Sub‐Kilometer Correlation Between Near‐Surface Structure and Ground Motion Measured With Distributed Acoustic Sensing

Abstract

Earthquake ground motion depends strongly on near-surface structure, which is challenging to image in urban areas at high resolution. Distributed acoustic sensing (DAS) is an emerging technique that provides a scalable solution by converting preexisting fiber-optic cables into dense seismic arrays. After the July 2019 M7.1 Ridgecrest earthquake, we converted an underground dark fiber across the city of Ridgecrest, CA, into a DAS array. The recorded aftershocks show substantial lateral variability in site amplification over only 8-km in distance. To understand the cause of such variability, we used three months of continuous data, dominated by traffic-generated seismic noise, to image near-surface structure along the fiber path. We find that the lateral variations of earthquake shaking correlate well with the shallow shear velocity model at sub-kilometer scales, in particular micro-basins filled with soft sediments. These results highlight the great potential of DAS for high-resolution seismic hazard mapping in urban areas.