Rupture History of the July 4 and July 6 2019 Ridgecrest Earthquakes
Abstract
On July 4 and 6, 2019, M6.4 and M7.0 earthquakes struck the Searles Valley region of the southern Owens Valley, approximately 30 km north of the Garlock fault near Ridgecrest California. Reports of surface faulting, satellite photo, and high resolution radar (ALOS-2/Sentinal-1 InSAR) images indicate a complex network of faults activated by the sequence. To study the complex relationship between the two large earthquakes we have constructed multi-segment fault models and have carried out a series of geodetic inversions from InSAR and GPS data spanning both events, and kinematic inversions from seismic and GPS data for the two singular events.
We find that the M6.4 event initiates on a NW striking spur of the M7 fault rupture where the immediate foreshocks of the M7 event were located, however the main slip is at shallow depths (<10 km) on the SW striking fault ( ~20 km in length, total moment of 5.3e18 Nm). The stress changes due to the left lateral motion of the main SW striking fault segment of the M6.4 event appear to affect the M7 rupture. The overall rupture of the M7 event is approximately 40 km in length, extending 10 km NW of the hypocenter and 30 km to the southeast with a total scalar moment of 4.6e19 Nm. The main slip is located between 10 km to the NW and 10 km to the SE of the hypocenter. The rupture kinematics reveals a relatively slow average rupture, where the southeastward propagating rupture front seems to be initially delayed at the juncture with the M6.4 SW fault, perhaps due to a relaxation barrier due to slip on the NW striking fault during the M6.4 rupture, and/or the clamping stress applied SE of the juncture on the NW striking plane. However, the barrier was overcome and the rupture extended about 20 km SE. Immediately NW of the juncture is where the greatest slip was achieved possibly from reduction of fault-normal stress in that region due to the M6.4 earthquake. The InSAR data contains information from both earthquakes and it is difficult to isolate the two events. On the other hand, the high spatial resolution of these data provides additional detail about slip on secondary fault strands and the complex rupture geometry. We will report on a series of independent seismic waveform and GPS inversions to compute InSAR residuals to construct self-consistent finite-source inversions using the joint seismic waveform, GPS and InSAR data sets.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S31G0494D
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY