11/12/2019 - 12:00pm
Revelle Conference Room (IGPP 4301)
Talk abstract 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. 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). We further produced high-pass filtered phase maps to infer the direction of deformation (left-lateral or right-lateral). 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 static Coulomb stress change for a suite of receiver fault orientations consistent with those exhibiting fractures. Comparing static stress change models to the fracture map, we divided these observations into classes of fractures where failure is promoted or inhibited. We experiment with different friction coefficient and background stress to better explain these features. Preliminary results show that a very low friction for the upper-most crust is supported and dynamic weakening or triggering is required to explain part of the inhibited fractures. 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.
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