17:15 〜 18:45
[SCG40-P24] Triggered tremor activity off the Cape Muroto observed by distributed acoustic sensing after the 2024 M7.6 Noto Peninsula earthquake
キーワード：分布型音響センシング、誘発微動、スロー地震、南海トラフ
Distributed acoustic sensing (DAS) measurement can measure the temporal change in strain or strain rate along a fiber-optic cable. The major feature of DAS measurement is spatial high density; therefore, seismic observation studies using DAS measurement have increased recently. We have been conducting a DAS measurement off the Cape Muroto along the Nankai Trough continuously since January 2022. Off the Cape Muroto is a typical area where slow earthquake area and coseismic slip area of historical huge regular earthquakes are adjacent. Baba et al. (2023) observed shallow tremors, a type of slow earthquake observed in 2–10 Hz, by the DAS observation. They located these tremors by using DAS and broadband seismograms of the Dense Oceanfloor Network system for Earthquake and Tsunami (DONET) data. These tremors occurred mainly around 134.7ºE and 32.8ºN, which is northeast of the G-node stations of DONET.
In 2024, 13 tremors off the Cape Muroto were observed by DAS data with a 120-km long fiber-optic cable after the M7.6 Noto Peninsula earthquake which occurred at 16:10:22 on January 1st. Since tremor signals were not observed before the earthquake, these tremors can be triggered by surface waves of the Noto Peninsula earthquake. The signals of these tremors propagated from south to north and were not visible near the land in the northern half part of the DAS cable. This is a different characteristic from tremors observed by DAS in 2022, whose signals were observed in the northern part of the DAS cable. Therefore, these tremors are considered to occur more southward than the 2022 tremors and be activated around the southern end of the DAS cable near the trench axis. These signals were also observed by G-node stations of DONET. In G-node stations, tremor signals arrive earlier in the southern station.
By using DAS and seismograph data at G-node stations of DONET, we located these tremors by envelope correlation method based on Ide (2010). The tremors were mainly located around 134.4ºE–134.5ºE and 32.4ºN, which is just above to the east from the southernmost part of the DAS cable. In the future, we will try to improve the location method of tremors and discuss the physical process of triggered tremors.
In 2024, 13 tremors off the Cape Muroto were observed by DAS data with a 120-km long fiber-optic cable after the M7.6 Noto Peninsula earthquake which occurred at 16:10:22 on January 1st. Since tremor signals were not observed before the earthquake, these tremors can be triggered by surface waves of the Noto Peninsula earthquake. The signals of these tremors propagated from south to north and were not visible near the land in the northern half part of the DAS cable. This is a different characteristic from tremors observed by DAS in 2022, whose signals were observed in the northern part of the DAS cable. Therefore, these tremors are considered to occur more southward than the 2022 tremors and be activated around the southern end of the DAS cable near the trench axis. These signals were also observed by G-node stations of DONET. In G-node stations, tremor signals arrive earlier in the southern station.
By using DAS and seismograph data at G-node stations of DONET, we located these tremors by envelope correlation method based on Ide (2010). The tremors were mainly located around 134.4ºE–134.5ºE and 32.4ºN, which is just above to the east from the southernmost part of the DAS cable. In the future, we will try to improve the location method of tremors and discuss the physical process of triggered tremors.