Abstract
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.
Highlights
On December 7, 2012, a pair of large intraplate earthquakes occurred at the Japan Trench off Miyagi, northeast Japan (Figure 1)
The length of this lineation was consistent with a finite fault slip model of the shallow normal-faulting earthquake of the 2012 Japan Trench doublet obtained from a teleseismic body wave inversion (Harada et al 2013)
Lay et al (2013) estimated the location of the shallow normal-faulting event to be east of the Japan Trench based on a two double-couple W-phase inversion, the GCMT solution was located within the uncertainty of the W-phase inversion
Summary
On December 7, 2012, a pair of large intraplate earthquakes occurred at the Japan Trench off Miyagi, northeast Japan (Figure 1). The centroid depths of these events were 57.8 and 19.5 km This intraplate doublet generated a tsunami, which was observed along the Pacific coast of northeast Japan with a maximum height of about 1 m (Japan Meteorological Agency 2012). This doublet occurred seaward of the largest coseismic slip area during the 2011 Mw 9.0 Tohoku-Oki earthquake. Since the 2011 Mw 9.0 Tohoku-Oki earthquake, shallow normal-faulting seismicity has been active in the incoming/subducting Pacific plate near the Japan Trench (e.g., Asano et al 2011) This normal-faulting earthquake activity was enhanced by the
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