Simultaneous seafloor seismic observation by distributed acoustic sensing and accelerometer using off-Sanriku optical cable observation system

Recently Distributed Acoustic Sensing (DAS) measurement becomes popular for seismic observation due to its spatially high-density. We have conducted nine DAS measurements using a spare fiber of the optical seafloor cable seismic tsunami observation system off Sanriku, northeastern Japan from February 2019, and evaluated performance of the DAS data. For each observation, many earthquakes were observed and we compared DAS records to records from the cabled seismometer. It is found that system noise level of DAS measurement is the same as that of the seismometer. Seismic survey using controlled sources and DAS measurement on the seafloor cable was carried out in November 2020, and the signals from the controlled sources were clearly recorded. Clear reflection images were obtained using DAS data by elementary seismic data processing. In addition, a linearity of amplitude response was confirmed under the condition of small amplitude. DAS measurement can be quantitatively applied in an observation of earthquakes on the seafloor.