摘要：On December 7, 2012, a pair of large Mw 7.2 intraplate earthquakes occurred near the Japan Trench axis off Miyagi, northeast Japan.This doublet consisted of a deep reverse-faulting event followed by a shallow normal-faulting event.Aftershock observations using conventional and newly developed ultra-deep ocean bottom seismographs in the trench axis area showed that the shallow normal-faulting event occurred in the subducting Pacific plate just landward of the trench axis.The shallow normal-faulting aftershock activity indicated that in-plate tension in the incoming/subducting Pacific plate extends to a depth of at least 30 km, which is deeper than before the 2011 Tohoku-Oki earthquake, whereas in-plate compression occurs at depths of more than 50 km.Hence, we concluded that the neutral plane of the in-plate stress is located between depths of 30 and 50 km near the trench axis.
关键词：Japan Trench ;Intraplate doublet ;Stress state ;Subduction zone ;2011 Tohoku-Oki earthquake
