CaltechAUTHORS: Article
https://feeds.library.caltech.edu/people/Jordan-T-H/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 05 Nov 2024 19:07:08 -0800Optimal Solutions to a Linear Inverse Problem in Geophysics
https://resolver.caltech.edu/CaltechAUTHORS:JORpnas71
Year: 1971
This paper is concerned with the solution of the linear system obtained in the Backus-Gilbert formulation of the inverse problem for gross earth data. The theory of well-posed stochastic extensions to ill-posed linear problems, proposed by Franklin, is developed for this application. For given estimates of the statistical variance of the noise in the data, an optimal solution is obtained under the constraint that it be the output of a prescribed linear filter. Proper specification of this filter permits the introduction of information not contained in the data about the smoothness of an acceptable solution. As an example of the application of this theory, a preliminary model is presented for the density and shear velocity as a function of radius in the earth's interior.https://resolver.caltech.edu/CaltechAUTHORS:JORpnas71Earth Structure from Free Oscillations and Travel Times
https://resolver.caltech.edu/CaltechAUTHORS:20150407-112143304
Year: 1973
An extensive set of reliable gross Earth data has been inverted to obtain a new
estimate of the radial variations of seismic velocities and density in the Earth. The
basic data set includes the observed mass and moment of inertia, the averaged periods
of free oscillation, and five new sets of differential travel-time data. The eigenperiod
data was drawn mainly from the Dziewonski-Gilbert study. The differential travel-time
data consists of the times of PcP-P, ScS-S, P_(AB)'-P_(DF)' and P_(BC)'-P_(DF)'.
These data were inverted using the linear estimation algorithm described by Jordan
(PhD Thesis, California Institute of Technology, 1972). A simple but realistic starting
model was constructed based on a number of physical assumptions, such as requiring
the Adams-Williamson relation to hold in the lower mantle and core. By using
baselifie-insensitive differential travel times and averaged eigenperiods, a considerable
improvement in both the quality of the fit and the resolving power has been realized.
The spheroidal and torodial data are fit on the average to 0.04 and 0.08 per cent,
respectively. The final model, designated model B1, also agrees with Rayleigh and
Love wave phase and group velocity data.https://resolver.caltech.edu/CaltechAUTHORS:20150407-112143304Earth Structure from Free Oscillations and Travel Times
https://resolver.caltech.edu/CaltechAUTHORS:20141118-143403005
Year: 1974
DOI: 10.1111/j.1365-246X.1974.tb03648.x
An extensive set of reliable gross Earth data has been inverted to obtain a new estimate of the radial variations of seismic velocities and density in the Earth. The basic data set includes the observed mass and moment of inertia, the average periods of free oscillation (taken mainly from the Dziewonski-Gilbert study), and five new sets of differential travel-time data. The differential travel-time data consists of the times of PcP-P and ScS-S, which contain information about mantle structure, and the times of P′_(AB) - P′_(DF) and P′_(BC)-P′_(DF) which are sensitive to core structure. A simple but realistic starting model was constructed using a number of physical assumptions, such as requiring the Adams-Williamson relation to hold in the lower mantle and core. The data were inverted using an iterative linear estimation algorithm. By using baseline-insensitive differential travel times and averaged eigenperiods, a considerable improvement in both the quality of the fit and the resolving power of the data set has been realized. The spheroidal and toroidal data are fit on the average to 0·04 and 0·08 per cent, respectively. The final model, designated model B1, also agrees with Rayleigh and Love wave phase and group velocity data.
The ray-theoretical travel times of P waves computed from model B1 are about 0·8s later than the 1968 Seismological Tables with residuals decreasing with distance, in agreement with Cleary & Hales and other recent studies. The computed PcP, PKP, and PKiKP times are generally within 0·5 s of the times obtained in recent studies. The travel times of S computed from B1 are 5–10 s later than the Jeffreys-Sullen Tables in the distance range 30° to 95°, with residuals increasing with distance. These S times are in general agreement with the more recent data of Kogan, Ibrahim & Nuttli, Lehmann, Cleary, and Bolt et al.
Model B1 is characterized by an upper mantle with a high, 4·8 km s^(−1), S_n velocity and a normal, 3·33 g cm^(−3), density. A low-velocity zone for S is required by the data, but a possible low-velocity zone for compressional waves cannot be resolved by the basic data set. The upper mantle transition zone contains two first-order discontinuities at depths of 420 km and 671 km. Between these discontinuities the shear velocity decreases with depth. The radius of the core, fixed by PcP-P times and previous mode inversions, is 3485 km, and the radius of the inner core-outer core boundary is 1215 km. There are no other first-order discontinuities in the core model. The shear velocity in the inner core is about 3·5 km s^(−1).https://resolver.caltech.edu/CaltechAUTHORS:20141118-143403005Numerical Modelling of Instantaneous Plate Tectonics
https://resolver.caltech.edu/CaltechAUTHORS:20141118-145318337
Year: 1974
DOI: 10.1111/j.1365-246X.1974.tb00613.x
Assuming lithospheric plates to be rigid, we systematically invert 68 spreading rates, 62 fracture zones trends and 10^6 earthquake slip vectors simultaneously to obtain a self-consistent model of instantaneous relative motions for eleven major plates. The inverse problem is linearized and solved iteratively by a maximum likelihood procedure. Because the uncertainties in the data are small, Gaussian statistics are shown to be adequate. The use of a linear theory permits (1) the calculation of the uncertainties in the various angular velocity vectors caused by uncertainties in the data, and (2) quantitative examination of the distribution of information within the data set.
The existence of a self-consistent model satisfying all the data is strong justification of the rigid plate assumption. Slow movement between North and South America is shown to be resolvable.
We then invert the trends of 20 linear island chains and aseismic ridges under the assumptions that they represent the directions of plate motions over a set of hot spots fixed with respect to each other. We conclude that these hot spots have had no significant relative motions in the last 10 My.https://resolver.caltech.edu/CaltechAUTHORS:20141118-145318337Comparisons Between Seismic Earth Structures and Mantle Flow Models Based on Radial Correlation Functions
https://resolver.caltech.edu/CaltechAUTHORS:20150123-122803275
Year: 1993
DOI: 10.1126/science.261.5127.1427
Three-dimensional numerical simulations were conducted of mantle convection in which flow through the transition zone is impeded by either a strong chemical change or an endothermic phase change. The temperature fields obtained from these models display a well-defined minimum in the vertical correlation length at or near the radius where the barrier is imposed, even when the fields were filtered to low angular and radial resolutions. However, evidence for such a feature is lacking in the shear-velocity models derived by seismic tomography. This comparison suggests that any stratification induced by phase or chemical changes across the mid-mantle transition zone has a relatively small effect on the large-scale circulation of mantle material.https://resolver.caltech.edu/CaltechAUTHORS:20150123-122803275Broadband simulations for M_w 7.8 southern San Andreas earthquakes: Ground motion sensitivity to rupture speed
https://resolver.caltech.edu/CaltechAUTHORS:20090701-151932462
Year: 2008
DOI: 10.1029/2008GL035750
Using the high-performance computing resources of the Southern California Earthquake Center, we simulate broadband (0–10 Hz) ground motions for three M_w 7.8 rupture scenarios of the southern San Andreas fault. The scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0.96, 0.89, and 0.84 times the local shear wave velocity. Consistent with previous simulations, a southern hypocenter efficiently channels energy into the Los Angeles region along the string of basins south of the San Gabriel Mountains. However, we find the basin ground motion levels are quite sensitive to the prescribed rupture speed, with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15%. These results have important implications for estimating seismic hazards in Southern California and emphasize the need for improved understanding of earthquake rupture processes.https://resolver.caltech.edu/CaltechAUTHORS:20090701-151932462Operational Earthquake Forecasting: Some Thoughts on Why and How
https://resolver.caltech.edu/CaltechAUTHORS:20100719-113818032
Year: 2010
DOI: 10.1785/gssrl.81.4.571
The goal of operational earthquake forecasting is to provide the public with authoritative information on the time dependence of regional seismic hazards.https://resolver.caltech.edu/CaltechAUTHORS:20100719-113818032Reply to 'A Second Opinion on "Operational Earthquake Forecasting: Some Thoughts on Why and How," by Thomas H. Jordan and Lucile M. Jones,' by Stuart Crampin
https://resolver.caltech.edu/CaltechAUTHORS:20110328-142809288
Year: 2011
DOI: 10.1785/gssrl.82.2.231
In folklore, a "silver bullet" is an effective weapon against were-wolves and witches. In earthquake prediction, a silver bullet is a diagnostic precursor—a signal observed before an earthquake that indicates with high probability the location, time, and magnitude of the impending event (Jordan 2006). In his comment, Crampin (2010) claims that shear-wave splitting (SWS) observations provide a silver bullet. He asserts that seismology is thus capable of raising earthquake forecasting out of the low-probability environment to which we assigned it in our recent opinion piece (Jordan and Jones 2010).https://resolver.caltech.edu/CaltechAUTHORS:20110328-142809288Unified Structural Representation of the southern California crust and upper mantle
https://resolver.caltech.edu/CaltechAUTHORS:20150409-151104225
Year: 2014
DOI: 10.1016/j.epsl.2015.01.016
We present a new, 3D description of crust and upper mantle velocity structure in southern California implemented as a Unified Structural Representation (USR). The USR is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity (Vp, Vs) measurements and incorporates the locations and displacement of major fault zones that influence basin structure. These basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure, which were subsequently iterated and improved using 3D waveform adjoint tomography. A geotechnical layer (GTL) based on Vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component. The resulting model provides a detailed description of the structure of the southern California crust and upper mantle that reflects the complex tectonic history of the region. The crust thickens eastward as Moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust. Deep sedimentary basins and underlying areas of thin crust reflect Neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late Pliocene. To illustrate the impact of this complex structure on strong ground motion forecasting, we simulate rupture of a proposed M 7.9 earthquake source in the Western Transverse Ranges. The results show distinct basin amplification and focusing of energy that reflects crustal structure described by the USR that is not captured by simpler velocity descriptions. We anticipate that the USR will be useful for a broad range of simulation and modeling efforts, including strong ground motion forecasting, dynamic rupture simulations, and fault system modeling. The USR is available through the Southern California Earthquake Center (SCEC) website (http://www.scec.org).https://resolver.caltech.edu/CaltechAUTHORS:20150409-151104225The Potential Uses of Operational Earthquake Forecasting
https://resolver.caltech.edu/CaltechAUTHORS:20160413-074847668
Year: 2016
DOI: 10.1785/0220150174
This article reports on a workshop held to explore the potential uses of operational earthquake forecasting (OEF). We discuss the current status of OEF in the United States and elsewhere, the types of products that could be generated, the various potential users and uses of OEF, and the need for carefully crafted communication protocols. Although operationalization challenges remain, there was clear consensus among the stakeholders at the workshop that OEF could be useful.https://resolver.caltech.edu/CaltechAUTHORS:20160413-074847668