Insight into deformation adjacent to the San Andreas Fault on the Carrizo Plain, CA:  a field study of Study Lake

Collaborators: Dr. Ramon Arrowsmith (ASU) and Dr. Dallas Rhodes (Humboldt State University)

July 2014

Project Summary: Numerous blind thrust faults trend parallel to the SAF but often only appear at the surface as anticlines. Earthquakes along the SAF, including those along blind thrusts, pose a significant hazard to the population of California. In the past 50 years, displacements along blind thrusts have dominated destructive California earthquakes (1982 New Idria, 1983 Coalinga, 1985 Kettleman Hills, and 1997 Whittier Narrows). Blind thrust faults are hazardous because their subdued surficial expressions make their geometry, seismic history, and potential earthquake magnitude difficult to assess. Investigations of surficial deformation at blind thrust faults are therefore necessary in order to understand the geometry and seismic potential of the faults below. Soda Lake, located in the Carrizo Plain, CA, is an ideal place to study deformation due to blind thrust faulting. The Carrizo Plain is bounded by the San Andreas Fault (SAF) to the east and by the Big Spring thrust fault (BSF) to the west. The abandoned lake floor of Soda Lake is tilted southwest away from the SAF. I hypothesize that tilting of these lake deposits is associated with the activity of a blind thrust (related to the BSF), which is propogating under the Carrizo Plain.

As part of my candidacy comprehensive exams, I completed field work in the summer of 2014 to assess the magnitude and geometry of tilting at Soda Lake in order to assess the geometry of the structure below. I conducted detailed geomorphic transects of Soda Lake and produced high-resolution, 3-D models of the area using Structure from Motion (photogrammetry).  Using field observations, I created geomorphic maps and a proposed geomorphic evolution of Soda Lake. Differential GPS data revealed that lake deposits at Soda Lake dip to the Southwest ~0.422 m/km. Differential GPS data and Structure from Motion imaging remained too dispersed, however, to say anything more substantial about the underlying structure. The Bureau of Land Management has committed to acquiring a full set of images of Soda Lake in order to create a complete DEM using Structure from Motion. For more information about the current status of that data set, please contact Dr. Ramon Arrowsmith (Professor, Arizona State University, School of Earth and Space Exploration).

All images and text on this site © 2016 Kate Leary