Fault Zone Imaging With Distributed Acoustic Sensing: Surface-To-Surface Wave Scattering

Abstract

Fault zone complexities contain important information about factors controlling earthquake dynamic rupture. High-resolution fault zone imaging requires high-quality data from dense arrays and new seismic imaging techniques that can utilize large portions of recorded waveforms. Recently, the emerging Distributed Acoustic Sensing (DAS) technique has enabled near-surface imaging by utilizing existing telecommunication infrastructure and anthropogenic noise sources. With dense sensors at several meters' spacing, the unaliased wavefield can provide unprecedented details for fault zones. In this work, we use a DAS array converted from a 10-km underground fiber-optic cable across Ridgecrest City, California. We report clear acausal and coda signals in ambient noise cross-correlations caused by surface-to-surface wave scattering. We use these scattering-related waves to locate and characterize potential faults. The mapped fault locations are generally consistent with those in the United States Geological Survey Quaternary Fault database of the United States but are more accurate than the extrapolated ones. We also use waveform modeling to infer that a 35 m wide, 90 m deep fault with 30% velocity reduction can best fit the observed scattered coda waves for one of the identified fault zones. These findings demonstrate the potential of DAS for passive imaging of fine-scale faults in an urban environment.

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