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Ambient noise monitoring of stress-induced seismic velocity changes associated with the 2019 Ridgecrest earthquake sequence

Yanru An, & Taka'aki Taira

Published August 12, 2021, SCEC Contribution #11286, 2021 SCEC Annual Meeting Poster #194

An improved understanding of the stress field in the seismogenic crust is central to studies of earthquake physics and its spatial variations will provide crucial observational insights into the faulting processes. The 2019 Ridgecrest earthquake sequence has generated notable surface rupture and produced significant pgv near the rupture area and the Coso Geothermal Field (CGF). In order to study spatio-temporal evolutions of the state of stress at seismogenic depth, we examined temporal characteristics of Green’s functions through cross-correlation analysis of seismic ambient noise, evaluating seismic velocity changes (dv/v) to quantify the co-seismic velocity changes and subsequent the healing processes.

Three years of continuous seismic data (2018 to 2020) from 22 seismic stations were analyzed. The majority of stations are located within 50 km from the sequence. Our analysis focused on using vertical component data in a frequency band of 0.1-0.9 Hz. We obtained time histories of dv/v for 231 pairs of two seismic stations. A nonlinear least-square inversion involving a bootstrap approach was applied to dv/v time-series data to characterize the temporal behavior of the observed co-seismic velocity changes and post-seismic recovery and also to estimate the static and the dynamic dv/v changes at each station.

We observed a sudden dv/v reduction immediately after the M7.1 Ridgecrest mainshock and the largest co-seismic velocity change exceeds -0.5% near the rupture area and -0.25 % at the CGF, and then the dv/v gradually increased. The characteristic recovery time is found to range from about 40 days to ~10 years for our target area.

Based on the ratio of peak ground velocity from the M6.4 and M7.1 events, we calculated the dynamic co-seismic dv/v changes due to the two earthquakes. Results suggest that except the station LRL located at the end of the M6.4 event rupture, dynamic dv/v of stations induced by the M7.1 event are larger than that of the M6.4 event.

An, Y., & Taira, T. (2021, 08). Ambient noise monitoring of stress-induced seismic velocity changes associated with the 2019 Ridgecrest earthquake sequence. Poster Presentation at 2021 SCEC Annual Meeting.

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