2:45 PM - 3:00 PM
[STT42-05] Observation of low frequency earthquakes by distributed acoustic sensing around the Tsugaru Strait
Keywords:Distributed acoustic sensing, Low frequency earthquake, Tsugaru Strait, Envelope correlation method
Around the Tsugaru Strait, there are clusters of low frequency earthquakes (LFEs), which are predominant at lower frequencies than regular earthquakes. These LFEs are detected and located by the Japan Meteorological Agency (JMA) and the Association for the Development of Earthquake Prediction (ADEP). However, due to the lack of offshore observation data, detection of LFEs is strongly dependent on onland data. To improve the detection capability of LFEs, reveal their spatiotemporal activities, and discuss their generation mechanism, it is effective to observe LFE signals near the hypocenters by using offshore data. Distributed acoustic sensing (DAS) measurement can measure strain changes along a fiber-optic cable at meter-scale intervals. Taking advantage of its dense measurement, DAS has been widely used for seismic observations recently. Because existing submarine cables can be utilized, DAS can be used for offshore seismic observations at a lower cost than installing ocean bottom seismometers. In this study, we have conducted DAS measurements using submarine cables near the Tsugaru Strait from October 11, 2022 to February 8, 2023, from June 26, 2023 to October 16, 2023, and from September 11, 2024 to February 17, 2025. We investigate the characteristics of LFE signals observed by DAS and examine the detection and location methods for LFEs using DAS and onland seismograph data.
The number of LFEs around the Tsugaru Straits listed in the JMA catalog is approximately 25 in the 8-month DAS observation periods in 2022 and 2023. The signals of these LFEs were observed by the DAS measurement. LFE signals observed by DAS showed that a distinction of P- and S-wave arrivals is difficult and indicated a smaller power spectral density at higher than 4 Hz compared to regular earthquake signals.
For LFEs listed in the JMA catalog in the period from June to October 2023, we located these events based on the envelope correlation method by Mizuno and Ide (2019) by using DAS strain rate waveforms at intervals of 1 km and 13 onland seismic stations of AS-net by ADEP. For most of the LFEs in the southeastern Tsugaru Strait, the epicenter was located with a difference of 2–3 km from that of JMA. On the other hand, for the LFEs near the northeastern coastline of the Tsugaru Strait, the difference in the epicenters between this study and the JMA catalog was more than 10 km. In future works, we will examine the method to improve the accuracy of LFE hypocenters, detect LFEs comprehensively based on the envelope correlation method, and investigate the method to distinguish between LFEs and regular earthquakes automatically.
Acknowledgements: We used seismograph data from AS-net and the earthquake catalog by the Association for the Development of Earthquake Prediction (ADEP). We also used the earthquake catalog by the Japan Meteorological Agency (JMA).
The number of LFEs around the Tsugaru Straits listed in the JMA catalog is approximately 25 in the 8-month DAS observation periods in 2022 and 2023. The signals of these LFEs were observed by the DAS measurement. LFE signals observed by DAS showed that a distinction of P- and S-wave arrivals is difficult and indicated a smaller power spectral density at higher than 4 Hz compared to regular earthquake signals.
For LFEs listed in the JMA catalog in the period from June to October 2023, we located these events based on the envelope correlation method by Mizuno and Ide (2019) by using DAS strain rate waveforms at intervals of 1 km and 13 onland seismic stations of AS-net by ADEP. For most of the LFEs in the southeastern Tsugaru Strait, the epicenter was located with a difference of 2–3 km from that of JMA. On the other hand, for the LFEs near the northeastern coastline of the Tsugaru Strait, the difference in the epicenters between this study and the JMA catalog was more than 10 km. In future works, we will examine the method to improve the accuracy of LFE hypocenters, detect LFEs comprehensively based on the envelope correlation method, and investigate the method to distinguish between LFEs and regular earthquakes automatically.
Acknowledgements: We used seismograph data from AS-net and the earthquake catalog by the Association for the Development of Earthquake Prediction (ADEP). We also used the earthquake catalog by the Japan Meteorological Agency (JMA).