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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenMon, 27 Nov 2023 19:03:43 +0000Periodic Variations of the Gravitational Force. A Gravity Survey in the Monk Hill Area. Transmission of Shot Impulses in Shallow Water
https://resolver.caltech.edu/CaltechTHESIS:08172010-101104666
Authors: Geldart, Lloyd Philip
Year: 1949
DOI: 10.7907/YH1P-CT82
<p>Part I:
Using a La Coste and Romberg gravimeter, readings were taken every half hour for 72 hours immediately preceding full moon in the sub-basement of Mudd Building, California Institute of Technology, and for 56 hours immediately following in the interferometer building on Mount Wilson. Observed values were compared with values calculated on the hypothesis of a rigid earth, the results showing more yielding at Mount Wilson (22%) than at Mudd Building (16%). Effects due to ocean tides and barometric changes were estimated. After the removal of drift and earth tide effects, the residuals showed periods of 24, 12, 6, and 2 hours, the 24 hour period being very strong at Mount Wilson.</p>
<p>Part II:
Using a La Coste and Rombert gravimeter, gravity values were obtained at 65 stations in the vicinity of Monk Hill, Pasadena. A density value for elevation corrections was obtained using a least squares method and data obtained with a network of 35 stations in Washington Park. A topographical correction was also made for the San Gabriel Mountains to the north of the area.</p>
<p>The corrected gravity data were used to calculate elevations of the basement along Howard Street, and the resulting basement profile compared with one obtained by a seismograph survey.</p>
<p>Part III:
The properties of various types of waves set up by underwater explosions is discussed from the viewpoint of their application in locating shot points in seismic work carried on over water. The construction of the audio amplifiers and filters used to record these waves is described, together with the results of a preliminary check of their performance.</p>
https://thesis.library.caltech.edu/id/eprint/5989Studies in Acoustic Pulse Propagation
https://resolver.caltech.edu/CaltechETD:etd-06292004-161005
Authors: Spencer, Terry Warren
Year: 1956
DOI: 10.7907/RAV7-NV35
A theoretical study is made of the transient response in two acoustic systems. Each system consists of an ideal fluid in contact with an elastic solid. In one case the interface is plane, in the other case it is cylindrical.
In the plane case it is found that an exact algebraic solution can be obtained on the axis of symmetry. The vertical displacement at axial points is composed of the acoustic, afterflow, and correction terms. In solids for which Poisson's ratio is greater than one third the initial variation of the correction is toward positive values (corresponding to motion directed toward the interface). In solids for which Poisson's ratio is less than one third the initial variation may be either positive or negative depending on the magnitude of the compressional velocity ratio. An interface wave is shown to exist regardless of the choice of elastic parameters. It is found that the reflected wave has a forerunner in the region of the fluid in which the refracted wave is the first arrival.
In the cylindrical case the initial pulse shape is distorted upon reflection. It is found that as the wave approaches the axis of the cylinder the leading edge steepens. If, at the source, the initial slope of the pressure-time curve is finite the amount of steepening is infinite. An exact expresson for the transient response at points off the axis is obtained which can be evaluated by numerical means.
https://thesis.library.caltech.edu/id/eprint/2771I. On the Reflection of Plane Waves by Stratified Systems (Normal Incidence). II. The Determination of Seismic Velocities in Layers with Non-Parallel Interfaces
https://resolver.caltech.edu/CaltechETD:etd-07132004-140721
Authors: Grau, Gérard
Year: 1957
DOI: 10.7907/2AR7-AG54
The purpose of this study is to establish that the reflection of a plane wave (at normal incidence) by a nonhomogeneous layer with properties varying only in the direction of wave propagation may be deduced by a limiting process from the formulae which are valid in the case of discrete homogeneous layers. In this limiting process the number of layers is made to increase without bounds while the thickness of each layer tends to zero in such a way that the total thickness remain constant.
This is done by using the matrix relation which binds the up and down-going wave amplitudes in two layers of a pile of homogeneous layers on top of a semi-infinite homogeneous medium. Then the number of layers is increased as described above and the limit of the matrix relation obtained. It is then verified that the result thus gotten is identical to the quantity obtained by solving the differential equation for the disturbance in a nonhomogeneous layer whose properties are the ones which the discrete case is made to tend to.
A method for calculating velocities in homogeneous isotropic layers and the position of their interfaces from surface reflection seismic measurements is described. The problem is discussed only in the case of parallel strikes. Conditions of applicability are plane interfaces and good lateral correlations.
Also the accuracy of the determination of the velocities and the position of the interfaces depends very much on the velocity, the dip and a distance which gives the position of the interface. One should be careful to estimate in each particular case whether the method may safely be used.https://thesis.library.caltech.edu/id/eprint/2869Thermal Activity and Related Phenomena in Iceland
https://resolver.caltech.edu/CaltechETD:etd-07082004-135901
Authors: Bödvarsson, Gunnar
Year: 1957
DOI: 10.7907/H708-R451
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in the .pdf document.
The thermal activity in Iceland is grouped into two groups, the low-temperature and the high-temperature activity, in accordance with the temperature at the base of the circulation systems. The low-temperature activity includes those thermal areas where this temperature is below 150 [degrees]C. The high-temperature activity includes areas with a higher temperature. The concentration of free CO2 in the spring gases and the concentration of dissolved SiO2 in the thermal water furnish information about the base temperature. The isotope ratios D/H and O18/O16 are indicative of recharge areas and the general pattern of flow. Temperature conditions in near surface layers are studied by the electric resistivity methods. The total heat transported by the low-temperature activity is estimated at 0.2 to [...] cal/sec and by the high-temperature activity at 0.3 to [...] cal/sec. Temperature conditions in 3 non-thermal wells in Iceland are studied and corrected for various effects, mainly the heavy erosion during the Pleistocene. The outward conduction of heat in Iceland appears to be of the order of 3 to [...] cal/sec [...] which is 2.5 to 4 times the normal. The abnormal conduction flow appears to be the main source of energy for the low-temperature activity whereas large volcanic intrusives of recent origin appear to supply the high temperature activity. The abnormal conduction flow ray be caused partially by large magmatic intrusives in the upper 10 to 20 km under Iceland.https://thesis.library.caltech.edu/id/eprint/2829Wave Propagation in a Continuously Stratified Fluid
https://resolver.caltech.edu/CaltechETD:etd-08092004-091454
Authors: Savage, James Crampton
Year: 1957
DOI: 10.7907/SDVS-AN85
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The problem consists of finding the pressure response to a pressure source in an acoustical system of a stratified fluid overlying a rigid surface; a uniform gravitational field of acceleration g is directed normal to the rigid surface. The stratification is to be understood as implying that [...], the gradient of the velocity of sound, and [...], the negative logarithmic gradient of the density, are directed parallel or antiparallel to the gravitational field. The magnitudes of the quantities involved are assumed to be appropriate to the atmosphere of the earth.
The first problem treated assumes [...] and [...] are constant, a situation which would obtain in an isothermal atmosphere. The pressure response exhibits 1) an appreciable phase shift upon reflection from the rigid surface at large angles of incidence, 2) a surface wave, and 3) appreciable distortion of the pulse shape.
The second problem neglects g and [...]. The solution given is asymptotically (high frequency) valid only in regions of the fluid reached by least time rays which have not been refracted through the horizontal. This solution indicates that the time average energy flux propagates along rays which differ from the least time rays by an amount dependent upon the frequency, i.e. such an atmosphere exhibits angular dispersion. Asymptotic expressions are derived for the magnitude of the time average energy flux and for the pressure pulse distortion.
Finally, variations in [...] and [...] are admitted simultaneously with the presence of a gravitational field. The solution is qualitatively the same as that of the preceding problem.https://thesis.library.caltech.edu/id/eprint/3055Section I. An Analytical and Experimental Study of Some Simple Geologic Structures. Section II. Gravity Survey of a Part of the Raymond and San Gabriel Basins, Southern California
https://resolver.caltech.edu/CaltechETD:etd-01272006-094501
Authors: Sanford, Allan Robert
Year: 1958
DOI: 10.7907/HKE2-RP54
<p>SECTION I:</p>
<p>The geologic structures produced by two distributions of applied vertical displacement along the base of a homogeneous layer, (1) a broad curve and (2) a sharp step, were investigated analytically and experimentally. A special form of the general theory of elasticity and scale models (with layers of dry sands and clay) were used for a two dimensional analytical and experimental study of these structures.</p>
<p>Each of the two distributions of applied vertical displacement produce a characteristic fracture pattern in the model experiments. For a broad curve, the fracture pattern is a complex zone of normal faults which taper inward to the axis of the fold and die out at depth. For a sharp step, the fracture pattern is (1) a series of curved reverse faults which start steeply at the base of the layer but intersect the upper surface at low angles (thrusts), and (2) a series of normal faults in the uplifted block near the reverse faults.</p>
<p>The initial fractures in the model experiments, for example the curved reverse faults, can be predicted on the basis of the Mohr fracture criterion and the stress distributions found in the elastic analyses. In addition, the displacement fields obtained in the elastic analyses are good first order approximations of the displacement fields observed in the model experiments.</p>
<p>SECTION II:</p>
<p>A gravity survey (640 stations) was conducted over thirty-six square miles of the alluvium covered portion of the Raymond and San Gabriel basins. Corrections for latitude, elevation, and topography were applied to the gravity data. On the basis of the known surface and sub-surface geology, regional gravity due to deep crustal structure, and gravity due to near surface structure were separated and interpreted independently.</p>
<p>The regional gravity due to deep crustal structure indicates a uniform thickening of the earth's crust to the northeast. If all of the regional gravity is attributed to a density difference of 0.5 c.g.s. at the Mohorovicic discontinuity, the rate of thickening is about 100 meters per kilometer.</p>
<p>The distribution of gravity due to near surface structure shows two steep gradient valleys in the bedrock surface beneath the alluvium in the northern part of the area. The elevation to the floor of these valleys indicates at least 1000 feet of subsidence since the deposition of the alluvium (Upper Pleistocene). The bedrock relief is fairly gentle in the southern part of the area where Tertiary rock lies between bedrock and alluvium. This intermediate layer of Tertiary rock may extend more than a mile north of the Raymond fault. The vertical displacement on the Raymond fault may be 600 feet along one section of the fault in east Arcadia.</p>https://thesis.library.caltech.edu/id/eprint/375Exact Transient Solution of Some Problems of Elastic Wave Propagation
https://resolver.caltech.edu/CaltechETD:etd-02212006-132324
Authors: Flinn, Edward Ambrose
Year: 1960
DOI: 10.7907/QRYY-CD29
Exact solutions are obtained for three problems of progressive elastic wave propagation in bounded media: (1) SH wave propagation from an impulsive point source in an infinite plate; (2) torsional waves in a solid cylinder; (3) radiation from an impulsive source of compressional and of shear waves in an infinite solid plate held between smooth rigid surfaces. The Laplace transform method is used.
Problems (1) and (3) are shown to be closely related. For these problems the solution is expressed both as an infinite series of normal modes and an infinite series of multiple reflections, and it is shown that the two representations of the solution are related by Poisson's summation formula. Solutions are obtained for both a delta-function and a unit function input.
Problem (2) is solved as an infinite series of normal modes for an impulsive shear stress source distributed over a normal section of the cylinder. The case of a point source on the axis of the cylinder is examined in detail.
Problem (3) involves mixed boundary conditions. A relation between the solution of this problem and wave propagation in a free plate is discussed.https://thesis.library.caltech.edu/id/eprint/693