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A Structural V_P Model of the Salton Trough, California, and Its Implications for Seismic Hazard

¹ Department of Earth and Planetary Sciences
Harvard University
20 Oxford Street
Cambridge, Massachusetts 02138
 (P.L., J.H.S.)
² Seismological Laboratory
California Institute of Technology
1200 E. California Blvd.
Pasadena, California 91125
 (Q.L., J.T.)

We present a high-resolution, three-dimensional P-wave seismic velocity model of the sedimentary basin in the Salton Trough, southern California, and use the model for spectral-element method (SEM) wave propagation and ground- motion simulations to quantitatively assess seismic hazard in the region. The basin geometry is defined by a surface representing the top of crystalline basement, which was constrained by seismic refraction profiles and free-air gravity data. Sonic logs from petroleum wells in the Imperial Valley and isovelocity surfaces defined by seismic refraction studies were used to define P-wave velocity within the sedimentary basin as a function of two variables:(1) absolute depth and (2) depth of the underlying crystalline basement surface (CBS). This velocity function was used to populate cells of a three-dimensional spatial array (voxet) defining the P-wave velocity structure in the basin. The new model was then resampled in a computational mesh used for earthquake wave propagation and strong ground motion simulations based upon the SEM (Komatitsch et al., 2004). Simulation of the 3 November 2002 M_w 4.2 Yorba Linda earthquake demonstrates that the new model provides accurate simulation of strong ground motion amplification effects in the Salton Trough sedimentary basin, offering substantial improvements over previous models. A hypothetical M_w 7.9 earthquake on the southern San Andreas fault was then simulated in an effort to better understand the seismic hazard associated with the basin structure. These simulations indicate that great amplification will occur during large earthquakes in the region due to the low seismic velocity of the sediments and the basin shape and depth.

Online material: Details of the gravity modeling techniques.