Strong Ground Motions from 2019 Ridgecrest Earthquake Sequence Mainshocks

Silvia Mazzoni, Tadahiro Kashida, Pengfei Wang, Sean K. Ahdi, Yousef Bozorgnia, & Jonathan P. Stewart

Submitted August 15, 2019, SCEC Contribution #9774, 2019 SCEC Annual Meeting Poster #248 (PDF)

Poster Image: 
The Ridgecrest Earthquake sequence included a M6.4 foreshock on 4 July 2019 and a M7.1 mainshock event on 5 July 2019. These events occurred in the Eastern California Shear Zone, near Indian Wells Valley, south of China Lake and west of Searles Valley. The M6.4 and M7.1 events were recorded by approximately 500 and 800 ground motion stations, respectively, belonging to nine different seismographic networks. Preliminary source, path, and site metadata were compiled for all stations and recordings. 1232 ground motions recordings were processed using standard procedures defined by the PEER Center for the NGA projects. Computed intensity measures include peak ground acceleration (PGA) and pseudo-spectral acceleration response spectra (PSA) at 111 oscillator periods. Preliminary analyses and comparisons to existing NGA-West2 models do not show appreciable overall bias (indicating adequate performance of source terms) and consistent attenuation of amplitudes with distance, which indicates that the California-specific path model is effective. Preliminary analysis of data show that ground motions were amplified for softer site conditions at longer periods, consistent with typical patterns in California. Apparent directivity effects observed include fault-normal ground motions controlling the maximum component at stations off the end of the M7.1 fault, whereas stations near the epicenter have no such polarization and generally weaker long-period ground motions.

Key Words
2019 Ridgecrest Ground Motions

Citation
Mazzoni, S., Kashida, T., Wang, P., Ahdi, S. K., Bozorgnia, Y., & Stewart, J. P. (2019, 08). Strong Ground Motions from 2019 Ridgecrest Earthquake Sequence Mainshocks. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Ridgecrest Earthquakes