GPS Measurements of Crustal Deformation in San Andreas Fault System
Chia-Chu Yang
Abstract
The California is a deformed orogenic belt resulting from the collage and collision of blocks of oceanic and continental affinities. In the California, there is a typical fault over here that named the San Andreas Fault.The San Andreas Fault is a geological fault that runs a length of roughly 800 miles (1,300 km) through western and southernCalifornia in the United States. The fault, a right-lateral strike-slip fault, marks a transform (or sliding) boundary between the Pacific Plate and the North American Plate.
We develop a two-dimensional boundary element earthquake cycle model including deep interseismic creep on vertical strike-slip faults in an elastic lithosphere coupled to a viscoelastic asthenosphere. The model is applied to the GPS contemporary velocity field across the CarrizoPlain and northern San FranciscoBay segments of the San Andreas fault, as well as triangulation measurements of postseismic strain following the 1906 San Francisco earthquake. Interseismic deformation measurements are generally interpreted in terms of steady slip on buried elastic dislocations. Although such models often yield slip rates that are in reasonable accord with geologic observations, they are inconsistent with our expectation of fault structure at depth, and cannot explain transient postseismic deformation following large earthquakes. An alternate two-dimensional model of repeating earthquakes that break an elastic plate of thickness H, overlying a Maxwell viscoelastic half-space with relaxation time tR (Savage and Prescott, 1978) involves five parameters; H, tR, t, T, and , where t is the time since the last quake, T is the earthquake repeat time, and s is the slip rate. Many parts of the San Andreas fault (SAF) system involve multiple parallel faults, which further increases the number of parameters to be estimated. All hope is not lost, however, if we make use of geologic constraints on slip rate, as well as the measured time-dependent strain following the 1906 earthquake, in addition to the present-day spatial distribution of deformation rate.
Previous analysis of these data, using conventional viscoelastic coupling models without stress-driven creep [Segall, 2002], shows that it is necessary to invoke different lithosphere-asthenosphere rheology in northern and southern California in order to explain the data. We show that with deep stress-driven interseismic creep on the San Andreas fault, the data can be explained with the same rheology for northern and southern California.
References
J. R. Murray, P. Segall, P. Cervelli, W. Prescott and J. Svarc(2001), Inversion of GPS data for spatially variable slip-rate on the San Andreas Fault near Parkfield, CA, J. Geophys. Res., VOL. 28, NO. 2, PAGES 359-362, JANUARY 15,
K. M. Johnson and P. Segall(2004), Viscoelastic earthquake cycle models with deep stress-driven creep along the San Andreas fault system, J. Geophys. Res., VOL. 109, B10403, doi:10.1029/2004JB003096
P. Segall(2002), Integrating Geologic and Geodetic Estimates of Slip Rate on the San Andreas Fault System International Geology Review, Vol. 44, 2002, p. 62–82.