SAR Imaging of the Coseismic and Early Postseismic Deformation from the 2019 Mw 7.1 and Mw 6.4 Ridgecrest Earthquakes in California

Eric J. Fielding, Oliver Stephenson, Minyan Zhong, Simran S. Sangha, Cunren Liang, Mong-Han Huang, Zhen Liu, Sang-Ho Yun, Mark Simons, & Benjamin A. Brooks

Published August 15, 2019, SCEC Contribution #9883, 2019 SCEC Annual Meeting Poster #231

We analyzed synthetic aperture radar (SAR) images from Copernicus Sentinel-1A and -1B satellites operated by the European Space Agency and the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by Japanese Aerospace Exploration Agency for the 4 July 2019 Mw 6.4 and 5 July Mw 7.1 Ridgecrest Earthquakes. Caltech-Jet Propulsion Laboratory Advanced Rapid Imaging and Analysis (ARIA) project automatically processed Sentinel-1 InSAR and manually processed ALOS InSAR products that were delivered to the US and California Geological Surveys to aid field response. We integrate geodetic measurements for the three-dimensional vector field of coseismic surface deformation for the two events and measure the early postseismic deformation, using SAR data from Sentinel-1 and ALOS-2 satellites. We combine less precise large-scale displacements from SAR images by pixel offset tracking or matching, including the along-track component, with the more precise SAR interferometry (InSAR) measurements in the radar line-of-sight direction and intermediate-precision along-track InSAR to estimate all three components of the surface displacement for the two events together. InSAR coherence and coherence change maps the surface disruptions due to fault ruptures reaching the surface. Large slip in the Mw 6.4 earthquake was on a NE-striking fault that intersects with the NW-striking fault that was the main rupture in the Mw 7.1 earthquake. The main fault bifurcates towards the southeast ending 3 km from the Garlock Fault. The Garlock fault had triggered slip of about 15 mm along a short section directly south of the main rupture. About 3 km NW of the Mw 7.1 epicenter, the surface fault separates into two strands that form a pull-apart with about 1 meter of down-drop. Further NW is a wide zone of complex deformation. We image postseismic deformation with InSAR data and point measurements from new GPS stations installed by the USGS. Initial analysis of the first InSAR measurements indicates the pull-apart continued dropping in the first weeks and the main fault had substantial afterslip close to the epicenter where the largest coseismic slip occurred. Sentinel-1 6-day repeats enable rapid postseismic mapping. Slip on a NE-striking fault near the northern end of the main rupture in the first weeks, in the same zone as large and numerous aftershocks along NE-striking and NW-striking trends shows complex deformation.

Key Words
InSAR, SAR pixel offsets, coseismic, postseismic, Ridgecrest

Citation
Fielding, E. J., Stephenson, O., Zhong, M., Sangha, S. S., Liang, C., Huang, M., Liu, Z., Yun, S., Simons, M., & Brooks, B. A. (2019, 08). SAR Imaging of the Coseismic and Early Postseismic Deformation from the 2019 Mw 7.1 and Mw 6.4 Ridgecrest Earthquakes in California. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes