High-resolution fault imaging along DAS cable using spurious arrivals in noise interferometry

Ambient noise interferometry has been applied to traditional sensors for decades to image crustal and upper-mantle structure. Recently, the emerging Distributed Acoustic Sensing (DAS) technique has enabled imaging the near-surface structure in urban areas by utilizing existing telecommunications infrastructure and anthropogenic sources. With dense sensors in several meters spacing, the unaliased wavefield can provide unprecedented details. The spurious arrivals preceding the inter-station surface waves produced by strong scatter energy can be used to map the passive scatterers such as faults. In this work, we convert a 10-km underground fiber-optic cable across the Ridgecrest City to a DAS array and cross-correlate three months traffic noise. Both inter-station direct waves and spurious precursors are clearly observed. We use the direct waves to build a 2D group velocity model and map the spurious arrivals to several strong scatterers. The three faults across the array in USGS database were all detected. We also resolve a strong but previously unmapped fault. The mapped faults produce scatter energy with distinct frequency dependency, which may be indicative of the fault zone properties.