11/29/2017 - Southward from the San Andreas Fault: Active tectonics, buried basins, and magmatism


12:00 PM - 12:50 PM
Geology 1707

Presented By:
Joann Stock - Caltech


The Salton Trough and Imperial Valley contain pull-apart basins formed by the on-going oblique extension between the Pacific and North America plates, where new crust is being formed along the plate boundary. Much of the plate boundary slip is distributed along the San Andreas and San Jacinto Fault systems, heading southward to a complex set of connections with the Imperial fault and other faults in Mexico. To better understand the structure in this region, we conducted an active source seismic survey (the 2011 Salton Seismic Imaging Project, or SSIP) using explosions in shallow boreholes to derive the crustal structure and fault orientations. This talk will highlight some recently published results from the SSIP and other geological studies, as well as summarize observations from Mexico about the faulting and basin history south of the border. Velocity models and geological interpretations of the crust beneath the Salton Sea indicate that there is a layer of new mafic crust beneath the lowest part of the basin, which is not detected farther south in the Imperial Valley or in the Mexicali Valley. The 3D seismic velocity models also reinforce the correlation of some NE-trending seismicity lineaments with major structural boundaries. These results have important implications for how this part of the Pacific-North America plate boundary evolved, as well as for societal concerns such as earthquake shaking in the LA Basin and future ground ruptures in the Mexicali Valley.

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