10:00 AM - 10:15 AM
[SCG44-16] Probe into Slow & Fast Earthquakes by Distributed Acoustic Sensing (DAS)
Keywords:DAS, Slow earthquakes
Distributed Acoustic Sensing (DAS) can detect seismic vibrations every few meters of a long optical fiber cable for tens of kilometers, by emitting Laser light into the cable and processing the light scattered back to the source (e.g., Zhan et al., 2019). DAS system have been used to probe into seismic wavefield from local to regional earthquakes at various tectonic environments around the globe (e.g., Lindsey et al., 2017; Jousset et al., 2018; Wang et al., 2018; Nishimura et al., 2021; Shinohara et al., 2021).
We have performed the seismic observations combining a DAS system (ONYX Mk1.0) developed by Sintela Ltd with telecommunication optical fiber cables in the Central Shikoku, SW Japan. The dynamic strain signals along the optical fiber cable have been continuously recorded with a sampling frequency of 500 Hz, a spatial interval of ~5.0 m, and a gauge length of ~10 m for more than approximately three months.
We succeeded to detect wavefronts radiated from a few low-frequency earthquakes (LFEs) at the down-dip extension of the strongly locked area along the Nankai subduction zone. The wave arrivals well match with those observed by a nearby permanent seismic station. However, the signal amplitude of the LFEs is relatively weak compared with traffic and DAS-self noises, resulting to difficulty of continuous tracking of the move-out along the fiber cable. Furthermore, heterogeneous coupling of the cable with ground produces apparent variation of signal-to-noise ratio. This is the first report to identify seismic signals linked to LFEs using DAS system.
In addition, we have obtained seismic wavefronts from many small to large fast (regular) earthquakes in and around the Central Shikoku. Using waveforms radiated a nearby event pair consisting of two M~2 earthquakes, we calculated accurate differential travel time applying cross-correlation technique. The differential travel time data along the fiber cable has a strong impact on the constraint on the relative hypocenter location.
We have performed the seismic observations combining a DAS system (ONYX Mk1.0) developed by Sintela Ltd with telecommunication optical fiber cables in the Central Shikoku, SW Japan. The dynamic strain signals along the optical fiber cable have been continuously recorded with a sampling frequency of 500 Hz, a spatial interval of ~5.0 m, and a gauge length of ~10 m for more than approximately three months.
We succeeded to detect wavefronts radiated from a few low-frequency earthquakes (LFEs) at the down-dip extension of the strongly locked area along the Nankai subduction zone. The wave arrivals well match with those observed by a nearby permanent seismic station. However, the signal amplitude of the LFEs is relatively weak compared with traffic and DAS-self noises, resulting to difficulty of continuous tracking of the move-out along the fiber cable. Furthermore, heterogeneous coupling of the cable with ground produces apparent variation of signal-to-noise ratio. This is the first report to identify seismic signals linked to LFEs using DAS system.
In addition, we have obtained seismic wavefronts from many small to large fast (regular) earthquakes in and around the Central Shikoku. Using waveforms radiated a nearby event pair consisting of two M~2 earthquakes, we calculated accurate differential travel time applying cross-correlation technique. The differential travel time data along the fiber cable has a strong impact on the constraint on the relative hypocenter location.