To investigate the mechanism of tectonic tremor and the factors that influence its occurrence and fluctuations, we use seismic reflection data to map in detail a shear zone associated with the plate boundary fault in the Nankai accretionary prism, southwest Japan. The shear zone can be identified from its low seismic velocity and low reflection amplitude, which may signify the presence of high pore pressure, around the transition boundary from frontal outer wedge to inner wedge. A detailed comparison of the mapped shear zone and the distribution of tectonic tremor demonstrate that tremor tended to occur in the thick part of the shear zone, where high pore fluid pressure may weaken faults and thereby facilitate slow earthquakes. Furthermore tremors align on the oblique strike-slip faults that caused variation of the shear zone thickness as well as fluctuation of stress and pore pressure. The oblique strike-slip faults that control the thickness of the shear zone and tremor distributions are interpreted as features formed by the collision of an accretionary prism against a landward tectonic backstop.
All Science Journal Classification (ASJC) codes
- Earth-Surface Processes