Seismic Velocity Changes Associated with the 2019 Ridgecrest Earthquake Sequence

Yanru An, Taka'aki Taira, Chenyu Li, & Zhigang Peng

Submitted August 15, 2019, SCEC Contribution #9765, 2019 SCEC Annual Meeting Poster #261

The 2019 M 7.1 Ridgecrest earthquake sequence triggered widespread local and regional seismicity including the Coso Geothermal Field (CGF). To understand spatiotemporal variations in stress transients associated with the Ridgecrest sequence, we search for stress-induced seismic velocity changes around the rupture area of the M 7.1 Ridgecrest earthquake and the CGF by using ambient noise seismic interferometry. We analyzed over 7 months of continuous recordings (January through early August 2019) from 22 seismic stations. The majority of stations are located within 50 km from the sequence. Our analysis involves cross-correlating seismic data from all possible pairs of two stations in 9 frequencies and 9 different combinations of components (RR,RT,RZ,TR,TT,TZ,ZR,ZT, and ZZ), and also uses a moving-window cross-spectrum approach to evaluate seismic velocity change. All pairs of stations with 9 components are combined together to obtain an average velocity change in the study area.

Our analysis finds a sudden velocity decrease (~0.25%) in a frequency range of 0.1 to 0.9 Hz following the M 7.1 Ridgecrest earthquake. This is consistent with other recent observations of velocity reductions following moderate or large earthquakes elsewhere around the world. However signals from abundant aftershocks may introduce bias in our velocity measurements. We will systematically investigate effects from local aftershocks on the velocity measurements and will compare the observed velocity changes with triggered seismicity changes in the CGF. In addition, we plan to examine velocity changes with varying station pairs and different frequency ranges to better constrain the spatial variation and depth extent of seismic velocity changes.

Key Words
Seismic Velocity Changes, Ridgecrest Earthquake Sequence

Citation
An, Y., Taira, T., Li, C., & Peng, Z. (2019, 08). Seismic Velocity Changes Associated with the 2019 Ridgecrest Earthquake Sequence. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Ridgecrest Earthquakes