Crustal Deformation Before, During and After the 2019 Ridgecrest Earthquakes from Campaign and Continuous GNSS Data

Session: Observations From the 2019 Ridgecrest Earthquake Sequence
Type: Oral
Date: 4/28/2020
Time: 03:00 PM
Room: 115
Description: 

The 2019 Ridgecrest earthquakes occurred in an area of the northern Mojave Desert that was studied extensively with campaign GNSS in the late 1990s and early 2000s. We started a program of updating these measurements in early 2019, just 5 months before the July 4th, M6.4 earthquake. Our response to the event was to reoccupy five campaign sites to the west and south of the rupture, all within 30 km distance of the rupture and within 24 hours after the M6.4 foreshock. Our GNSS stations were operational 10 hours before, and remained so after, the M7.1 mainshock that occurred on July 6th (Universal Time), thus we can distinguish coseismic displacements for the two events. Around 25 additional temporary stations were installed by multiple groups in the days that followed, and the majority of these have remained in operation semi-continuously for the six months since.

We present here updated results from the processing of the GNSS campaign data, along with over 50 continuous GNSS stations operating in the region. We resolve a total interseismic deformation rate of ~12 mm/yr across the Eastern California-Walker Lane shear zone; models suggest as much as half of that could be localized on the Airport Lake fault zone near Ridgecrest. Coseismic displacements from the two events suggest that the two principal faults involved could be cross-cutting, with each showing resolved slip either side of their intersection. Near-field GNSS displacements to the northeast of the two ruptures favor secondary right-lateral slip on a NW-trending structure in the first, M6.4 event, consistent with the early aftershock pattern. Finally, the near-field transient surface velocity following the events is significantly slower than that associated with other recent events in California (Parkfield, South Napa) with a maximum amplitude of 4 cm in the first three months, and a pattern of motion consistent with afterslip on the ruptured faults and their downdip extensions.

Presenting Author: Gareth J. Funning

Authors