Surface rupturing and triggered slip on nearby faults from the Ridgecrest earthquakes revealed by InSAR

Xiaohua Xu, Lauren A. Ward, Bridget R. Smith-Konter, Chris Milliner, Peng Fang, Yehuda Bock, & David T. Sandwell

Published August 14, 2019, SCEC Contribution #9637, 2019 SCEC Annual Meeting Poster #227

We analyzed repeat-pass Sentinel-1 and ALOS-2 synthetic aperture radar images to measure broad-area surface deformation and high-resolution surface rupturing from the combined July 4-5 2019 Ridgecrest earthquake sequence. Phase gradient maps were constructed to illuminate the fine details of the main rupture as well as triggered slip on remote faults. These maps were used by USGS field crews to plan rapid response ground surveys of the rupture zone and for the deployment of creep meters. Compared to previous events in the Eastern California Shear Zone (e.g. 1992 Landers and 1999 Hector Mine) we found a much more complex set of surface fractures, including orthogonal, synthetic and antithetic faults. Additionally, careful inspection of the phase gradient data revealed evidence of shallow triggered creep along a large section of the Garlock Fault (> 35km). By performing a source inversion using the InSAR line-of-sight deformation and GPS data, we found that these earthquakes yielded a larger shallow slip deficit (~25%) than the Landers (19%) and Hector Mine (5%) events. Using this co-seismic slip model, we computed surface strain and stress change to further understand the cracking and triggered creep. This analysis helps us constraint physical properties of the shallow most crust. By comparing static stress change models to the phase gradient maps, we divided the triggered slip observations into classes of faults where failure is promoted or inhibited, where the later may indicate possible instances of dynamic stress triggering. This distinction may help us quantify the spatial extent of fault surface deformation that is more strongly influenced by static stress change or dynamic stress perturbations.

Key Words
Ridgecrest earthquake sequence, InSAR phase gradient, stress, strain

Citation
Xu, X., Ward, L. A., Smith-Konter, B. R., Milliner, C., Fang, P., Bock, Y., & Sandwell, D. T. (2019, 08). Surface rupturing and triggered slip on nearby faults from the Ridgecrest earthquakes revealed by InSAR . Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes