12:00 〜 12:15
[SSS03-12] Shear velocity tomography using seismic noise interferometry from a linear OBS array off Kumano crossing Nankai Trough
キーワード：shear velocity tomography in marine subduction zone, ambient noise differential adjoint tomography, Nankai Trough and low-velocity zone
Shear velocity structure combined with P velocity model from exploration surveys is useful information for marine sediment characterization, strong seafloor motion prediction and accurate hypocenter determination. Particularly in the Nankai Trough, it is an urgent issue for disaster prevention. It is also sensitive to micro cracks filled with water, and hence capable of understanding hydrological processes in the accretionary prism. However, only a few results related to shear wave velocity structure based on offshore wide-angle seismic surveys around the Nankai Trough are available so far (e.g., Takahashi et al., 2002), because the direct S-wave cannot be generated by controlled source in the seawater.
In this study, we perform seismic noise interferometry to derive the shear velocity model beneath a linear OBS array of 30 stations that started from off-shore Kumano and extended across Nankai Trough obtained in 2009. The passive noise recording length is more than 50 days and we rotate the horizontal components to radial and transverse directions based on the active-source survey data along the same array, with stacking the cross correlation over the entire observation period. We extract Love wave dispersion from noise cross correlations between periods 3.5-8 s. The initial phase velocity image reveals a 15-km-wide low-velocity zone (period 5.3-8 s; velocity 0.8-1.2 km/s) beneath the Kumano basin. The low-velocity zone is located at ~75 km south of the coast and ~35 km north from the Nankai trench axis. We also identify a low-velocity structure ~10 km south of the trench axis, which coincides with the Zenisu ridge/seamount. We will convert the phase velocity to shear velocity versus depth based on the standard 1D layered depth inversion for each horizontal grid location. Additionally, we will perform ambient noise differential adjoint tomography (e.g. Liu 2020, JGR; Liu & Beroza 2021, JpGU) to improve the shear velocity model. The updated results will be presented at the meeting.
This study is part of 'Research Project for Disaster Prevention on the great Earthquakes along the Nankai Trough' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan.
In this study, we perform seismic noise interferometry to derive the shear velocity model beneath a linear OBS array of 30 stations that started from off-shore Kumano and extended across Nankai Trough obtained in 2009. The passive noise recording length is more than 50 days and we rotate the horizontal components to radial and transverse directions based on the active-source survey data along the same array, with stacking the cross correlation over the entire observation period. We extract Love wave dispersion from noise cross correlations between periods 3.5-8 s. The initial phase velocity image reveals a 15-km-wide low-velocity zone (period 5.3-8 s; velocity 0.8-1.2 km/s) beneath the Kumano basin. The low-velocity zone is located at ~75 km south of the coast and ~35 km north from the Nankai trench axis. We also identify a low-velocity structure ~10 km south of the trench axis, which coincides with the Zenisu ridge/seamount. We will convert the phase velocity to shear velocity versus depth based on the standard 1D layered depth inversion for each horizontal grid location. Additionally, we will perform ambient noise differential adjoint tomography (e.g. Liu 2020, JGR; Liu & Beroza 2021, JpGU) to improve the shear velocity model. The updated results will be presented at the meeting.
This study is part of 'Research Project for Disaster Prevention on the great Earthquakes along the Nankai Trough' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan.