3-D Velocity Model of the Coachella Valley Determined Using P-Wave First Arrival Times from the Salton Seismic Imaging Project and Local Earthquakes

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

Submitted August 14, 2017, SCEC Contribution #7646, 2017 SCEC Annual Meeting Poster #034

The shallow crustal structure in the Salton Trough has been recognized as the primary source of inaccuracy in the current Southern California Earthquake Center (SCEC) velocity model used for seismic hazard studies. Therefore, we improve the seismic velocities in the Coachella Valley by inverting travel times from explosive shots along with earthquake data. We utilized a set of 48,105 P-wave arrival times from 126 explosive shots in the 2011 Salton Seismic Imaging Project (SSIP) recorded at both the SSIP and Southern California Seismic Network (SCSN) stations. In addition, SCSN station-derived first arrivals from 39,998 local earthquakes with a maximum focal depth of 10 km were incorporated into our inversion to produce a comprehensive 3-D P-wave velocity model for the Coachella Valley. Our improved velocity model has a grid spacing of 1-km and exhibits good resolution (~ 50 rays/cubic km) to a depth of at least 7 km. In the top 3 km, we observe a general pattern in the velocities that reflects the surface geology. One of such features is the elongated trough of low velocities within the valley that corresponds to and is expressed as sediments at the surface. Velocities of ~5.4 km/s or less persist down to a depth of 5 km just north of the Salton Sea, suggesting that basement surface is shallower to the NW and deeper to the SE consistent with gravity modeling (Langenheim et al., 2005). We identify depth-limited areas of higher velocities (~ 6.4 – 6.6 km/s) on the western side of the Coachella Valley, which may represent basement rocks from the Eastern Peninsular Ranges.

Citation
Ajala, R., Persaud, P., Stock, J. M., Fuis, G. S., Hole, J. A., Goldman, M. R., & Scheirer, D. S. (2017, 08). 3-D Velocity Model of the Coachella Valley Determined Using P-Wave First Arrival Times from the Salton Seismic Imaging Project and Local Earthquakes. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology