[SCG52-P04] The genesis of seismic clusters in the subducting oceanic crust
Keywords:intraslab earthquake, volume reduction
First, we relocated upper-plane earthquakes by double-difference hypocenter location method (hereinafter called “DD method”) [Waldhauser and Ellsworth (2000)], and detected tiny seismic clusters using seismicity density. Then, we relocated earthquakes in each cluster with DD method using high-quality differential-time data derived from cross spectrum analysis. In addition, we read P-wave polarities and determined focal mechanism of earthquakes.
The obtained results show that normal-fault earthquakes lie above reverse fault earthquakes with a distance of 0.1 km. We interpreted that the pair of tensional and compressional stress regimes to be caused by the net volume reduction due to the phase transformation, as considered in Nakajima et al. (2013). Our finding provides new seismic evidence that the stress regime in the slab can be altered over a very small scale by phase-transformation-related stresses.