2025-12-12 九州大学
図1 本研究でDAS観測を行なっている領域（緑色の線がDAS観測に使用したケーブルを示す。四角形は、海底地震観測網DONETの観測点の位置を示す。灰色・赤色の丸や星印は、先行研究（Takemura et al., 2022; Tamaribuchi et al., 2022; Baba et al., 2023）のスロー地震の震源を示す。）
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/researches/view/1379
- https://www.kyushu-u.ac.jp/f/64186/25_1212_01.pdf
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL118973
能登半島地震（マグニチュード7.6）後、南海トラフ付近の浅い微動が活発化 Shallow Tremors Near the Nankai Trough Activated After the M 7.6 Noto Peninsula Earthquake
Satoru Baba, Eiichiro Araki, Takane Hori
Geophysical Research Letters Published: 25 November 2025
DOI:https://doi.org/10.1029/2025GL118973
Abstract
Off the Cape Muroto near the Nankai Trough, small shallow tremor activity was observed by distributed acoustic sensing (DAS) and offshore seismic network DONET after the 2024 M7.6 Noto Peninsula earthquake approximately 600 km away. After the mainshock, DAS continued observation including tremors more stably than DONET; therefore, DAS can be an effective means in monitoring seismicity when a large earthquake occurs. We located these tremors on the western edge of the slow earthquake area by envelope correlation and amplitude attenuation property with distance. These tremors activated several hours after the passage of surface waves of the earthquake. The number of tremors was larger than background tremor activity rate; therefore, this tremor activity can be related to the Noto Peninsula earthquake. A transient loading by the Noto Peninsula earthquake may have advanced the tremor occurrence, or pore pressure redistribution by a stress change may have caused the tremors.
Plain Language Summary
Slow earthquakes are phenomena with longer characteristic durations than regular earthquakes. After the M7.6 Noto Peninsula earthquake which occurred on 1 January 2024, small tremor activity, a type of slow earthquakes, has been observed off the Cape Muroto along the Nankai Trough, approximately 600 km apart from the epicenter. This activity was observed by an offshore seismic network DONET and distributed acoustic sensing (DAS) measurement, which utilizes a fiber-optic cable as a strain rate sensor array. We located these tremors on the western edge of the slow earthquake area suggested in previous studies. Generally, more than 10 tremors do not occur per day by background tremor activity only; therefore, this tremor activity is considered to be related to the Noto Peninsula earthquake. A transient loading by the Noto Peninsula earthquake may have caused the tremor activity.
Key Points
- We observed a shallow tremor activity by DONET2 and DAS off the Cape Muroto a few hours after the 2024 Mj 7.6 Noto Peninsula earthquake
- These tremors were located at the western edge of the slow earthquake area clarified by previous studies
- A transient stress change by the Noto Peninsula earthquake may have caused the delayed triggering of the tremor activity
