Three‐Dimensional Basin and Fault Structure From a Detailed Seismic Velocity Model of Coachella Valley, Southern California.

Ajala, Rasheed; Persaud, Patricia; Stock, Joann M.; Fuis, Gary S.; Goldman, Mark; Scheirer, Daniel; Hole, John A.

The Coachella Valley in the northern Salton Trough is known to produce destructive earthquakes, making it a high seismic hazard area. Knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region. We simultaneously inverted first P wave travel times from the Southern California Seismic Network (39,998 local earthquakes) and explosions (251 land/sea shots) from the 2011 Salton Seismic Imaging Project to obtain a 3‐D seismic velocity model. Earthquakes with focal depths ≤10 km were selected to focus on the upper crustal structure. Strong lateral velocity contrasts in the top ~3 km correlate well with the surface geology, including the low‐velocity (<5 km/s) sedimentary basin and the high‐velocity crystalline basement rocks outside the valley. Sediment thickness is ~4 km in the southeastern valley near the Salton Sea and decreases to <2 km at the northwestern end of the valley. Eastward thickening of sediments toward the San Andreas fault within the valley defines Coachella Valley basin asymmetry. In the Peninsular Ranges, zones of relatively high seismic velocities (~6.4 km/s) between 2‐ and 4‐km depth may be related to Late Cretaceous mylonite rocks or older inherited basement structures. Other high‐velocity domains exist in the model down to 9‐km depth and help define crustal heterogeneity. We identify a potential fault zone in Lost Horse Valley unassociated with mapped faults in Southern California from the combined interpretation of surface geology, seismicity, and lateral velocity changes in the model. Key Points: Low P wave velocities in our model characterize a detailed, 3‐D asymmetric Coachella Valley basinThe 3‐D basin shape and Z2.5 surface produced in this study are important for improving seismic hazard estimates in Southern CaliforniaWe identify a potential fault zone in Lost Horse Valley currently unassociated with mapped faults in Southern California

COACHELLA Valley (Calif.); SEISMIC wave velocity; EARTHQUAKES; CRUST of the earth; SEDIMENTARY basins

Journal of Geophysical Research. Solid Earth, 2019, Vol 124, Issue 5, p4728

2169-9313

Academic Journal

10.1029/2018JB016260