Assessing the Earthquake Recording Capability of an Ocean-bottom Distributed Acoustic Sensing Array in the Sanriku region, Japan

Sparse seismic instrumentation in the oceans limits our understanding of the Earth’s dynamics. The emerging technology of Distributed Acoustic Sensing (DAS), which can turn existing fiber-optic cable arrays into thousands of seismic sensors, has the potential to fill the data gap. Yet, the power of OBDAS for routine seismic monitoring has to be further explored. In this study, we investigate the recording capability of an ocean-bottom DAS (OBDAS) array in the Sanriku region, Japan. We first compare the manually selected OBDAS recordings with a collocated Ocean-Bottom Seismometer (OBS) and demonstrate that OBDAS could record high-fidelity earthquake waveforms when earthquake amplitude power exceeds the OBDAS noise floor. We then propose two array-based detection methods, Waveform Similarity Search and Spectrum Similarity Search workflows, to detect coherent signals across the OBDAS array. With such workflows, we successfully detect ~ 80% of cataloged earthquakes within a 100 km radius region, as well as thousands of previously uncataloged local events. At the same time, we also show that the quality and quality of recorded waveforms vary substantially across channels. Our results foreshadow an enticing potential of OBDAS to complement the current sparse underwater seismic network for observational seismology studies.