Active source tomography in Salton Trough: Geologic insights and application to ground motion prediction

Rasheed Ajala


Date & Time
Online-only seminar via Microsoft Teams

The Salton Trough hosts the southernmost segment of the San Andreas fault that is overdue for a large magnitude earthquake rupture. To better prepare for such an event, we need improved velocity models in the area that characterize the geology better and thus produce more accurate seismic hazard estimates. Using a combination of local earthquakes and active source data from the 2011 Salton Seismic Imaging Project (SSIP), we develop a high-resolution local travel time velocity model in Coachella Valley down to 10 km below sea level. The model shows strong correlations with the surface geology at shallow depths and lateral velocity changes across surface traces of mapped faults and seismicity trends at depth. We map the 3D asymmetric basin of Coachella valley, high-velocity (>6.4 km/s) zones possibly related to Late Cretaceous mylonitic rocks or older inherited basement structures, and a potential unmapped fault zone in Lost Horse Valley. Comparisons between the model and regional community models developed by the Southern California Earthquake Center (SCEC) reveal significant differences in basin geometry and crustal heterogeneity. We smoothly embed our SSIP-derived models for Coachella and Imperial Valleys into the SCEC models to produce hybrid models. Low-frequency seismograms (6 – 30 s) generated from the hybrid models better fit observed waveforms than the SCEC models alone. The hybrid models currently represent the best models in Salton Trough for earthquake hazard assessment and geologic studies.

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