[S-TT36] Applying optic fiber sensing to earth science

[STT36-P10] Technical reports on distributed acoustic sensing measurements of the Noto Peninsula earthquake swarm in 2023

*Masatoshi Miyazawa¹, Eiichiro Araki², Yoshiyuki Tanaka³ (1.Kyoto University, 2.JAMSTEC, 3.Univ. of Tokyo)

Keywords:DAS, Noto Peninsula earthquake swarm

Distributed acoustic sensing (DAS) measurements were conducted for about four months in total in 2023 at the Noto Peninsula in central Japan. This region has experienced an increasing number of earthquakes in the crust since the end of 2020. The measurements were taken using a commercial optic fiber cable that was about 27 km long and installed in the southern to southwestern part of the region adjacent to the earthquake swarm activity area. The DAS technique allowed us to acquire many seismic records from earthquakes, similar to the previous studies that measured the seismic wavefields using optic fiber cables installed beneath the ground. Additionally, we were able to prove that the seismic phases can be identified in the overhead wire sections between poles as well. This means optic fiber cables are applicable for earthquake measurements regardless of their placement. We also tested avoiding cycle skipping phenomena by giving a high-frequency time sampling and short gauge length. An M3.2 earthquakes were observed without clipping the amplitude at most channels, and the attenuation characteristics with distance were successfully shown. Furthermore, seismic records with a high signal-to-noise ratio showed the seismic phases that likely indicate the reflected S-waves in the deeper part of the seismicity. In summary, our observations demonstrated the high potential of the DAS technique using optic fiber cables to investigate the seismicity and the seismic structure regardless of whether the cable section is under the ground or overhead.