Imaging the Japan Trench Subduction Zone Subsurface with an Ocean-Bottom Fiber-Optic Cable

Abstract:

Distributed acoustic sensing (DAS) recently became a powerful tool in seismology by transforming telecommunication fiber-optic cables into arrays of thousands of sensors. In this study, we focus on an offshore cable deployed in the Sanriku region, Japan, near the 2011 M_w 9.0 Tohoku-Oki earthquake rupture area. In November 2019, a DAS interrogator was connected to the cable for two weeks converting the first 100 km of the cable from the coast towards the trench into an array of approximately 19,000 seismic sensors. We first take advantage of deep learning algorithms to detect regional and teleseismic earthquakes and to pick their P- and S-wave arrival times. We show that the seismic wave arrival times can be used to image the subduction zone. We also compute the autocorrelations of S-waves from regional earthquakes recorded along the cable to retrieve the S-wave reflectivity response of the medium. This study demonstrates that ocean-bottom DAS can be used to gain new insights into the velocity structure of subduction zones.