Abstract
AbstractThe spatial variation of azimuthal S‐wave phase velocity anisotropies caused by differential horizontal stress along the Nankai Trough was analyzed to understand the stress state of the overhung block of the forearc region, off Kii Peninsula, Japan. We conducted controlled‐source seismic surveys along the circumference of a 3 km radius circle centered at each seismometer of a cabled seafloor observatory installed in the Nankai subduction zone. We applied an anisotropy semblance method to estimate the orientation of fast and slow S‐wave velocities of shallow sediments and deep accretionary prism using the multi‐azimuth seismic dataset acquired at each seismometer location. The estimated orientations of fast S‐wave velocity are parallel to the convergent direction of the subducting place beneath the Kumano basin in the deeper accretionary prism while perpendicular to the convergent direction in the shallow sediments inside the Kumano basin. These fast S‐wave polarization orientations in shallow sediments show good agreement with horizontal maximum stress orientations estimated in situ borehole measurements in the observation area. We estimated the differential horizontal stress field in the Nankai Trough region from obtained S‐wave anisotropy using a simple crack model. Using this method, we first suggest the convergent‐parallel horizontal maximum compression in the deeper part of the accretionary prism above the locked portion. Assuming obtained S‐wave anisotropy is attributed to the tectonic loading by the subducting plate, these results suggest that the S‐wave azimuthal anisotropy measurements can be used to monitor the subsurface stress field as a function of time.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call