The July 2019 Ridgecrest seismic sequence: multi-sensor DInSAR data and coseismic source modeling

The Ridgecrest sequence (RS) started on the 4 July 2019 and it has included one strong (M6.4) and one major earthquake (M7.1, on the 5 July) that struck for at least 35 km from the first epicenter, towards the northwest. There are not only these recent quakes near Ridgecrest, in fact, since 1932, 31 events of M4.0 or greater struck in this area: the largest historic one was M5.8 (1995) while the most recent historic event was M4.1 (2011). Actually one of the strongest quakes ever felt in the state occurred in the shear zone north of the recent epicenters, when a M7.9 destroyed the town of Lone Pine in 1872.

The RS area includes a previously unmapped fault whose slip generated surface ruptures and damaged homes and infrastructures; although the remote area was known to be seismically active and geologically complex, the earthquakes were sprinkled around a pair of neighbouring geologic faults that were not specifically known about before. The M6.4 event ruptured the NE-trending left-lateral cross fault over a distance of approximately 9.5 km within the Little Lake fault zone, on the west of Searles Valley, while the M7.1 event occurred on the NW-trending fault at a depth of 8.0 km; the rupture, occurred bilaterally to the NW and SE over an approximate length of 50 km, was right-lateral strike-slip.

In order to investigate the source geometry and kinematics we exploit seismological, Global Positioning System, and Sentinel-1 and Alos2 differential interferometric synthetic aperture radar coseismic measurements. Preliminary inversion results show that the slip reached a peak of > 5 m at a depth of about 5 km. Moreover, in order to better understand the deformation behaviour of the examined area, we analyse the pre-seismic condition that preceded the RS. In this context, we also exploit the computed Sentinel-1 DInSAR deformation time series from March 2015 to June 2019 computed through the Small BAseline Subset (SBAS) approach.