The Potential of DAS in Seismic Hazard Analysis: A Case Study of Ridgecrest City DAS Array

Yan Yang, Ethan F. Williams, Jack B. Muir, & Zhongwen Zhan

Published August 13, 2020, SCEC Contribution #10499, 2020 SCEC Annual Meeting Poster #210

Shallow shear-velocity structure is closely related to earthquake ground motion intensity. However, the shallow structure often has vertical and lateral heterogeneities over very small distances that can only be resolved by high-resolution, high-frequency seismic experiments, which complicates the prediction of earthquake ground motion amplification. Distributed acoustic sensing (DAS) can turn existing fiber-optic cables into low-cost dense seismic arrays and is capable of resolving shear velocity in the top tens of meters. After the Ridgecrest M7.1 earthquake in early July 2019, we deployed four DAS arrays in the epicentral and surrounding regions. We apply ambient noise tomography to the 10-km linear DAS array in the city of Ridgecrest and get a high-resolution 2-D shear-velocity profile of the top 100 meters. The profile reveals notable lateral variation of shear velocity by 25%, even though the entire array is within the basin. The DAS array also recorded thousands of aftershocks during its operational time. We extract site response from the aftershock ground motions. The Vs30 computed from our velocity model shows very good correlation with the site response in 1-10 Hz frequency band. These results demonstrate the value of DAS for seismic hazard analysis at very fine scales and establish a framework for high-resolution seismic site characterization which we will apply throughout Southern California.

Citation
Yang, Y., Williams, E. F., Muir, J. B., & Zhan, Z. (2020, 08). The Potential of DAS in Seismic Hazard Analysis: A Case Study of Ridgecrest City DAS Array. Poster Presentation at 2020 SCEC Annual Meeting.

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