Toward Back-Projection Earthquake Rupture Imaging With Ocean Bottom Distributed Acoustic Sensing

Abstract

Distributed acoustic sensing (DAS) along seafloor fiber optic cables offers high-density, wide-aperture, real-time seismic data near subduction earthquakes, at a lower cost than conventional cabled ocean bottom seismic networks. It is thus a very promising approach to develop offshore observatories for hazard monitoring and mitigation and for fundamental research on earthquake processes. Here, we introduce a method for earthquake rupture imaging by back-projection of DAS data, taking full advantage of the data characteristics to achieve high resolution and accuracy. To develop and test the method, we use DAS data recorded along submarine telecom cables in Chile. The approach includes pre-processing steps, such as spatial integration and sediment time corrections, that greatly improve the back-projection performance. Our analysis of recordings of small earthquakes that can be considered as point sources demonstrates high accuracy in localizing seismic sources, with a resolution ranging from 2 to 5 km within a “high-resolution and high-robustness zone” around the cable. We demonstrate the ability of the method to image large ruptures by applying it to simulated waveforms of a magnitude seven earthquake, constructed by superposition of multiple empirical Green's functions. We find that strong coda waves do not compromise the precise detection and location of sub-sources. Our method could enhance early warning systems and offer high-resolution observations crucial for studying fault mechanics.