Observation of Shallow Slow Earthquakes by Distributed Acoustic Sensing Using Offshore Fiber‐Optic Cable in the Nankai Trough, Southwest Japan

Off Cape Muroto area, along the Nankai Trough in southwest Japan, is a typical area with adjacent occurrences of slow and megathrust earthquakes. High-resolution monitoring earthquakes necessary to understand tectonic conditions. In off distributed acoustic sensing (DAS) measurement, which provides high-density strain data, has been conducted using offshore fiber-optic cable. We observed shallow tremors, type earthquakes, DAS measurement for first time. The characteristics tremor signals recorded by were longer durations than those seismographs composed several phases apparent velocities hundreds m/s km/s that are coherent only tens meters. By combining seismograph we located these tremors around subducted seamount peak. Therefore, spatial relationship between structural suggested. This pioneering study earthquake observation DAS.