5:15 PM - 7:15 PM
[SCG61-P01] Seismicity beneath Mutsu Bay, Aomori Prefecture, NE Japan, and shear wave splitting analysis on it
Introduction
In the northern part of Honshu, there are several volcanoes and high seismicity occurs. Also, there are faults with strikes of about N-S onshore (in the Natsudomari Peninsula and Shimokita Peninsula). In November 2024, some M4-5 earthquakes occurred in Mutsu Bay. It is unclear whether this recent swarm seismicity is related to faults or volcanic activity beneath the bay.
In an anisotropic media with the preferred orientation of cracks under the differential stress field or structure controlled by faulting, the shear wave splits into two shear waves: a fast shear wave oriented to maximum horizontal stress orientation (SHmax) or fault strike and deformation axis. This study investigates the shear wave splitting in this area and discusses the stress field (e.g., Maeda et al., 2007), fault distribution, and seismicity.
Data and Method
Data are from the unified earthquake catalog by the Japan Meteorological Agency. The analysis period is from 2020 to 2024. We adopted MFAST (Savage et al., 2010) to measure shear wave splitting in the waveform from local seismicity in the area. To obtain the spatial average of fast shear wave oscillation azimuth (FSOA), we used TESSA (Johnson et al., 2011).
Results and discussion
The dominant azimuth of FSOA in the southern and eastern parts of the bay and its surrounding onshore was N-S or NNW-SSE. This azimuth almost corresponds to the fault and anticline strike in onshore Natsudomari and Shimokita Peninsulas, not the SHmax azimuth of about E-W in the corresponding regions C and S of Maeda et al. (2007). This supports that there are several faults and high deformation (e.g., Abe, Tokuyama, and Sakai, Proceeding of the SEGJ Conference, 2002), and it may be supposed the recent seismicity is related to faults beneath the bay.
In the northern part of Honshu, there are several volcanoes and high seismicity occurs. Also, there are faults with strikes of about N-S onshore (in the Natsudomari Peninsula and Shimokita Peninsula). In November 2024, some M4-5 earthquakes occurred in Mutsu Bay. It is unclear whether this recent swarm seismicity is related to faults or volcanic activity beneath the bay.
In an anisotropic media with the preferred orientation of cracks under the differential stress field or structure controlled by faulting, the shear wave splits into two shear waves: a fast shear wave oriented to maximum horizontal stress orientation (SHmax) or fault strike and deformation axis. This study investigates the shear wave splitting in this area and discusses the stress field (e.g., Maeda et al., 2007), fault distribution, and seismicity.
Data and Method
Data are from the unified earthquake catalog by the Japan Meteorological Agency. The analysis period is from 2020 to 2024. We adopted MFAST (Savage et al., 2010) to measure shear wave splitting in the waveform from local seismicity in the area. To obtain the spatial average of fast shear wave oscillation azimuth (FSOA), we used TESSA (Johnson et al., 2011).
Results and discussion
The dominant azimuth of FSOA in the southern and eastern parts of the bay and its surrounding onshore was N-S or NNW-SSE. This azimuth almost corresponds to the fault and anticline strike in onshore Natsudomari and Shimokita Peninsulas, not the SHmax azimuth of about E-W in the corresponding regions C and S of Maeda et al. (2007). This supports that there are several faults and high deformation (e.g., Abe, Tokuyama, and Sakai, Proceeding of the SEGJ Conference, 2002), and it may be supposed the recent seismicity is related to faults beneath the bay.