Shaking‐Induced Small Seismic Velocity Changes as Revealed From Seismic Interferometry Analysis of Distributed Acoustic Sensing Data

Abstract Understanding the spatio‐temporal variations in the physical properties of the Earth's crust is crucial for comprehending the dynamic processes linked to earthquakes. Conventional seismometer‐based analyses have limitations in spatio‐temporal resolution due to the sparse station distribution. Using seismic interferometry with distributed acoustic sensing (DAS), we mapped coseismic velocity changes associated with a M4.1 earthquake 40 km away from Sakurajima volcano, Japan, with high spatial resolution. We observed velocity decreases of up to 1.0% in the 2–3 Hz band in sedimentary or old lava regions with low S‐wave velocity, demonstrating enhanced sensitivity of unconsolidated materials to seismic perturbation. By stacking seismic ambient noise cross‐correlation functions (CCFs) from many channel pairs, we improved the signal‐to‐noise ratio sufficiently to estimate relative velocity changes with a temporal resolution of 30 min. Although peak ground velocities observed at seismic stations are one‐tenth (0.16 cm/s) of previous studies, we observed comparable seismic velocity reductions and recovery rates until approximately 12 hr after the earthquake. Since DAS can provide dense measurements along fiber‐optic cables, it offers new opportunities to investigate seismic velocity changes with high spatial detail and, through stacking seismic ambient noise CCFs from many channel pairs, improved temporal resolution.