Imaging the rupture process of the 2019 M6.4 and M7.1 Ridgecrest Earthquakes using local seismic stations in Southern California

Yuqing Xie, & Lingsen Meng

Published August 14, 2019, SCEC Contribution #9674, 2019 SCEC Annual Meeting Poster #258

The M6.4 and M7.1 Ridgecrest earthquakes shocked downtown LA in July 2019. The earthquakes draw many attentions since they are among the largest earthquakes in Southern California over the past two decades. They are recorded by the dense strong motion stations and broadband seismic stations in Southern California. In this study a multi-array back-projection method using local seismic networks (epicentral distance between 1.5 and 2.5 degrees) are used to image the M7.1 and M6.4 earthquakes. The local BPs (back-azimuth) using individual arrays are first calculated, and then merged into a single image of the rupture process. Preliminary results show that both earthquakes rupture along the surface fault traces. The M6.4 foreshock starts from the junction of the conjugate fault system and ruptures along a SW-NE-strike branch for about 10 km. The M7.1 event ruptures along the NW-SE-strike fault for about 15 km. Both of the two earthquakes have relative slow rupture velocity close to 1.5 km/s. Various degrees of back-azimuth errors are observed for different arrays, which are possibly caused by lateral heterogeneity of the seismic velocity, coda waves and multi-phases. The relatively simple rupture processes of a strike-slip fault earthquake provide an opportunity to validate the local back-projection method and to further improve it by optimizing better array configuration. Future work includes understanding and reducing the slowness direction deviations due to local 3D structures. We are also interested in demonstrating the potential for rapid source characterization, since the local BP method measures the rupture length and rupture velocity with a relatively short time frame.

Key Words
Ridgecrest earthquake, Back projection, Southern California network

Citation
Xie, Y., & Meng, L. (2019, 08). Imaging the rupture process of the 2019 M6.4 and M7.1 Ridgecrest Earthquakes using local seismic stations in Southern California. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes