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We present a novel type of multicomponent sensor prototype that uses distributed acoustic sensing (DAS) technology. A prototype of the new sensor has three individual parts consisting of optical fiber wound around a polyvinyl chloride frame. We deployed the sensor prototype at a test site and recorded seismic waves generated by a wooden hammer. A geophone array was also set for comparison purposes. The data observed with the new DAS sensor prototype show good agreement with the conventional geophone. The particle motion of waveforms obtained by the DAS sensor prototype shows ellipsoidal motion, the propagating velocity of which coincides with the velocity of the Rayleigh waves estimated by the dispersion curve based on the geophone data. We introduced a simple string model to explain the dynamic behavior of the sensor. The analysis results of the string model can explain features of recorded seismic data. These results indicate that the DAS sensor prototype records seismic waves via lateral vibration of the string. The present study shows a new possibility of the multicomponent sensor with the DAS technology.

Data acquired by eight seafloor observatories installed in Japanese waters have revealed a number of qualities which are important for disaster mitigation. These qualities include: detailed microearthquake activities before and after a plate boundary earthquake, the existence of microtsunamis, the advantages in early detection of tsunamis, the importance of seafloor geodetic observations, etc. These new advancements were brought by passive, real-time, and continuous time series of earthquake and tsunami records on the seafloor. Knowledge about earthquake source mechanisms has revealed the possibility of the detection of spatiotemporal changes in physical properties of interplate boundaries in terms of seismic asperities. We propose that the detection of such physical property changes becomes possible when we combine seafloor observations and active seismic sources dedicated to precise monitoring of reflection amplitudes at plate boundary interfaces. After the 2011 earthquake off the Pacific coast of Tohoku, three earthquake monitoring cabled observatories were deployed to improve the resilience to future earthquake and tsunami hazards. We believe that the development of active monitoring/mapping technologies must be seriously considered to exert maximum utilization of an offshore earthquake monitoring system.