SCEC Award Number 11090 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Geometry of fault slip zones at depth from quantitative analysis of seismic catalogs
Investigator(s)
Name Organization
Yehuda Ben-Zion University of Southern California
Other Participants PhD student, Yaman Ozakin
SCEC Priorities A4, A10, A3 SCEC Groups USR, LAD, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Studies under this project attempt to develop a quantitative method for estimating the geometry of active fault zones at seismogenic depth using typical entries of earthquake catalogs. In contrast to prior methods that make various assumptions on geometrical properties of the structure (e.g. sets of planes or fractal network), our method does not presuppose any shape. Each recorded earthquake is assigned a Gaussian likelihood function with central coordinates and standard deviations in different directions corresponding to the hypocenter location and errors. The likelihood function is given a weight corresponding to the event size. The sum of the likelihoods of all earthquakes reported for a given region, with normalization to account for different event numbers in different locations, provides a likelihood field for the occurrence of slip patches in the examined volume. High contiguous regions of likelihood values represent large fault zone sections. Synthetic catalogs are used to develop and test normalization methods that account for typical spatio-temporal variations of seismicity, and to identify characteristic likelihood shapes corresponding to typical types of structural heterogeneities (e.g. stepovers, parallel faults). In the present application the method is applied to estimate geometrical properties of the seismicity in the San Jacinto fault zone environment.
Intellectual Merit At present there is scant information on geometrical properties of fault interfaces and slip zones at depth, where the bulk of the elastic strain energy is stored and released, and there is no quantitative method with general potential applicability for obtaining such information.
Seismic catalogs are both the most readily available and potentially highest-resolution sources of information on geometrical properties of fault slip patches at depth. In California and other tectonically-active places, where seismic network have been operating for tens of years, the catalogs have entries on thousands to tens of thousands of hypocenters and slip patches of various sizes in regional and local fault zone environments. In this study we develop a simple quantitative method that uses these entries, along with their associated variances, to calculate a likelihood function on the geometry of the slip patches in the volume containing the events. We make no apriori assumptions about the shape of the fault zone (e.g. planarity)
Broader Impacts Geometrical fault zone heterogeneities have fundamental effects on many aspects of earthquake physics and seismic hazard.
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