Near‐field observations of an offshore Mw 6.0 earthquake from an integrated seafloor and subseafloor monitoring network at the Nankai Trough, southwest Japan

• DOI: 10.1002/2016jb013417
• Publication Date: 2016-10-19T18:34:57Z
• Authors: L. M. Wallace; E. Araki; D. Saffer; X. Wang; A. Roesner; A. Kopf; A. Nakanishi; W. Power; R. Kobayashi; C. Kinoshita; S. Toczko; T. Kimura; Y. Machida; S. Carr
• Keywords: Seafloor Spreading

Abstract An M w 6.0 earthquake struck ~50 km offshore the Kii Peninsula of southwest Honshu, Japan on 1 April 2016. This occurred directly beneath a cabled monitoring network at Nankai Trough subduction zone and within 25–35 two borehole observatories installed as part International Ocean Discovery Program's NanTroSEIZE project. The earthquake's location close to seafloor subseafloor offers unique opportunity evaluate dense geodetic seismological data in near field moderate‐sized earthquake. We use seismic locate main shock aftershocks, pressure sensors, observatory determine detailed distribution deformation, observations model resulting tsunami. Contractional strain estimated from formation pore records (equivalent 0.37 0.15 μstrain) provides key narrowing possible range fault plane solutions. Together, these show that rupture landward dipping thrust 9–10 below seafloor, most likely plate interface. Pore changes recorded one also provide evidence for significant afterslip least few days following shock. its aftershocks are located coseismic slip region 1944 Tonankai ( ~8.0), immediately downdip swarms very low frequency earthquakes this region, illustrating complex megathrust behavior dominantly locked seismogenic zone.