Progress towards deriving the three-dimensional coseismic deformation field along the White Wolf fault during the Mw ~7.3 1952 Kern County earthquake

Alexandra E. Hatem, James F. Dolan, & Chris W. Milliner

Submitted August 15, 2016, SCEC Contribution #6765, 2016 SCEC Annual Meeting Poster #017

We present preliminary results of our efforts to constrain coseismic surface deformation during the Mw~7.3 1952 Kern County earthquake. We are using a modified workflow to difference point clouds derived from legacy air photos taken before and after the July 21 event, with the pre-event survey on May 23, 1952 and the post-event survey spanning August to September, 1952. Because no camera parameters were recorded during the aerial photo surveys, we cannot use change detection algorithms (e.g., COSI-Corr) that have previously been used to measure coseismic surface deformation in other earthquakes. Instead, we create point clouds from the unreferenced and uncalibrated pre- and post-event images using Agisoft Photoscan. We georeference the air photos using a modern (Landsat) image, which enables the creation of a georeferenced point cloud, as well as a digital surface model and orthorectified, mosaicked image. Pre- and post-earthquake georeferenced point clouds are then differenced using the iterative closest point (ICP) algorithm within Cloud Compare. This allows us to derive the x, y, and z cloud-to-cloud distances, and hence the cosesimic deformation field. We have conducted a test of the workflow on the eastern part of the Kern County rupture along sections of the White Wolf fault where surface rupture was documented by Bulwada and St. Armand (1955). We observe primarily thrust displacement (south-side-up), and in some instances we detect near-field warping on the order of 1-4 meters. Creating a complete, three-dimensional surface deformation field along this rupture will provide a much-needed data set of ground deformation during a large-magnitude earthquake generated by rupture of a partially blind thrust fault that exhibits multiple senses of displacement. The deformation field associated with the 1952 White Wolf fault event will provide a useful analog for similar deformation in future large-magnitude earthquakes generated by the major blind thrust faults beneath metropolitan Los Angeles, including the Puente Hills and Compton blind thrust faults.

Key Words
1952 Kern County earthquake; White Wolf fault; image correlation; blind thrust faults

Citation
Hatem, A. E., Dolan, J. F., & Milliner, C. W. (2016, 08). Progress towards deriving the three-dimensional coseismic deformation field along the White Wolf fault during the Mw ~7.3 1952 Kern County earthquake. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)