Investigating the Simi-Santa Rosa fault with pre-development high-resolution topography

Brian J. Schrotenboer, Reed J. Burgette, & Katherine M. Scharer

Submitted August 14, 2021, SCEC Contribution #11402, 2021 SCEC Annual Meeting Poster #068

The Simi-Santa Rosa fault (SSRF) bounds the northern edge of the Simi Valley basin in the Western Transverse Ranges, California. GPS velocities measured across this part of the Transverse Ranges show ~6-7 mm/yr of crustal shortening, thought to be accommodated mainly by slip on the Santa Susana fault (SSF) based on published early Pleistocene rates as high as 10 mm/yr. Our recent work suggests the late Quaternary slip rate of the SSF is likely much lower, which motivates better resolving the slip rates of other nearby structures in the footwall of the SSF. A challenge is that much of the SSRF surface trace has been modified by development since the mid-20th century. We are employing a multi-temporal photogrammetry strategy (Time-SIFT, Feurer et al., 2021) to develop a high-resolution model of surface topography using multiple epochs of historic aerial photos. By using this method, we produce a digital elevation model (DEM) of 1928 to 1929 topography of the Simi Valley and Santa Susana Mountains while benefitting from the stronger multi-view photo geometry from other more recent epochs of aerial photography. Analyzing the historic and modern topography enables measurement along geomorphic features and of vertical deformation across the SSRF, which is otherwise challenging to obtain with modern development. Given that the resolution of the historic DEM is ~1 m, which is similar to the resolution of the airborne lidar data available for the area, we can validate the historic DEM against the lidar in undeveloped parts of the region. In an initial field work campaign, we collected charcoal samples from below alluvial surfaces that extend north from the trace of the SSRF, onto the footwall of the SSF. Combining the detailed topographic mapping on the pre-development DEM, field interpretation and geochronology, we aim to characterize late Quaternary sense of motion and slip rate along the SSRF.

Key Words
Photogrammetry fault slip rate

Schrotenboer, B. J., Burgette, R. J., & Scharer, K. M. (2021, 08). Investigating the Simi-Santa Rosa fault with pre-development high-resolution topography. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology