FAULT MODEL FOR PRESEISMIC DEFORMATION AT PARKFIELD, CALIFORNIA

Citation
Wd. Stuart et Te. Tullis, FAULT MODEL FOR PRESEISMIC DEFORMATION AT PARKFIELD, CALIFORNIA, J GEO R-SOL, 100(B12), 1995, pp. 24079-24099
Citations number
76
Categorie Soggetti
Geochemitry & Geophysics
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
ISSN journal
21699313 → ACNP
Volume
100
Issue
B12
Year of publication
1995
Pages
24079 - 24099
Database
ISI
SICI code
2169-9313(1995)100:B12<24079:FMFPDA>2.0.ZU;2-V
Abstract
We construct an earthquake instability model to estimate precursory fa ulting and ground deformation before the next moderate (M 5.5-6) earth quake on the San Andreas fault near Parkfield, California. The quasi-s tatic model simulates fault slip, fault shear stress, and ground defor mation for all stages of repeated earthquake cycles. Unstable slip, wh ich is the analog of a moderate Parkfield mainshock, is caused by over all failure of a postulated strong area or patch of the fault zone, Th e brittle patch and surrounding weaker viscous fault are defined by th e sign of a spatially varying coefficient of a slip rate dependent fau lt law. Stable failure of the patch leading up to mainshock failure ca uses slip rate to increase at depth. Amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current e arthquake cycle at Parkfield, starting just after the 1966 mainshock, in two ways. In the first way we vary parameter values in a sequence o f simulations so as to find the simulation giving best agreement with locations, moments, and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock. In the second way we assign values of most paramet ers from laboratory friction experiments and a temperature-depth profi le inferred from heat flow data. Overall agreement between model resul ts and observations is comparable for the two methods. In all simulati ons, preseismic deformation anomalies arise from slip rate increase ne ar the model earthquake focus and start several years or less before i nstability. Preseismic anomalies in surface fault creep and line lengt h are always too small to detect in current measurements. However, for some simulations constrained mainly by field data the predicted anoma lies in borehole dilatation are large enough to detect.