Fault Zone Imaging with Distributed Acoustic Sensing: Surface-to-Surface
Fault zone complexities contain important information about earthquake
physics. 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
spurious arrivals and coda waves 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
USGS Quaternary Fault database of the United States but are more
precise. 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.