Finite-Source Modeling for Parkfield and Anza Earthquakes

Abstract:

Repeating earthquakes occur in the vicinity of creeping sections along the Parkfield section of the San Andreas fault (Nadeau et al., 1995) and the Anza section of the San Jacinto fault (Taira, 2013). Uilizing an empirical Green’s function (eGF) approach for both the Parkfield and Anza events, we are able to conduct a comparative study of the resulting slip distributions and source parameters to examine differences in the scaling of fault dimension, average slip, and peak-slip with magnitude. Following the approach of Dreger et al. (2007), moment rate functions (MRFs) are obtained at each station for both Parkfield and Anza earthquakes using a spectral domain deconvolution approach where the complex spectrum of the eGF is divided out of the complex spectrum of the target event. Spatial distributions of fault slip are derived by inverting the MRFs, and the coseismic stress change is computed following the method of Ripperger and Mai (2004). Initial results are based on the analysis of several Parkfield target events ranging in magnitude from Mw1.8 to 6.0 (Dreger et al., 2011) and a Mw4.7 Anza event. Parkfield peak slips are consistent with the Nadeau and Johnson (1998) tectonic loading model, while average slips tend to scale self-similarly. Results for the Anza event show very high peak and average slips, in exceedance of 50 cm and 10 cm respectively. Directivity for this event is in the northwest direction, and preliminary sensitivity analyses suggest that the rupture velocity is near the shear wave velocity and the rise time is short (~0.03 sec). Multiple eGFs for the Anza event have been evaluated and the results appear robust.