa. (c) At the edges of this huge Africa low velocity structures, ULVZs are found by modeling the large separation between S and ScS beyond 100 degree. The ULVZ to the eastern boundary was discovered with SKPdS data, and later is confirmed by PKP precursor data. This is the first time that ULVZ is verified with distinct seismic phase.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J. and Helmberger, Donald V.}, } @phdthesis{10.7907/w8gc-n615, author = {Liu, Cangli}, title = {I. Rigid body penetration into brittle materials. II. Phase change effect on shock wave propagation}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/w8gc-n615}, url = {https://resolver.caltech.edu/CaltechTHESIS:04232013-084302487}, abstract = {Part I.
We have developed a technique for measuring the depth time history of rigid body penetration into brittle materials (hard rocks and concretes) under a deceleration of ~ 105 g. The technique includes bar-coded projectile, sabot-projectile separation, detection and recording systems. Because the technique can give very dense data on penetration depth time history, penetration velocity can be deduced. Error analysis shows that the technique has a small intrinsic error of ~ 3-4 % in time during penetration, and 0.3 to 0.7 mm in penetration depth. A series of 4140 steel projectile penetration into G-mixture mortar targets have been conducted using the Caltech 40 mm gas/ powder gun in the velocity range of 100 to 500 m/s.
We report, for the first time, the whole depth-time history of rigid body penetration into brittle materials (the G-mixture mortar) under 105 g deceleration. Based on the experimental results, including penetration depth time history, damage of recovered target and projectile materials and theoretical analysis, we find:
Part II.
Stress wave profiles in vitreous GeO2 were measured using piezoresistance gauges in the pressure range of 5 to 18 GPa under planar plate and spherical projectile impact. Experimental data show that the response of vitreous GeO2 to planar shock loading can be divided into three stages: (1) A ramp elastic precursor has peak amplitude of 4 GPa and peak particle velocity of 333 m/s. Wave velocity decreases from initial longitudinal elastic wave velocity of 3.5 km/s to 2.9 km/s at 4 GPa; (2) A ramp wave with amplitude of 2.11 GPa follows the precursor when peak loading pressure is 8.4 GPa. Wave velocity drops to the value below bulk wave velocity in this stage; (3) A shock wave achieving final shock state forms when peak pressure is > 6 GPa. The Hugoniot relation is D = 0.917 + 1.711u (km/s) using present data and the data of Jackson and Ahrens [1979] when shock wave pressure is between 6 and 40 GPa for ρ0 = 3.655 gj cm3 . Based on the present data, the phase change from 4-fold to 6-fold coordination of Ge+4 with O-2 in vitreous GeO2 occurs in the pressure range of 4 to 15 ± 1 GPa under planar shock loading. Comparison of the shock loading data for fused SiO2 to that on vitreous GeO2 demonstrates that transformation to the rutile structure in both media are similar. The Hugoniots of vitreous GeO2 and fused SiO2 are found to coincide approximately if pressure in fused SiO2 is scaled by the ratio of fused SiO2to vitreous GeO2 density. This result, as well as the same structure, provides the basis for considering vitreous Ge02 as an analogous material to fused SiO2 under shock loading. Experimental results from the spherical projectile impact demonstrate: (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. The supported elastic shock in vitreous GeO2 decays faster than a linear elastic wave; (2) In vitreous GeO2 , unsupported shock waves decays with peak pressure in the phase transition range (4-15 GPa) with propagation distance, x, as α 1/x-3.35 , close to the prediction of Chen et al. [1998]. Based on a simple analysis on spherical wave propagation, we find that the different decay rates of a spherical elastic wave in fused SiO2 and vitreous GeO2 is predictable on the base of the compressibility variation with stress under one-dimensional strain condition in the two materials.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J. and Stock, Joann M.}, } @phdthesis{10.7907/4dhf-fj83, author = {Winfree, Nancy A.}, title = {Impact-Induced Phase Transformations in Elastic Solids: A Continuum Study Including Numerical Simulations for GeO₂}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/4dhf-fj83}, url = {https://resolver.caltech.edu/CaltechETD:etd-02262008-153435}, abstract = {This thesis applies recently developed continuum theories of diffusionless phase transformations in solids to the study of impact problems involving materials which can experience such phase changes. Our objective is to compare the theoretical predictions against certain experimental results.
In the experiments of interest, a face-to-face impact occurs between a disk of amorphous germanium dioxide and another material, either tungsten or an aluminum alloy. The GeO₂ is believed to transform to another phase if sufficient compressive stress is achieved.
We model these experiments using one-dimensional finite elasticity. Phase-changing materials are represented by non-convex potential energy functions. This can produce phase boundaries that propagate subsonically or supersonically with respect to the slower longitudinal wave speed of the two phases. When a subsonic phase boundary is possible, it is not uniquely determined by the fundamental field equations and jump conditions. Uniqueness is obtained by invoking a nucleation criterion to control the initiation of the new phase, and a kinetic relation to govern its evolution.
The experiments considered here are sufficiently long in duration (≈ 3 µs) that several reflections and wave interactions occur, and the analysis becomes analytically intractable. Accordingly, a finite-difference method of Godunov type is employed to analyze these experiments numerically. Methods of Godunov type treat adjoining discretized spatial elements as the two sides of a Riemann problem, which is typically solved approximately by linearizing around the initial conditions on each side. Fortuitously, all constitutive models employed in this thesis are such that the required Riemann problems can be solved exactly without too much effort.
Simulations utilizing the numerical method demonstrate that the impact response of a material is sensitive to the kinetic relation that enters the model. It appears the theory may offer a plausible description of the experiments, though the restrictions placed on the constitutive models herein seem too severe to provide a good quantitative match to the experimental results.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Knowles, James K.}, } @phdthesis{10.7907/z7r2-xf47, author = {Chen, George (Guangqing)}, title = {I. High pressure melting of [gamma]-iron and the thermal profile in the Earth’s core. II. High pressure, high temperature equation of state of fayalite (Fe2SiO4)}, school = {California Institute of Technology}, year = {1998}, doi = {10.7907/z7r2-xf47}, url = {https://resolver.caltech.edu/CaltechETD:etd-02262007-141751}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
The melting curve of […]-iron in the pressure range of 100 to 300 GPa has been derived by computing Gibbs free energies at high pressures and high temperatures from thermodynamic and equations of state (EOS) data for the […], […] and liquid-phases. Our calculations indicate the melting curve of iron is very sensitive to the EOS of both the solid […] and melt phase. Our best estimate of the EOS parameters for […]-iron are: p0 = 8.775 ± 0.012 Mg/m3, […] = 205 ± 4 GPa, […] = 4.80 ± 0.01 (referenced to 12 GPa and 300 K). The calculation favors the melting curve of Boehler [1993] or Saxena et al. [1993]. Shock-wave experiments on pure iron preheated to 1573 K were conducted in 17-73 GPa range. The shock-wave equation of state of [gamma]-iron at 1573 K initial temperature can be fit with […] = 4.102(0.015) km/s + 1.610(0.014)[…] with […] = 7.413 ± 0.012 Mg/m3. [Gamma]-iron’s bulk modulus and its pressure derivative are 124.7±1.1 GPa and 5.44±0.06 respectively.
We present new data for sound velocities in the [gamma]- and liquid-phases. In the [gamma]-phase, to a first approximation, the longitudinal sound velocity is linear with respect to density: Vp = -3.13(0.72) + 1.119(0.084) […] (units for Vp and […] are km/s and Mg/m3 respectively). Melting was observed in the highest pressure (about 70-73 GPa) experiments at a calculated shock temperature of about 2775 ± 160 K. This result is consistent with our calculated […]-iron melting curve which is close to those measured by Boehler [1993] and Saxena et al. [1993]. The liquid iron sound velocity data yield a Gruneisen parameter value for liquid iron of 1.63±0.28 at 9.37±0.02 Mg/m3 at 71.6 GPa. The quantity […] from our data is 15.2±2.6 Mg/m3, which is within the bounds of Brown and McQueen [1986] (13.3-19.6 Mg/m3). Based on upward pressure and temperature extrapolation of our melting curve of [gamma]-iron, the estimated inner core-outer core boundary temperature is 5500±400 K, the temperature at the core-mantle boundary on the outer core side is about 3930±630 K, and the thermal boundary layer at the core-mantle boundary has a temperature difference between 400 and 1400 K.
The shock-wave equation of state of initially solid (300 K) and molten (1573 K) fayalite (Fe2SiO4, Fa) are reported in the ranges 23 to 212 GPa and 5 to 47 GPa, respectively. The 300 K data appear to undergo a phase change in the 35-55 GPa range. The density of the high pressure phase (HPP) is consistent with a dense oxide mixture. Although the initially 300 K fayalite may melt along its Hugoniot, this is not explicitly detected. Fitting the HPP Hugoniot data in the shock velocity ([…])-particle velocity ([…]) plane yields:
[…] = 4.375(0.027) Mg/m3, (1)
[…] = 4.07(0.22) km/s + 1.43(0.06) […], (2)
where […] is the initial density. The isentropic bulk modulus […] = 72.4 ± 8.0 GPa, and its pressure derivative […] = 4.72±0.24.
The 1573 K data set yields:
[…] = 3.750(0.018) Mg/m3, (3)
[…] = 2.63(0.02) km/s + 1.59(0.01) […], (4)
and […] = 25.9 ± 0.4 GPa, […] = 5.36 ± 0.04. The bulk modulus compares favorably with Agee [1992a]’s result (24.4 GPa), but the pressure derivative is quite different (10.1 from Agee [1992a]).
Above 50 GPa, the high pressure regime of the Hugoniot of the solid fayalite can be fit with oxide mixture models using stishovite and FeO (either LPP or HPP). The fayalitic liquid compression data above 40 GPa are well fit with ideal mixing of partial molar volumes of stishovite and FeO (LPP or HPP), in support of the hypothesis of Rigden et al. [1989].
A model basalt incorporating the liquid fayalite data shows the neutral buoyancy zone of basic silicate melts of plausible terrestrial compositions is at about 250-400 km depth based on the PREM Earth model.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/2jtf-x438, author = {Takata, Toshiko}, title = {Three-dimensional analysis of impact processes on planets}, school = {California Institute of Technology}, year = {1995}, doi = {10.7907/2jtf-x438}, url = {https://resolver.caltech.edu/CaltechETD:etd-11012007-084634}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
This thesis consists of four chapters. The first chapter describes the numerical method known as Smoothed Particle Hydrodynamics (SPH), that is used in present calculations relating to oblique impact on a planet with an atmosphere. Numerical test results are presented to demonstrate the validity of the present computer code. The SPH code is applied to Comet Shoemaker-Levy 9 impact on Jupiter, particularly the disintegration of the comet in the Jovian atmosphere and the evolution of the vapor plume. These calculations are described in chapter II. In order to interpret the phenomena observed in the impacts, numerical predictions are compared with the observational data. These comparisons are summarized in chapter III. Chapter IV considers analytical models of the formation of radar dark and/or bright halos surrounding impact craters discovered on Venus as a result of the Magellan mission. The surface features caused by the atmospheric shock waves associated with impacts are modeled and applied to the observed Venusian radar features.
Paper I:
The SPH method used for a series of impact calculations is tested. From the performance tests, we infer that the tree structure method for a vectorizing computer code can be applied when the number of particles, N, […]. Most of the calculations are performed using a CRAY-YMP at Jet Propulsion Laboratory or a CRAY-C90 at Goddard Space Flight Center. Tests for one-dimensional shock propagation show that the developed code yields an error of less than several percent in density and pressure, upon comparison with the analytical impedance-match solution. For spherical, three-dimensional impact of a projectile upon a silicate half-space, the shock wave attenuation of pressure and density calculated by the SPH code is very similar to the results obtained with a finite-difference Lagrangian continuum code (previously obtained by Ahrens and O’Keefe, [1977]). For example, the shock pressures in the near field agree within 15 % differences, whereas the shock pressure in the far field, at 10 projectile radii, differs by a factor of 2 from that calculated previously using a two-dimensional axisymmetric Lagrangian code.
Paper II:
The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion are investigated by conducting three-dimensional numerical simulations using the Smoothed Particle Hydrodynamics (SPH) method. An icy body, representing the cometary fragments, with a velocity of 60 km/sec and a diameter of 2 km can penetrate to 350 km below the 1-bar pressure level in the atmosphere. Most of the initial kinetic energy of the fragment is transferred to the atmosphere between 50 km and 300 km below the 1-bar pressure level. The shock-heated atmospheric gas in the wake is totally dissociated and partially ionized. Scaling our SPH results to other sizes indicates that fragments larger than […] 100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explosively released in the upward expansion of the resulting plume. The plume preferentially expands upward rather than horizontally due to the density gradient of the ambient atmosphere. It rises …] km in […] seconds. Eventually the total atmospheric mass ejected to above 1 bar is […] 40 times the initial mass of the impactor. The plume temperature at a radius ~ […] km is > […] K for […] seconds, for a 2-km fragment. We predict that impact-induced plumes will be observable with the remote sensing instruments of the Galileo spacecraft. As the impact site rotates into the view of the earth some 20 minutes after the impact, the plume expansion will be observable using the Hubble Space Telescope and from visible and infrared instruments on ground-based telescopes. The rising plume reaches ~ 3000 km altitude in ~ ten minutes and will be visible from the earth.
Paper III:
Preliminary observational data from the impact of fragments of Comet Shoemaker-Levy 9 (SL9) are compared with smoothed particle hydrodynamic (SPH) and radiative calculations to determine the energies of individual SL9 fragments and the equivalent diameter of the SL9 progenitor. The Hubble Space Telescope (HST) images of the G impact-induced plume demonstrate that it achieved a height of ~3300 km [Hammel et al., 1994]. This is in close agreement with the SPH calculations for a 7 x […] erg or 2 km ± 0.3 km diameter solid ice impactor at 60 km/sec. Comparison of the R fragment impact-induced plume brightness in the 8 to 12 […] band, as recorded by the NASA Infrared Telescope Facility (Mauna Kea, HI) [Orton et al. 1994], with our radiative predictive calculations yields a kinetic energy of 4 x […] ergs or a diameter of 1.6 ± 0.3 for the R fragment. Using the G and R impacts to calibrate Weaver et al.’s [1994] detailed photometric determination of the relative diameters of pre-Jovian impact projectiles in the SL9 chain from HST images yields revised values for the 11 largest fragment diameters. Adding the inferred masses from the plume and radiative calibration of Weaver et al.’s catalog yields an SL9 progenitor equivalent (ice) diameter of 4.1 ± 0.6 and 3.5 ± 0.5 km, respectively. This compares to a 7.7 km diameter progenitor inferred by Weaver et al. and a 2 km diameter progenitor obtained using tidal break-up modeling by Scotti and Melosh [1993] and Asphaug and Benz [1994]. We also examined the inferred position of Jupiter derived H2O impact ejecta from the hypothetical (3 to 5 bar) cloud deck and find that although Jupiter derived impact induced plumes having radius of > […] km and achieved altitudes of 3 x […] km, the contained Jovian water ejecta is restricted to the interior of the plume and would be masked from Earth observations by the surprisingly opaque plume. On the basis of Bjorker et al.’s [1994] observations of thirty minutes’ water emissions from the plumes of the impact sites of fragments G and K Field and Ferraro’s [1994] analysis which indicates that even if SL9 fragments are 50% porous, upon being subjected to entry, the ram pressures, upon reaching the level of 1 bar, squeeze-out virtually all porosity and the present, self-consistent kinemetric and radiative coupling of the SL9 impactor, we conclude: 1) there is no evidence that SL9 was anything but a comet as first suggested by the coma, 2) penetration of 2 km diameter fragments occurs to depths of ~ 300 km, even for a porous comet, as calculated by the present SPH method and by other groups using finite difference methods [Zahnle and MacLow, 1993, Boslough et al., 1994].
Paper IV:
A paraboloidal bow shock model was developed in order to estimate the surface distribution of gas shock-induced modifications surrounding venusian impact craters. We applied two-dimensional oblique shock dynamics to describe a three-dimensional paraboloidal - shaped bow shock impinging upon an assumed incompressible venusian surface. The effects of the hypersonic atmospheric shock acting on the venusian surface are considered in terms of maximum gas pressure, the density, the particle velocity, and the temperature, for varying angles and velocities of impact. The maximum boulder size that can be saltated by the shockwave induced gas flow and the degree of mutual collision of the surface materials are also considered. The present calculations quantitatively predict the areal extent of the gas shock perturbed surface for normal and oblique impact as a function of impact angle and velocity, and radii of impactors. For a 1 km-radius stony meteorite impacting at 20 km/s, the radius of the disturbed area extends ~ 10-17 times the 3-5 km crater radius. The perturbed surface affects the surface radar properties and the present results can provide an explanation of the wide “dark/bright halos” surrounding some of venusian impact craters observed via Magellan imagery. For example, a ~ 50 km radius bright halo within a ~ 20 km dark halo is observed around the 3.1 km-radius crater located at 16.5° north latitude and 334.4° longitude. The average value of the radar backscatter cross section of the ~ 20 km radius dark halo indicates that ~ 50 cm-thick layer of porous lithologic material is superimposed upon the undisturbed surface. The occurrence of the bright halo indicates that the surface roughness in this region is ~ 30% greater than that of the surrounding original surface. The present model can relate the observed crater halo radii to the impact parameters, such as impact velocity and angle, and the impactor radius.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/J6D0-GV56, author = {Rowan, Linda Rose}, title = {Equation of state of molten mid-ocean ridge basalt. Structure of Kilauea volcano.}, school = {California Institute of Technology}, year = {1993}, doi = {10.7907/J6D0-GV56}, url = {https://resolver.caltech.edu/CaltechTHESIS:01142013-104747074}, abstract = {Basalts are the most ubiquitous rocks erupting at the earth’s surface at the present time and they provide an important probe of the subsurface processes occurring within planetary interiors. Recent advances in both mineral physics and seismic analysis have allowed me to undertake two independent studies related to the genesis and eruption of basaltic magmas. Chapters 1 and 2 are part of an experimental study conducted in the shock wave laboratory on the equation of state of molten mid-ocean ridge basalt and the chemical interactions of the shocked liquid with its Mo container. My advisors for this project were Thomas Ahrens and Edward Stolper. Chapter 3 is a travel time tomography study of the three-dimensional structure of Kilauea Volcano, Hawaii in collaboration with Robert Clayton. Chapter 3 is currently in press in the Journal of Geophysical Research.
The EOS of molten MORB to 20 GPa was accomplished using the innovative silicate liquid shock wave measurement technique on the 40 mm propellant gun developed by Rigden [1986] and Miller [1990). This technique has been used to determine the EOS for four synthetic melts and this thesis applies the technique to a natural melt, a MORB dredged from the Juan de Fuca ridge. The resulting EOS indicates that the MORB liquid is very compressible and therefore has a low bulk modulus of 11.7 GPa. These results are consistent with low pressure static compression experiments on similar basalts, but are not consistent with the results of ultrasonic interferometry. The compressible nature of the MORB liquid is related to its composition and this may be expressed best by comparing the MORB Hugoniot to the Hugoniot determined for An_(36)Di_(64) and komatiite. The MORB and An_(36)Di_(64) Hugoniots show significant increase in density at low pressure followed by a stiffening at high pressures where the liquid Hugoniot approaches its respective dense oxide high pressure composition. This may be related to gradual coordination changes from four-fold to six-fold for the Si^(+4) and Al^(+3) which are essentially complete at the high pressure where the curve stiffens. The MORB is much more compressible than the komatiite and overtakes the komatiite in density at a low pressure of 2.5 GPa. This is a compositional effect caused by the enrichment of the MORB in Al_2O_3 and SiO_2 and depletion in MgO compared to komatiite. The compressible nature of the MORB allows it to become denser than the surrounding mantle near the base of the low velocity zone and therefore it is unlikely that MORB can be derived from very deep in the earth’s upper mantle.
For most shock wave experiments, the sample is not recovered and nothing can be determined about its structure or composition due to the passage of the shock wave. In a few of my EOS experiments on molten MORB, however, the shocked sample was recovered and could be studied in detail. Observations of impact-induced interactions between the silicate liquid and its Mo container provide insight into planetary impact and differentiation processes involving metal-silicate partitioning. The shocked liquids showed extreme reduction and with increasing pressure the FeO content of the initial melt was reduced to almost nothing by reaction with the Mo. These reactions produced metallic particles enriched in Mo, Fe and Si. These particles show a similar texture as those found at impact sites on the earth and moon and provide clues to the impact origin of metallic particles.
A travel time tomography study of local P wave data from Kilauea Volcano, Hawaii, was undertaken to determine the lateral heterogeneities produced by its intricate magmatic and tectonic environment. The technique proved to be a powerful probe of the volcano’s intrusive plumbing because the presence of a dense seismic array and many local earthquakes allowed for excellent coverage of complex subsurface features. Analysis and interpretation of the tomographic images leads to the following inferrred model. The main shallow magma reservoir is delineated by a slow anomaly centered 2 km southeast of Halemaumau caldera. There is a distinct high velocity region centered northwest of the summit from 0 to 2 km depth that may represent a dense wall and/or cap of intrusive rock that acts as a barrier or containment structure for the northern part of the reservoir. We suggest that the shallow reservoir is a narrow, compartmentalized region of sills and dikes because of the closely spaced high and low velocity anomalies near the summit. The rift zones of Kilauea are imaged as major, high velocity entities, widening to the south with depth until 6 km. These fast anomalies may be related to the sheeted dike complexes along the rifts. On a finer scale, magma pockets centered at 0-2 km depth have been inferred beneath Makaopuhi, Mauna Ulu and Puu Oo, along the east rift zone. The Hilina and Kaoiki fault zones, are imaged as slow features at shallow depths (less than 6 km), related to their tensional structures that produce the open fractures and cracks in the basaltic edifice. The Koae fault system is imaged as a slightly fast shallow structure (less than 6 km) possibly related to intrusive diking from the adjacent rift zones. Continued inversions with the immense amount of seismic data collected for Hawaiian events will allow the detailed development of a three-dimensional velocity model for Kilauea. Such a model will be extremely useful to seismologists and petrologists alike for understanding the tectonic growth and magmatic evolution of this dynamic shield volcano.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J. and Stolper, Edward M. and Clayton, Robert W.}, } @phdthesis{10.7907/m63k-zj81, author = {Duffy, Thomas Sheehan}, title = {Elastic Properties of Metals and Minerals under Shock Compression}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/m63k-zj81}, url = {https://resolver.caltech.edu/CaltechETD:etd-05172007-104609}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
Comparison of laboratory elasticity data with seismic measurements of the Earth provides a means to understand the deep interior. The effect of pressure and temperature on elastic properties must be well understood for meaningful comparisons. In this work, elastic wave velocities have been measured under shock compression to 80 GPa in an Fe-Cr-Ni alloy, to 27 GPa in polycrystalline MgO, and to 81 GPa in molybdenum preheated to 1400°C. These measurements were made by recording particle velocity histories at a sample surface using the method of velocity interferometry. In addition to elastic properties, these experiments provide information on the constitutive and equation of state (EOS) properties of the sample as well as the unloading adiabats.
Compressional and bulk wave velocities in Fe-Cr-Ni alloy are consistent with third-order finite strain theory and ultrasonic data. Thermal effects on the wave velocities are less than 2% at 80 GPa. Second pressure derivatives of velocity were constrained along the Hugoniot to be: (∂2CL/∂P2)H = -0.16 (0.06) GPa-1 and (∂2KS/∂P2)H = -0.17 (0.08) GPa-1. The measured wave profiles can be successfully reproduced by numerical simulations utilizing elastic-plastic theory modified by a Bauschinger effect and stress relaxation. Material strength was found to increase by a factor of at least 5 up to 80 GPa and to be 2-3% of the total stress.
Compressional and bulk velocities in Fe-Cr-Ni define linear velocity-density trends and can be modeled by averaging properties of Fe, Cr, and Ni. The effect of alloying ~4 wt.% Ni with Fe would change both VP and VB by less than 1% under core conditions. Compressional velocities in Fe-Ni are compatible with inner core values when corrected for thermal effects. Shear velocities in Fe, determined from a combination of VP and VB data, are ~3.6 km/s at P=150-200 GPa. Low values are most likely caused by a weak pressure dependence of the rigidity and imply that partial melting is not required in the inner core.
Wave profile and EOS measurements in polycrystalline MgO define its EOS: US = 6.77(0.08) + 1.27(0.04)up. Compressional sound velocities to 27 GPa yield the longitudinal modulus and its pressure derivative: CLo = KoS + 4/3G = 335 ± 1 GPa and C’Lo = 7.4 ± 0.2, which are in good agreement with ultrasonic determinations. The unloading wave profiles can be modeled using a modified elastic-plastic constitutive response originally developed for metals. Thermal expansivities in MgO have been determined to be 12 ± 4 x 10-6 K-1 at P=174-200 GPa and T=3100-3600 K from shock temperature and EOS data. These results imply that the lower mantle is enriched in Si and/or Fe relative to the upper mantle.
Wave profiles in molybdenum at 1400°C are the first wave profile determinations at significantly high initial temperature. The EOS determined from these measurements agrees well with previous data. The compressive yield strength of Mo is 0.79-0.94 GPa at 1400°C, and the HEL stress is 1.5-1.7 GPa. The temperature coefficient of compressional velocity, (∂Vp/∂T)p, is found to vary from -0.35(0.13) m/s/K at 12 GPa to -0.18(0.14) m/s/K at 81 GPa and compares with an ambient pressure value of -0.26 m/s/K. It is inferred that (∂Vp/∂T)p decreases with pressure, and data for Mo are shown to be consistent with trends defined by other metals.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/thvj-vd30, author = {Zhao, Lian-She}, title = {Seismic waveform modeling of regional phases and wavefields from an off-center explosion}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/thvj-vd30}, url = {https://resolver.caltech.edu/CaltechTHESIS:10032011-142032525}, abstract = {This thesis consists of two parts. Part I (Chapter 1) is a theoretical study of wavefields radiated from an off-center explosion in an embedded solid sphere, while Part II (Chapters 2, 3 and 4) deals with seismic waveform modeling of regional phases.
Chapter 1 investigates the effects of asymmetric source regions on the excitation of seismic body waves of explosions. We give an analytic formulation for determining the wave fields from an off-center explosion in an embedded solid sphere in an elastic whole-space. It is shown that SH wave amplitudes can be ten times larger than the P wave amplitudes if the source is properly located.
Chapter 2 discusses the strategies of modeling regional Broadband recordings with the application to Harvard station recordings of November 25, 1988 Saguenay earthquake. We demonstrate that the longer period motions (WWSSN) preceding the direct S arrival can be modeled reasonably well with a crustal model consisting of a layer over half-space. While a generic model assumed to be the same everywhere can be used to model the P_nl waveshape, HeImberger and Engen (1980), some adjustments are required to fit the absolute timing of P_n and S_n for specific paths. In particular, path from the Saguenay event to Harvard is slower than expected for a shield environment and is associated with the roots of the Appalachian Thrust Belt.
Chapters 3 and 4 concern the velocity structures of the Tibetan Plateau and surrounding regions. A fast shield-like velocity model, TIP, is proposed for the structure beneath the Tibetan Plateau as suggested by modeling SH waveforms in Chapter 3. The crustal model is determined by modeling Love waveforms and P_nl waveforms in the time domain while the upper mantle is constrained with S and SS waveform data. Relocations of Tibetan earthquakes are discussed in Chapter 4, assuming model TIP at source region and model JB at receiver regions. A detailed investigation of 100 such events yields a distinctly different picture from a random distribution of events down to a depth of about 50 kms given by ISC. Waveform modeling of depth phases such as _pP indicates that only three or four events from of this population is actually deeper than 25 km. These few events occur near the edges of the Plateau where active subduction is occurring as suggested by the thrust-like nature of their mechanisms. The events occurred earlier than indicated by the ISC by 3 seconds on average which leads to about a 1.5% and 0.5% over estimation of P_n and S_n velocities respectively applying ISC tables and standard flat-layered models.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/49fn-dg49, author = {Smither, Catherine Louise}, title = {Stress-relief displacements induced by drilling and three-dimensional modeling of planetary impacts}, school = {California Institute of Technology}, year = {1992}, doi = {10.7907/49fn-dg49}, url = {https://resolver.caltech.edu/CaltechTHESIS:09282011-151807180}, abstract = {The holographic stressmeter uses double-exposure holographic interferometry to record the displacements induced by the drilling of a sidehole into the borehole wall. The local stresses, which are the result of the far-field stresses, concentrated at the borehole, cause deformation of the surface of the borehole wall near the sidehole. To interpret the data, it is essential to understand this deformation. The initial model used a thin infinite elastic plate subjected to plane stress at infinity. Two-dimensional finite element analysis showed that the displacement depends on the depth of the sidehole. We then developed a new model for the analysis of stress-relief displacements. For holes with a depth/diameter ratio greater than unity, the simple plane stress elastic plate solution breaks down. The revised model, which gives a more exact solution of displacements near the hole, does a better job of fitting the observed data.
A three-dimensional smoothed particle hydrodynamics code was used to model normal and oblique impacts of silicate projectiles on planetary bodies. The energy of the system is partitioned after impact into internal and kinetic energy of the both bodies. These simulations show that, unlike the case of impacts onto a half-space, up to 70% of the initial energy remains in the kinetic energy of the impactor, as parts of it travel past the main planet and escape the system. More oblique impacts retain more kinetic energy in the impactor: 6 to 75% versus 4 to 30% for the normal impacts. Higher velocity collisions also show this trend, as the kinetic energy of the impactor is 2 to 50% of the total for 5 km/s impacts, and 13 to 75% for 20 km/s impacts. Impacts at 20 km/s with an impactor 60% the size of the target completely melted both targets. Three to 4 times more vaporization of the target material occurred on the larger targets. The amount of target material ejected at velocities greater than the escape velocity is found to be higher than that predicted by studies of impact onto a half-space, and slightly less than the amount predicted by theories of catastrophic breakup of asteroids.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/7dsx-ed25, author = {Anderson, William Wyatt}, title = {High pressure states in condensed matter: I. High pressure behavior of the iron-sulfur system with applications to the earth’s core. II. Empirical equation of state for organic compounds at high pressures}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/7dsx-ed25}, url = {https://resolver.caltech.edu/CaltechTHESIS:03182015-092735941}, abstract = {Part I:
The earth’s core is generally accepted to be composed primarily of iron, with an admixture of other elements. Because the outer core is observed not to transmit shear waves at seismic frequencies, it is known to be liquid or primarily liquid. A new equation of state is presented for liquid iron, in the form of parameters for the 4th order Birch-Murnaghan and Mie-Grüneisen equations of state. The parameters were constrained by a set of values for numerous properties compiled from the literature. A detailed theoretical model is used to constrain the P-T behavior of the heat capacity, based on recent advances in the understanding of the interatomic potentials for transition metals. At the reference pressure of 105 Pa and temperature of 1811 K (the normal melting point of Fe), the parameters are: ρ = 7037 kg/m3, KS0 = 110 GPa, KS’ = 4.53, KS" = -.0337 GPa-1, and γ = 2.8, with γ α ρ-1.17. Comparison of the properties predicted by this model with the earth model PREM indicates that the outer core is 8 to 10 % less dense than pure liquid Fe at the same conditions. The inner core is also found to be 3 to 5% less dense than pure liquid Fe, supporting the idea of a partially molten inner core. The density deficit of the outer core implies that the elements dissolved in the liquid Fe are predominantly of lower atomic weight than Fe. Of the candidate light elements favored by researchers, only sulfur readily dissolves into Fe at low pressure, which means that this element was almost certainly concentrated in the core at early times. New melting data are presented for FeS and FeS2 which indicate that the FeS2 is the S-hearing liquidus solid phase at inner core pressures. Consideration of the requirement that the inner core boundary be observable by seismological means and the freezing behavior of solutions leads to the possibility that the outer core may contain a significant fraction of solid material. It is found that convection in the outer core is not hindered if the solid particles are entrained in the fluid flow. This model for a core of Fe and S admits temperatures in the range 3450K to 4200K at the top of the core. An all liquid Fe-S outer core would require a temperature of about 4900 K at the top of the core.
Part II.
The abundance of uses for organic compounds in the modern world results in many applications in which these materials are subjected to high pressures. This leads to the desire to be able to describe the behavior of these materials under such conditions. Unfortunately, the number of compounds is much greater than the number of experimental data available for many of the important properties. In the past, one approach that has worked well is the calculation of appropriate properties by summing the contributions from the organic functional groups making up molecules of the compounds in question. A new set of group contributions for the molar volume, volume thermal expansivity, heat capacity, and the Rao function is presented for functional groups containing C, H, and O. This set is, in most cases, limited in application to low molecular liquids. A new technique for the calculation of the pressure derivative of the bulk modulus is also presented. Comparison with data indicates that the presented technique works very well for most low molecular hydrocarbon liquids and somewhat less well for oxygen-bearing compounds. A similar comparison of previous results for polymers indicates that the existing tabulations of group contributions for this class of materials is in need of revision. There is also evidence that the Rao function contributions for polymers and low molecular compounds are somewhat different.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/r0pt-2227, author = {Miller, Gregory Hale}, title = {The Equation of State and Petrogenesis of Komatiite}, school = {California Institute of Technology}, year = {1990}, doi = {10.7907/r0pt-2227}, url = {https://resolver.caltech.edu/CaltechTHESIS:03272015-161328191}, abstract = {
The equation of state (EOS) of a molten komatiite (27 wt% MgO) was detennined in the 5 to 36 GPa pressure range via shock wave compression from 1550°C and 0 bar. Shock wave velocity, US, and particle velocity, UP, in km/s follow the linear relationship US = 3.13(±0.03) + 1.47(±0.03) UP. Based on a calculated density at 1550°C, 0 bar of 2.745±0.005 glee, this US-UP relationship gives the isentropic bulk modulus KS = 27.0 ± 0.6 GPa, and its first and second isentropic pressure derivatives, K’S = 4.9 ± 0.1 and K"S = -0.109 ± 0.003 GPa-1.
The calculated liquidus compression curve agrees within error with the static compression results of Agee and Walker [1988a] to 6 GPa. We detennine that olivine (FO94) will be neutrally buoyant in komatiitic melt of the composition we studied near 8.2 GPa. Clinopyroxene would also be neutrally buoyant near this pressure. Liquidus garnet-majorite may be less dense than this komatiitic liquid in the 20-24 GPa interval, however pyropic-garnet and perovskite phases are denser than this komatiitic liquid in their respective liquidus pressure intervals to 36 GPa. Liquidus perovskite may be neutrally buoyant near 70 GPa.
At 40 GPa, the density of shock-compressed molten komatiite would be approximately equal to the calculated density of an equivalent mixture of dense solid oxide components. This observation supports the model of Rigden et al. [1989] for compressibilities of liquid oxide components. Using their theoretical EOS for liquid forsterite and fayalite, we calculate the densities of a spectrum of melts from basaltic through peridotitic that are related to the experimentally studied komatiitic liquid by addition or subtraction of olivine. At low pressure, olivine fractionation lowers the density of basic magmas, but above 14 GPa this trend is reversed. All of these basic to ultrabasic liquids are predicted to have similar densities at 14 GPa, and this density is approximately equal to the bulk (PREM) mantle. This suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km.
The EOS of ultrabasic magmas was used to model adiabatic melting in a peridotitic mantle. If komatiites are formed by >15% partial melting of a peridotitic mantle, then komatiites generated by adiabatic melting come from source regions in the lower transition zone (≈500-670 km) or the lower mantle (>670 km). The great depth of incipient melting implied by this model, and the melt density constraint mentioned above, suggest that komatiitic volcanism may be gravitationally hindered. Although komatiitic magmas are thought to separate from their coexisting crystals at a temperature =200°C greater than that for modern MORBs, their ultimate sources are predicted to be diapirs that, if adiabatically decompressed from initially solid mantle, were more than 700°C hotter than the sources of MORBs and derived from great depth.
We considered the evolution of an initially molten mantle, i.e., a magma ocean. Our model considers the thermal structure of the magma ocean, density constraints on crystal segregation, and approximate phase relationships for a nominally chondritic mantle. Crystallization will begin at the core-mantle boundary. Perovskite buoyancy at > 70 GPa may lead to a compositionally stratified lower mantle with iron-enriched mangesiowiistite content increasing with depth. The upper mantle may be depleted in perovskite components. Olivine neutral buoyancy may lead to the formation of a dunite septum in the upper mantle, partitioning the ocean into upper and lower reservoirs, but this septum must be permeable.
We have examined in detail the analytical method for measuring shear viscosity from the decay of perturbations on a corrugated shock front The relevance of initial conditions, finite shock amplitude, bulk viscosity, and the sensitivity of the measurements to the shock boundary conditions are discussed. The validity of the viscous perturbation approach is examined by numerically solving the second-order Navier-Stokes equations. These numerical experiments indicate that shock instabilities may occur even when the Kontorovich-D’yakov stability criteria are satisfied. The experimental results for water at 15 GPa are discussed, and it is suggested that the large effective viscosity determined by this method may reflect the existence of ice VII on the Rayleigh path of the Hugoniot This interpretation reconciles the experimental results with estimates and measurements obtained by other means, and is consistent with the relationship of the Hugoniot with the phase diagram for water. Sound waves are generated at 4.8 MHz at in the water experiments at 15 GPa. The existence of anelastic absorption modes near this frequency would also lead to large effective viscosity estimates.
Shock compression data to 96 GPa for pure molybdenum, initially heated to 1400°C, are presented. Finite strain analysis of the data gives a bulk modulus at 1400°C, K’S. of 244±2 GPa and its pressure derivative, K’OS of 4. A fit of shock velocity to particle velocity gives the coefficients of US = CO+S UP to be CO = 4.77±0.06 km/s and S = 1.43±0.05. From the zero pressure sound speed, CO, a bulk modulus of 232±6 GPa is calculated that is consistent with extrapolation of ultrasonic elasticity measurements. The temperature derivative of the bulk modulus at zero pressure, θKOSθT|P, is approximately -0.012 GPa/K. A thermodynamic model is used to show that the thermodynamic Grüneisen parameter is proportional to the density and independent of temperature. The Mie-Grüneisen equation of state adequately describes the high temperature behavior of molybdenum under the present range of shock loading conditions.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/3rgr-f070, author = {Polanskey, Carol Ann}, title = {I. Impact Spallation Experiments: Fracture Patterns and Spall Velocities. II. Craters in Carbonate Rocks: An Electron Paramagnetic Resonance Analysis of Shock Damage}, school = {California Institute of Technology}, year = {1989}, doi = {10.7907/3rgr-f070}, url = {https://resolver.caltech.edu/CaltechTHESIS:10172013-085025235}, abstract = {This work is divided into two independent papers.
PAPER 1.
Spall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4 g lead bullet to a 0.04 g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small scale experiments are considered in detail.
The targets were also bisected to observe the pattern of internal fractures. A series of fractures were observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical “near surface zone” predicted by the spallation model. Thus, between this boundary and the free surface, the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
PAPER 2.
Carbonate samples from the nuclear explosion crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance, EPR. The first series of samples for OAK Crater were obtained from six boreholes within the crater, and the second series were ejecta samples recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen limestone, which had been shocked to known pressures.
The results of the OAK borehole analysis have identified a thin zone of highly shocked carbonate material underneath the crater floor. This zone has a maximum depth of approximately 200 ft below sea floor at the ground zero borehole and decreases in depth towards the crater rim. A layer of highly shocked material is also found on the surface in the vicinity of the reference bolehole, located outside the crater. This material could represent a fallout layer. The ejecta samples have experienced a range of shock pressures.
It was also demonstrated that the EPR technique is feasible for the study of terrestrial impact craters formed in carbonate bedrock. The results for the Meteor Crater analysis suggest a slight degree of shock damage present in the β member of the Kaibab Formation exposed in the crater walls.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/7TQ9-X746, author = {Vidale, John Emilio}, title = {Application of Two-Dimensional Finite-Difference Wave Simulation to Earthquakes, Earth Structure, and Seismic Hazard}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/7TQ9-X746}, url = {https://resolver.caltech.edu/CaltechTHESIS:10132011-090721112}, abstract = {Although the earth is 3-dimensional (3-D), numerical simulations of wave propagation through laterally heterogeneous media are easier to formulate and more practical to use in 2-D. In this thesis, schemes to model seismic wave propagation through laterally varying structures with 2-D numerical algorithms are developed and applied to earthquake and explosion problems.
In Chapter 1, 2-D source expressions that have the same radiation patterns as their 3-D counterparts are derived which can rectify the following three problems: the use of 2-D simulations generally results in “line source tails” on what would be impulsive arrivals in 3-D, 1/√R rather than 1/R amplitude decay for body waves, and no decay rather than 1/√R amplitude decay for surface waves. Because this technique approximately transforms waves from a cartesian 2-D grid to a cylindrically symmetric 3-D world, slightly anisotropic geometrical spreading in 2-D better approximates isotropic spreading in 3-D than simple isotropic spreading in 2-D does. In Section 1.7, a correction to the explosive source expression reduces energy traveling vertically out of the source region, but leaves unchanged the energy traveling laterally out of the source region. In some cases, this correction will significantly improve the results of using a 2-D grid to simulate elastic wave propagation from an explosive point source.
In Chapter 2, synthetic seismograms are constructed for the strong motions of the 1968 Borrego Mountain earthquake recorded at EI Centro. A good fit to the data results from using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling. Shallow faulting is no longer necessary to explain the long-period surface-wave development.
Synthetic seismograms calculated for the 1971 San Fernando earthquake show strong effects due to lateral variation in sediment thickness in the San Fernando valley and the Los Angeles basin. Using previously determined basin structure and teleseismically determined source parameters, two-dimensional SH and P-SV finite difference calculations can reproduce the amplitude and duration of the strong motion velocities recorded across the basins in Los Angeles in the period range from 1 to 10 seconds. The edges of basins nearest the seismic source show ground motion amplification up to a factor of three, and tend to convert direct shear waves into Love and Rayleigh waves that travel within the basins. The computed motions are sensitive to the mechanism and location of earthquakes. A strike-slip earthquake on the Newport-Inglewood fault zone, for example, would produce different patterns of peak velocity and duration of shaking across the San Fernando and Los Angeles basins.
In Chapter 3, the effect of shallow station structure and lateral velocity variation are investigated for records of the Amchitka explosion Milrow. The differences between the Meuller-Murphy, Heimberger-Hadley, and von Seggern-Blandford reduced displacement potential (RDP) source representations are small compared to the differences between using various possible velocity structures.
Creager and Jordan (1986) propose that penetration of subducting slabs under the Kurile Islands and other subduction zones to depths of at least 1000 km is necessary to explain the t ravel time anomalies of deep earthquakes. Such penetration would also affect the amplitudes and waveforms of the body waves from these earthquakes. In Chapter 4, synthetic seismograms appropriate for a record section in a plane perpendicular to the strike of the slab are presented using a coupled finite-difference and Kirchhoff method. An inferred shear-wave version of the compressional-wave velocity structure of Creager and Jordan (1986) produces an amplitude decrease up to a factor of four and waveform broadening up to 20 seconds for SH arrivals with a take-off angle pointing straight down t he slab. Slabs that extend only 300 km below the earthquake but are half as thick and twice as anomalously fast as Creager and Jordan ’s (1986) velocity model will roughly preserve the travel time variation pattern, and show less waveform broadening, but produce first arrivals that are emergent. Slabs that become thicker with depth show less waveform broadening. Reconciliation of the amplitude, waveform distort ion, and timing of body waves from deep events is necessary to understand the geometry of slabs near and below the 6.50 km discontinuity.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Hager, Bradford}, } @phdthesis{10.7907/mvdj-ty73, author = {Scott, David Russell}, title = {Magmons: Solitary Waves Arising in the Buoyant Ascent of Magma by Porous Flow through a Viscously Deformable Matrix}, school = {California Institute of Technology}, year = {1987}, doi = {10.7907/mvdj-ty73}, url = {https://resolver.caltech.edu/CaltechTHESIS:04052019-172938000}, abstract = {The dynamics of partially molten regions of the Earth’s mantle are studied using a combination of theoretical, experimental, and numerical techniques. The physical model is based on experimental observations of partially molten ultramafic rocks and incorporates two elements: buoyancy-driven porous flow of magma through a viscously deformable matrix, and buoyancy-driven circulation of the whole rock.
The first element of this model is analogous to buoyancy-driven pipe flow of a liquid through a denser and more viscous wall fluid. Laboratory experiments on this system illustrate the phenomenon of solitary waves. These are waves of larger pipe radius that ascend a uniform pipe of smaller radius. The waves are very nearly conserved in collisions. These, and the corresponding waves of higher porosity that arise in one-dimensional porous flow, are characterized further by analysis and numerical experiments.
The full system, incorporating circulation in a multidimensional porous medium, also displays solitary waves governed by the same basic processes as the one-dimensional waves. Analysis and numerical experiments show that the multidimensional waves have a circular or spherical form.
A possible natural manifestation of this fluid dynamical phenomenon is in igneous processes. Magmons, as the waves are called in that setting, probably have wavelengths of kilometers and velocities of centimeters per year. Magma ascent in magmons may account for episodicity in igneous emplacement. Also, a magmon can collect and mobilize a small degree of partial melt without disturbing its geochemical signature. In a partially molten region the characteristic wavelength of magmons will always be superimposed on that of large scale variations in porosity.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/ncf0-0c06, author = {Richards, Mark Alan}, title = {Dynamical Models for the Earth’s Geoid}, school = {California Institute of Technology}, year = {1986}, doi = {10.7907/ncf0-0c06}, url = {https://resolver.caltech.edu/CaltechTHESIS:02122016-151411807}, abstract = {The Earth’s largest geoid anomalies occur at the lowest spherical harmonic degrees, or longest wavelengths, and are primarily the result of mantle convection. Thermal density contrasts due to convection are partially compensated by boundary deformations due to viscous flow whose effects must be included in order to obtain a dynamically consistent model for the geoid. These deformations occur rapidly with respect to the timescale for convection, and we have analytically calculated geoid response kernels for steady-state, viscous, incompressible, self-gravitating, layered Earth models which include the deformation of boundaries due to internal loads. Both the sign and magnitude of geoid anomalies depend strongly upon the viscosity structure of the mantle as well as the possible presence of chemical layering.
Correlations of various global geophysical data sets with the observed geoid can be used to construct theoretical geoid models which constrain the dynamics of mantle convection. Surface features such as topography and plate velocities are not obviously related to the low-degree geoid, with the exception of subduction zones which are characterized by geoid highs (degrees 4-9). Recent models for seismic heterogeneity in the mantle provide additional constraints, and much of the low-degree (2-3) geoid can be attributed to seismically inferred density anomalies in the lower mantle. The Earth’s largest geoid highs are underlain by low density material in the lower mantle, thus requiring compensating deformations of the Earth’s surface. A dynamical model for whole mantle convection with a low viscosity upper mantle can explain these observations and successfully predicts more than 80% of the observed geoid variance.
Temperature variations associated with density anomalies in the man tie cause lateral viscosity variations whose effects are not included in the analytical models. However, perturbation theory and numerical tests show that broad-scale lateral viscosity variations are much less important than radial variations; in this respect, geoid models, which depend upon steady-state surface deformations, may provide more reliable constraints on mantle structure than inferences from transient phenomena such as postglacial rebound. Stronger, smaller-scale viscosity variations associated with mantle plumes and subducting slabs may be more important. On the basis of numerical modelling of low viscosity plumes, we conclude that the global association of geoid highs (after slab effects are removed) with hotspots and, perhaps, mantle plumes, is the result of hot, upwelling material in the lower mantle; this conclusion does not depend strongly upon plume rheology. The global distribution of hotspots and the dominant, low-degree geoid highs may correspond to a dominant mode of convection stabilized by the ancient Pangean continental assemblage.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Hager, Bradford}, } @phdthesis{10.7907/14q2-fa62, author = {Le Bras, Ronan}, title = {Methods of Multiparameter Inversion of Seismic Data Using the Acoustic and Elastic Born Approximations}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/14q2-fa62}, url = {https://resolver.caltech.edu/CaltechTHESIS:10092013-140441093}, abstract = {This thesis presents two different forms of the Born approximations for acoustic and elastic wavefields and discusses their application to the inversion of seismic data. The Born approximation is valid for small amplitude heterogeneities superimposed over a slowly varying background. The first method is related to frequency-wavenumber migration methods. It is shown to properly recover two independent acoustic parameters within the bandpass of the source time function of the experiment for contrasts of about 5 percent from data generated using an exact theory for flat interfaces. The independent determination of two parameters is shown to depend on the angle coverage of the medium. For surface data, the impedance profile is well recovered.
The second method explored is mathematically similar to iterative tomographic methods recently introduced in the geophysical literature. Its basis is an integral relation between the scattered wavefield and the medium parameters obtained after applying a far-field approximation to the first-order Born approximation. The Davidon-Fletcher-Powell algorithm is used since it converges faster than the steepest descent method. It consists essentially of successive backprojections of the recorded wavefield, with angular and propagation weighing coefficients for density and bulk modulus. After each backprojection, the forward problem is computed and the residual evaluated. Each backprojection is similar to a before-stack Kirchhoff migration and is therefore readily applicable to seismic data. Several examples of reconstruction for simple point scatterer models are performed. Recovery of the amplitudes of the anomalies are improved with successive iterations. Iterations also improve the sharpness of the images.
The elastic Born approximation, with the addition of a far-field approximation is shown to correspond physically to a sum of WKBJ-asymptotic scattered rays. Four types of scattered rays enter in the sum, corresponding to P-P, P-S, S-P and S-S pairs of incident-scattered rays. Incident rays propagate in the background medium, interacting only once with the scatterers. Scattered rays propagate as if in the background medium, with no interaction with the scatterers. An example of P-wave impedance inversion is performed on a VSP data set consisting of three offsets recorded in two wells.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/j2xf-gq29, author = {Humphreys, Eugene Drake}, title = {Studies of the Crust-Mantle System Beneath Southern California}, school = {California Institute of Technology}, year = {1985}, doi = {10.7907/j2xf-gq29}, url = {https://resolver.caltech.edu/CaltechTHESIS:02142013-085850235}, abstract = {A back-projection method of tomographic reconstruction is adapted to inverted seismic travel-time data. The problems encountered in inverting these data include ray set inhomogeneity and anisotropy and the three-dimensionality of the space interrogated. Jacobi iteration, deconvolution and variable ray weighting are shown to work well in augmenting the basic back-projection method to produce a well-focused image. Applications of the various focusing algorithms are shown to have a degree of success that depends on the ray geometry used. Also, the ability to reconstruct an accurate image when the data include moderate amounts of noise is shown to be good.
P-wave teleseismic travel time delays recorded by the southern California array are inverted with the tomographic method to obtain variations in the P-wave velocity structure to a depth of 750 km. Two major anomalies are imaged. A curtain-like E-W trending high velocity feature is found directly beneath the Transverse Ranges. This feature is about 50 km in thickness, extends in depth to a maximum of about 250 km on its eastern end, and attains a maximum velocity that is about 3% greater than average mantle at the same depth beneath southern California. A zone of low-velocity material is found in the uppermost 100 km beneath the region of the Salton Trough. The seismic velocities here are depressed by about 4%.
These anomalous regions are interpreted to be related to the geologic processes that have been active recently in southern California. Scaling relations are used to estimate that the Transverse Range anomaly is about 500°C colder and 1% more dense than average southern California mantle of the same depth, while the Salton Trough anomaly is about 1/2% less dense and contains about 3% melt. The density distribution drives a flow of upper mantle material from the Salton Trough region towards the Transverse Ranges, where it sinks into the mantle to form the feature seen beneath these ranges. Mantle flow results in tractions that act on the base of the lithosphere to produce stresses within the lithosphere that are tensile in the Salton Trough and compressive in the Transverse Ranges. These stresses are thought to account for the physiography seen in these provences.
The southern California crust is modeled using late Quaternary slip rates on major faults, and a kinematic description is determined that has: 1) only local sites of convergence in the Transverse Ranges, and 2) the occurrance of significant strain rates near to the southern California coast, including the western Transverse Ranges.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/C9GZ-3121, author = {Boslough, Mark Bruce}, title = {Shock-Wave Properties and High-Pressure Equations of State of Geophysically Important Materials}, school = {California Institute of Technology}, year = {1984}, doi = {10.7907/C9GZ-3121}, url = {https://resolver.caltech.edu/CaltechETD:etd-09262002-154053}, abstract = {Shock wave (Hugoniot), shock temperature, and release data are presented for several geophysically important, refractory materials. A sensitive multichannel optical pyrometer was developed to measure shock temperatures (2500 to 5600°K at pressures from 48 to 117 GPa) in anorthite (CaAl2Si2O8) glass. Shock temperatures of 3750 to 6000°K at pressures from 140 to 182 GPa were measured in calcium oxide (CaO). Temperature data were used to constrain the energetics of the B1-B2 phase transition at 70 GPa in CaO, and to construct a finite-strain equation of state for CaO consistent with previous Hugoniot data.
The new CaO equation of state was used with equation of state parameters of other oxides to construct a theoretical mixed oxide Hugoniot of anorthite, which is in agreement with new Hugoniot data above about 50 GPa, determined using new experimental techniques developed in this study. The mixed oxide model, however, overestimates the shock temperatures, and does not accurately predict measured release paths. Both shock temperature and release data for anorthite indicate that several high pressure phase regions of stability exist above 50 GPa. A similar mixed oxide Hugoniot was constructed for lunar gabbroic anorthosite, and agrees with two new Hugoniot points at 120 GPa. Release data from lunar gabbroic anorthosite shocked to 120 GPa give evidence for shock vaporization.
Because the densities and bulk properties of CaO and the high pressure phase or phases of anorthite are so close to those determined seismologically for the lower mantle, the amount of these materials present in the lower mantle is not well constrained. The possibility of significant enrichment of the lower mantle in these refractory materials, as predicted by inhomogeneous accretion models, is still open.
A simple model is developed to explain the measured time dependences of radiated light in the shock temperature experiments, and constrain the absorption coefficient of the shocked material. The absorption coefficient is found to be an increasing function of shock pressure in shocked anorthite glass.
Hugoniot and release paths were determined using electromagnetic particle velocity gauges for San Gabriel anorthosite and San Marcos Gabbro shocked to peak stresses between 5 and 11 GPa. The data indicate a loss of shear strength in both rocks, and a partial phase transition of the anorthosite to a denser phase. This implies that estimates of shock wave attenuation in these materials based on elastic-plastic models are too high, and previously calculated amounts of internal energy gained by surface materials from impact or explosion events have been underestimated.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/GNES-QH83, author = {Gillespie, Alan Reed}, title = {Quaternary Glaciation and Tectonism in the Southeastern Sierra Nevada, Inyo County, California}, school = {California Institute of Technology}, year = {1982}, doi = {10.7907/GNES-QH83}, url = {https://resolver.caltech.edu/CaltechETD:etd-04102003-122837}, abstract = {The southeastern Sierra Nevada consists of three geographic regions. From west to east, they are: an upland region across the crest, a steep east-facing escarpment along which Owens Valley has partly subsided, and foothill blocks intermediate to the Sierra Nevada and Owens Valley. Farther east, Owens Valley is a deep graben separating the Sierra Nevada and the Inyo Range.
The main goals of this thesis were the detailed mapping of Quaternary glacial and other deposits in these regions, dating of critical events, and geomorphic analysis of the range front. The focus was on Pleistocene moraines near the range front. The motivation of this research was to improve our understanding of the chronology of Pleistocene events, to characterize details of the tectonic history of the Sierra, to infer faulting, erosion, and deposition rates, and to provide a basis for the comparison of the Quaternary geology in the southeastern Sierra and in more intensively studied regions in the central and northern Sierra and elsewhere.
The study area extended from the alluvial fans of Owens Valley west to the Sierra crest from latitude 36°45’ N to 37°00’ N. It included the southern part of the Big Pine volcanic field, an eruptive center for basaltic lavas for most of the Pleistocene Epoch. Elevations within the study area ranged from about 1000 m (Owens Valley) to about 4000 m (peaks along the crest).
Throughout the study area the principal rocks are granodiorite and quartz monzonite of Cretaceous age. Plutons are rather small, and individual drainages generally include more than one. In the southern part of the study area, Jurassic-Triassic metavolcanic rocks are found as roof pendants. These rocks, originally ranging in composition from basalt to rhyolite, are most common near the Sierra crest. In the northern canyons of the study area, Paleozoic metasedimentary rocks including sandy marbles and biotite schist replace the metavolcanic pendants. The foothill blocks are identical to the Sierras in composition.
Below the foothills coalescing alluvial fans grade a few km east to the alluvium and lacustrine sediments of the Owens River and Owens Lake. These sediments have been shown in geophysical studies to mask a second escarpment as high as the one of the range front, and the total bedrock relief from the Sierra crest to the floor of the graben is as much as 6 km.
During the Quaternary Period the southeastern Sierra Nevada was characterized by the down-faulting of Owens Valley along two zones, one a series of normal faults along the range front (Independence Fault) and the other a series of faults along the center of the valley (Owens Valley fault zone). This same period has seen the cutting of deep canyons through the 2-km-high escarpment. During repeated glaciations these canyons were widened and deepened. Traces of at least seven glaciations were found during this study. Moraines and other deposits left during these glaciations could be distinguished based on the degree of weathering of granitic clasts, vegetative cover, and morphologic characteristics. Absolute age limits were obtained for two of the Pleistocene glaciations by radiometric dating of basalt flows interfingered with the moraines.
Three of the recognized glaciations, probably corresponding to the Matthes, Recess Peak, and Hilgard neoglaciations found by J.H. Birman in the central Sierra Nevada, occurred during the Holocene Epoch. The youngest glaciers (Matthes glaciation) left unconsolidated and unvegetated till in stagnant rock glaciers and moraines in cirques on high peaks. Some rock glaciers are still ice-cored. Extending out from the cirques and into the upper reaches of the canyons are moraines correlating to the Recess Peak glaciation. Till is generally consolidated and supports heavy lichen growth and bushes but few trees. The oldest Holocene glaciation (Hilgard) left few large moraines in the study area. Hilgard glaciers extended much farther down-canyon than the younger Holocene glaciers, sometimes within one or two km of the Tioga terminal moraines. Those Hilgard terminal moraines which were found have been barely breached by streams. Moraines tend to be heavily forested, and lakes are largely unsedimented. The Hilgard glaciation may have simply been the last stade of the Tioga glaciation from the evidence found in this study.
At least four Pleistocene glaciations occurred in the southeastern Sierra Nevada. All four postdate most of the significant incision of streams through the escarpment. The three youngest probably correlate with the Tioga, Tenaya, and Tahoe stages (in order of increasing age) recognized throughout the Sierra. In each case, moraine morphology has been well preserved. Tioga moraines were found down to about 2200 m elevation. Nested sets of moraines were common. The terminal moraines of the youngest of these were sometimes intact. lakes were rare; one (Sawmill Meadow) was completely sedimented. Granitic boulders in the moraines were largely unweathered. Weathering of boulders in Tenaya moraines was similar, but a small fraction of granitic boulders were grusy. Boulders from Tahoe moraines were conspicuously weathered, and the moraines themselves were rounded and gullied.
The oldest group of moraines probably significantly predates the Tahoe glaciation. It is nevertheless post-Sherwin. Moraines in this group were found in five of the eight canyons studied. While obviously eroded, these moraines still retained their original shape. All surficial boulders were heavily weathered, but some exposed in road cuts were fresh. No moraines of Sherwin age were identified, although Sherwin till is widespread only a few km to the north. However, on plateaus and ridges 200 to 300 m above the modern canyons near the Sierra crest were found ancient diamictons, some of which could be till. Remnants of U-shaped valleys preserved as high passes across the crest or as cols between canyons east of the crest may be testimonials to ancient glaciers of Sherwin age or older.
Radiometric dating (40Ar - 39Ar) of basalts interfingered with moraines in Sawmill Canyon provided a new upper limit of 0.12 my for a moraine of the Tahoe glaciation, and a range of 0.13 - 0.46 my for one pre-Tahoe glaciation. These results confirm that the Tahoe glaciation occurred during the Wisconsin stage of the continental ice age, and conclusively demonstrate the existence of pre-Wisconsin glaciers in the southern Sierra. Relative dating based on acoustic wave speeds through weathered boulders on the moraines indicates the age of the pre-Wisconsin moraine may be close to the upper limit.
Alluvial fans appear to have aggraded early in the Wisconsin glaciation (Tahoe glaciation). Subsequently, the fan heads have been incised and the locus of deposition has moved eastward down the fans. The Tenaya and Tioga glaciers during the late Wisconsin stage left outwash plains and terraces along streams cut into the older fans, but aggradation during these events was considerably less than earlier.
Three ages of fans were found. The oldest fanglomerate probably is pre-Wisconsin and is exposed in regions protected from later deposition. The heavily weathered fan deposits of this group overlie basalts which appear to be contemporaneous with dated 1.1 - 1.2 my-old basalts nearby. In the middle elevations of the fans, roughly 10 m of fanglomerate was deposited over the old fanglomerate, probably during the Tahoe glaciation. Deposition rates probably are about 0.1 mm/y for the late Pleistocene Epoch. The extent and distribution of the youngest fans (Tenaya-Tioga) are variable, but they are generally found downstream from the incised Tahoe fan heads.
Faulting along the range front appears to have been dip-slip only. The offset rate along the range-front faults was determined at several canyons where the fault crossed dated moraines or lava flows. At least during the Wisconsin glaciation faulting on this zone appears to have been erratic, with rates ranging from zero to 0.5 mm/y or more. Offset moraines and terraces at Independence Creek indicated a faulting rate of 0.1 mm/y. Only a few km to the north, Tahoe moraines of both forks of Oak Creek were not offset at all, although scarps could be seen on adjacent hillsides. At Sawmill Creek an offset lava flow gave a lower limit of 0.5 mm/y. It seems that during the late Pleistocene Epoch, offset on the range front faults has been less than on the mid-valley faults east of the study area. Geodetic studies have suggested modern strain rates of 2.2 mm/y for the Owens Valley fault zone.
Basalts found in canyons through the escarpment and on terraces and ridges in the foothills to the east document stream erosion during the Pleistocene Epoch. Ridgetop basalts, dated at 1.2 my, stand at least 125 m above the modern streams through the foothills. This indicates an erosion rate of ~ 0.1 mm/y. A comparable rate of ~ 0.15 mm/y for the last 0.46 my was found for Sawmill Creek within the Sierra Nevada. Thus at least during the late Pleistocene Epoch erosion rates in the Sierra and in the foothills have been similar.
Patches of boulders and gravels atop the basalt show that some time after 1.2 my BP the foothill block was submerged by alluvial fans. Incision may have begun in response to the inception or renewal of subsidence of the graben along the Owens Valley fault zone.
Extensive volcanism in the Big Pine Volcanic field appears to have begun at least 1.2 my ago, and has continued sporadically up to perhaps 0.05 my ago. Minor eruptions may have occurred more recently.
The eastern escarpment of the Sierra Nevada consists of two zones of truncated ridges. Within the study area, the upper zone is about 950 m high; the lower is about 750 m high. Triangular facets of the upper zone have a gradient of only ~ 24°, lower than slopes of ~ 29° in the lower zone. This could be explained if subsidence of Owens Valley along the range-front faults occurred in two great pulses.
Both absolute and relative dating methods were refined for this study. Absolute dating of the K-poor basaltic lavas was done indirectly, by 40Ar - 39Ar analysis of K-rich granitic xenoliths found in the lava. These ancient xenoliths were partially degassed of their accumulated 40Ar during heating in the magma, and it proved possible to date this heating event.
In addition to conventional relative dating methods, a new quantitative approach based on the speed of acoustic waves through individual clasts in a deposit was investigated. This method had been used only once before, on terrace deposits. The technique proved to be very useful, and was capable of discriminating moraines successfully in well-studied canyons in the central Sierra. Acoustic wave speeds may be controlled by the abundance of intergranular cracks in granitic boulders. If this is the case, then this technique relies on different processes than those exploited by conventional methods of relative dating. The successful application to moraines in this study enhances our ability to analyse glacial sequences and complements conventional semi-quantitative methods of relative dating.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/bwpb-4c04, author = {Cipar, John Joseph}, title = {Seismic Source Processes and Tectonics: Observations of Four Intracontinental Earthquakes}, school = {California Institute of Technology}, year = {1981}, doi = {10.7907/bwpb-4c04}, url = {https://resolver.caltech.edu/CaltechETD:etd-09152006-102853}, abstract = {This thesis presents studies of the source processes of four shallow earthquakes and their relation to regional tectonics. In the first chapter, long-period teleseismic P and S waves from the Haicheng, China earthquake of February 4, 1975 are compared directly to time domain synthetic seismograms to infer source parameters. The P-wave focal mechanism indicates that faulting was dominantly left-lateral strike-slip along a northwest striking nodal plane (strike = 288°, dip = 78°N, rake = 342°). The strike of this nodal plane agrees with the trend of the aftershock distribution. Azimuthal variation of P-wave duration is attributed to fault rupture 22 km in a northwesterly direction, along strike of the aftershock zone. There is considerable discrepancy between the observed SH waves and synthetics computed using this model. These discrepancies are due to either structural complexities in the source region or change in fault mechanism as the rupture propagated along strike. Seismic moment, average dislocation and stress drop are computed to be 2.7 x 1026 dyne-cm, 2.5 meters and 48 bars, respectively.
The remaining three chapters present a detailed examination of seismograms recorded by the 1976 Friuli, Italy earthquake (May 6, 1976, MS = 6.5) and two major aftershocks (both on September 15, 1976 at 03h 15m, MS = 6.0 and 09h 21m, MS = 5.9). Teleseismic long-period body waves and surface waves radiated by the mainshock and 09h 21m aftershock are studied in Chapter Two to determine source characteristics. Focal mechanisms along with geological evidence suggest that both events represent underthrusting of the Friuli Plain beneath the Southern Alps. The depths of both earthquakes, estimated by matching synthetic body wave seismograms to observations, are found to lie between 6 and 10 km. Synthetic seismogram calculations which include source directivity effects suggest that the fault length of the mainshock is approximately 16 to 24 km assuming a rupture velocity of 3.0 km/sec. Observations of 100 sec Rayleigh waves confirm the body wave focal mechanism, but suggest that the seismic moment of the mainshock is 5 x 1025 dyne-cm compared to 2.9 x 1025 dyne-cm estimated from body waves. The P-wave moment of the aftershock is 1 x 1025 dyne-cm.
In Chapter Three, short-period records are modeled to obtain additional details of the source time history. Two point sources of radiation are required to adequately model the aftershock short-period records. For the 09h 21m aftershock, the model derived from short-period records also produces good fits to the long-period data. The SP model for the 03h 15m aftershock, on the other hand, predicts long-period synthetics which do not agree with the observations. In particular, the SP moment (0.37 x 1025 dyne-cm) is about 2-1/2 times smaller than the LP moment (1 x 1025 dyne-cm). Adding a long-period component to the SP model considerably improves LP waveform and moment agreement. In the case of the mainshock, a reasonable fit to the observed SP data is obtained using three point sources of radiation. However, LP synthetics computed using this model do not agree with the observations, and the SP moment (0.65 x 1025 dyne-cm) is a small fraction of the LP moment (3-5 x 1025 dyne-cm). Time function durations indicate that the individual events inferred from the SP records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars. In comparison, overall stress drops estimated from LP data are found to be 12 bars (mainshock) and 24 bars (09h 21m aftershock). Strong-motion accelerograms are used to put additional constraint on the source geometry of the 09h 21m aftershock.
The 03h 15m and 09h 21m aftershocks are the culminating events of a series of large aftershocks which began on September 11, 1976. Cumulative seismic moment of the Friuli aftershock sequence was as large as the moment released by the mainshock. By comparison, aftershock moments of California earthquakes are typically 1 to 10 percent of the mainshock moment. The large size, location and focal mechanism of the aftershocks suggest that they represent failure of major stress concentrations remaining after the mainshock.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/VSBK-ZA43, author = {Lyzenga, Gregory Allen}, title = {Shock temperatures of materials : experiments and applications to the high pressure equation of state}, school = {California Institute of Technology}, year = {1980}, doi = {10.7907/VSBK-ZA43}, url = {https://resolver.caltech.edu/CaltechETD:etd-08032004-150047}, abstract = {The experimental determination of temperatures in the high-pressure shocked state of condensed matter provides a useful supplement to equation-of-state models derived from Hugoniot measurements. An optical pyrometry technique has been developed to obtain temperature measurements during impact-driven shock wave experiments with solid and liquid samples at pressures near 100 GPa. Experimental results confirm that throughout moderate ranges of shock pressure amplitude, transparent dielectrics emit thermal radiation from the region of the shock front, with a spectrum which is characteristic of the Hugoniot state temperature. Shock temperatures in sodium chloride crystals have been measured in the pressure range 70-105 GPa. The observed temperatures, between 4000 and 8000 K, are in agreement with the results of earlier determinations and with calculations assuming the occurrence of shock-induced melting. Results of experiments to measure shock temperatures in metallic silver include a successful measurement of 5950 K at a pressure of 185 GPa. This result is consistent with the melting of silver under shock, with a melting pressure dependence described by the Lindemann criterion.
Shock temperature measurements in silica (SiO2) have produced anomalous results suggestive of melting occurring in the stishovite phase near 100 GPa pressure and 4700 K temperature. Experimental measurements with [alpha]-quartz and fused silica samples extend from pressures of approximately 60 GPa to 140 GPa, with shock temperatures between approximately 4500 K and 7000 K. The experimental data allow quantification of the thermodynamic relations among silica phases, including heats of transition and the Gruneisen parameter. Shock temperatures in single crystal forsterite (Mg2SiO4) between pressures of 150 GPa and 175 GPa range from 4500 K to 4950 K, a result which is consistent with occurrence of a polymorphic solid state transition accompanied by a substantial heat of transition (~1.5 MJ/kg). These results have potentially important implications for solid earth geophysics, and knowledge of the melting curves of candidate minerals of the earth’s mantle provides some constraints on the geotherm.
Hugoniot temperatures have been measured in liquid water between approximately 50 GPa and 80 GPa, with results ranging from 3500 K to 5400 K. The observed temperatures are well reproduced by theoretical calculations assuming a constant specific heat model, but further work is required to characterize fully the thermal variation of H2O properties at high temperature. Compression measurements in pressure-volume states other than Hugoniot shock states and, in particular, in states of compression at constant entropy can provide both independent thermal equation-of-state information and the properties of high-density condensed phases inaccessible to shock wave experiments. Numerical calculations have been carried out for hypothetical experiments on water as well as carbon dioxide and liquid molecular hydrogen. The results of these calculations indicate that various experimental impact configurations may be employed to convert shock compression into isentropic compression, with pressures on the order of 100 GPa attained via impact velocities of a few kilometers per second. In the case of water, a net entropy production of a few percent of the Hugoniot entropy at the same pressure is predicted on the basis of these calculations.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/9BJQ-N519, author = {Gibbons, Rex Vincent}, title = {Experimental effects of high shock pressure on materials of geological and geophysical interest}, school = {California Institute of Technology}, year = {1974}, doi = {10.7907/9BJQ-N519}, url = {https://resolver.caltech.edu/CaltechETD:etd-11032005-141608}, abstract = {Shock recovery studies have been performed on a number of materials of geological and geophysical significance using a shock-loading propellant gun. These materials, including silicate glasses, feldspar, orthopyroxene, and pyroxenoid, have been shock-loaded to pressures up to approximately 550 kilobars. Optical and electron microscopic, optical spectral, and x-ray diffraction studies have been carried out on the recovered samples to determine the permanent effects of the shock-loading and the applicability of such information to research on naturally shocked lunar and terrestrial rocks and meteorites. The data on the pyroxene and feldspar are discussed in terms of their usefulness in interpreting, understanding, and calibrating the pressure and temperature conditions of shock metamorphism. The most significant observations include (1) the behavior of the silicate glasses, especially the occurrence of permanent densification until high postshock temperatures cause reversion to low density glass, (2) the permanent reduction of Mn(III) to Mn(II) by shock-loading to 496 kilobars, (3) the shock vitrification of calcic plagioclase to diaplectic and shock-fused glasses at pressures above 300 kilobars, (4) the shockproduction of deformation lamellae in bronzite, and (5) the formation of shock glass in bronzite at 226 kilobars.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/zzpq-2876, author = {Lagus, Peter Leonard}, title = {The Equations of State of Hydrogen and Argon; Applications to the Jovian Interior}, school = {California Institute of Technology}, year = {1974}, doi = {10.7907/zzpq-2876}, url = {https://resolver.caltech.edu/CaltechTHESIS:12072020-234014838}, abstract = {Hugoniot data for solid argon (initially at 77°K and l bar) and solid hydrogen (initially at 5°K and 1 bar) have been obtained to 143 kbar and 6.4 kbar respectively utilizing a propellant gun. The argon data (at volumes of 15.28, 14.84 and 14.64 cc/mole) are in fair agreement with previous shock data, and in excellent agreement with recent theoretically predicted Hugoniots. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cc/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the present data are consistent with the assumption that γ/V is constant. Furthermore, to compressions of V/V₀ ≃ 0.65, no gross inconsistencies exist between shock-wave and isothermal compression measurements in solid hydrogen.
A simple equation of state (E0S) for molecular hydrogen based on a spherically averaged De Boer-type repulsion potential which explicitly includes the zero point energy reproduces experimental pressure-volume data between 5 kbar and 370 kbar. This molecular equation of state when combined with recent metallic equations of state implies a molecular to metallic phase transition pressure of 1.9 ± 0.4 Mbar at 0°K.
A thermally expanded model of Jupiter which incorporates this molecular equation of state, recent metallic hydrogen and helium equations of state, and a van der Waals-type atmosphere yields a model with a hydrogen abundance of x = 0.57. However, the interior temperatures are everywhere above the melting temperature of metallic hydrogen.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, } @phdthesis{10.7907/SK7X-EE20, author = {Davies, Geoffrey Frederick}, title = {Elasticity of Solids at High Pressures and Temperatures : Theory, Measurement, and Geophysical Application}, school = {California Institute of Technology}, year = {1973}, doi = {10.7907/SK7X-EE20}, url = {https://resolver.caltech.edu/CaltechTHESIS:02072018-154915291}, abstract = {A theory for describing the elasticity of solids at simultaneous high pressures and high temperatures is developed by incorporating the fourth-order ahnarmonic theory of lattice dynamics into finite strain theory. The theory is applied to the analysis of a variety of data for MgO, SiO2 and NaCl, and the results for MgO and SiO2 used as the basis of a discussion of the constitution of the lower mantle. New results are reported of measurements of elastic properties of MgO shock-compressed to over 500 Kb.
The condition that finite strain equations be frame- indifferent is shown to require that only strain tensors belonging to a class of frame-indifferent strain tensors be used in finite strain expansion. It is shown that the generality of finite strain theory is not impaired by the inclusion of an explicit theory of thermal effects. Explicit equations for isotherms, isentropes and Hugoniots and for the effective elastic moduli of materials of cubic symmetry under hydrostatic stress are derived. The primary parameters of these equations are related to the elastic moduli and their pressure and temperature derivatives in an arbitrary reference state using thermodynamic identities, some of which are derived here.
Hugoniot data corresponding to different initial sample densities of MgO, SiO2 and NaCl and original ultrasonic data of NaCl are used to test both the compressional and thermal parts of the theory, and to refine the equations of state of these materials. The frame-indifferent analogue, E, of the usual “Eulerian” strain tensor, ε, is found to usually give faster convergence of finite strain expansions than the “Lagrangian” strain tensor, η. The effect of usinq different strain measures on the values of parameters derived from data is demonstrated, and the adverse effects of using inappropriately derived parameters in extrapolation equations is demonstrated. Thermal effects in Hugoniot data are reasonably well described, but higher-order anharmonic effects appear to be required in the theory in order to describe the high temperature ultrasonic and thermal expansion data.
Measured velocities of rarefaction waves propagating into shocked MgO are in accord with a two-stage longitudinal (elastic)-hydrodynamic (plastic) decompression model, and constrain the high-pressure elastic moduli of MgO.
The effects on the determination of the lower mantle constitution of temperature, varying composition, the presence of phases denser than oxides mixtures, and the presence of iron in the “low-spin” electronic state are estimated, and a trade-off between many of these factors demonstrated. Iron content could range between 6% and 15% by weight of FeO. Silica content could range from 33% to 50% or more by weight. Phases a few percent denser than oxides mixtures seem to be likely. The temperature is very indeterminable.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J.}, }