3:30 PM - 3:45 PM
[STT42-07] Illuminating a Small Earthquake Cluster with DAS Arrays in Central Shikoku, Japan
Keywords:DAS, hypocenter determination
Precise hypocenter determination is fundamentally important in understanding the space-time evolution of earthquakes, including fault geometry. Achieving higher accuracy requires travel-time data from dense seismic station networks. Distributed Acoustic Sensing (DAS) technique provides high spatial density measurements, enabling precise determination of hypocenter. In this study, we apply the hypoDD algorithm (Waldhauser & Ellsworth, 2000) to travel-time data recorded by DAS arrays in Central Shikoku, Japan, to determine the hypocenters of a small earthquake cluster.
We conducted DAS measurements from mid-January to the end of March 2024 using two independent fiber-optical cables along national roads in Central Shikoku. The total acquisition length was 50.7 km and 63.8km, respectively, with a gauge length of 13.47 m, a channel pitch of 4.96 m, and a sampling frequency of 200 Hz. We analyzed a total of ten earthquakes that occurred close to one of the cables, five of which were earthquakes listed in the JMA unified earthquake catalog and the remaining five were microearthquakes detected by template matching using continuous waveform data recorded by the nation-wide seismic network. We visually identified the arrival times of P- and S-waves and calculated the travel-time differences for each event pair at each station. To obtain more precise differential data, we cross-correlated waveforms around the arrival times. The relocated hypocenters exhibit a planar alignment, suggesting the presence of a previously unrecognized small fault in the crust. This alignment strikes roughly north-south, perpendicular to the Median Tectonic Line. Additionally, we estimated the focal mechanism of one event using the nationwide seismic network, providing insights into the geometry of the unrecognized fault. DAS has a great potential to reveal fault geometry of small earthquake cluster.
We conducted DAS measurements from mid-January to the end of March 2024 using two independent fiber-optical cables along national roads in Central Shikoku. The total acquisition length was 50.7 km and 63.8km, respectively, with a gauge length of 13.47 m, a channel pitch of 4.96 m, and a sampling frequency of 200 Hz. We analyzed a total of ten earthquakes that occurred close to one of the cables, five of which were earthquakes listed in the JMA unified earthquake catalog and the remaining five were microearthquakes detected by template matching using continuous waveform data recorded by the nation-wide seismic network. We visually identified the arrival times of P- and S-waves and calculated the travel-time differences for each event pair at each station. To obtain more precise differential data, we cross-correlated waveforms around the arrival times. The relocated hypocenters exhibit a planar alignment, suggesting the presence of a previously unrecognized small fault in the crust. This alignment strikes roughly north-south, perpendicular to the Median Tectonic Line. Additionally, we estimated the focal mechanism of one event using the nationwide seismic network, providing insights into the geometry of the unrecognized fault. DAS has a great potential to reveal fault geometry of small earthquake cluster.