HR: 1340h
AN: S53A-0193    [Abstracts]
TI: Compactness vs. Smoothness: Methods for regularizing fault slip inversions with application to subduction zone earthquakes.
AU: * Lohman, R B
EM: fisheggs@gps.caltech.edu
AF: Woods Hole Oceanographic Institution, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Simons, M
EM: simons@gps.caltech.edu
AF: California Institution of Technology, MSC 252-21 1200 E. California Blvd, Pasadena, CA 91125 United States
AB: We examine inversions of geodetic data for fault slip and discuss how inferred results are affected by choices of regularization. The final goal of any slip inversion is to enhance our understanding of the dynamics governing fault zone processes through kinematic descriptions of fault zone behavior at various temporal and spatial scales. Important kinematic observations include ascertaining whether fault slip is correlated with topographic and gravitational anomalies, whether coseismic and postseismic slip occur on complementary or overlapping regions of the fault plane, and how aftershock distributions compare with areas of coseismic and postseismic slip. Fault slip inversions are generally poorly-determined inverse problems requiring some sort of regularization. Attempts to place inversion results in the context of understanding fault zone processes should be accompanied by careful treatment of how the applied regularization affects characteristics of the inferred slip model. Most regularization techniques involve defining a metric that quantifies the solution "simplicity". A frequently employed method defines a "simple" slip distribution as one that is spatially smooth, balancing the fit to the data vs. the spatial complexity of the slip distribution. One problem related to the use of smoothing constraints is the "smearing" of fault slip into poorly-resolved areas on the fault plane. In addition, even if the data is fit well by a point source, the fact that a point source is spatially "rough" will force the inversion to choose a smoother model with slip over a broader area. Therefore, when we interpret the area of inferred slip we must ask whether the slipping area is truly constrained by the data, or whether it could be fit equally well by a more spatially compact source with larger amplitudes of slip. We introduce an alternate regularization technique for fault slip inversions, where we seek an end member model that is the smallest region of fault slip that can explain the data. In these "compact slip" inversions, we define model simplicity as the spatial compactness of the fault slip distribution. Our measure of compactness allows for multiple regions of slip when they are required by the data. We compare inversions using compactness and smoothness as regularization criteria in several synthetic scenarios. We also apply the compact slip technique to coseismic and postseismic deformation associated with the 1995 Mw 8.1 Antofagasta, Chile, and 2003 Mw 8.1 Tokachi-Oki, Japan, subduction zone earthquakes, using InSAR and GPS data.
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 1200 GEODESY AND GRAVITY
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
SC: Seismology [S]
MN: 2004 AGU Fall Meeting