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

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doi: 10.1002/2016JB013417
Author(s): Wallace, L. M.; Araki, E.; Saffer, D.; Wang, X.; Roesner, A.; Kopf, A.; Nakanishi, A.; Power, W.; Kobayashi, R.; Kinoshita, C.; Toczko, S.; Kimura, T.; Machida, Y.; Carr, S.
Author Affiliation(s): Primary:
University of Texas at Austin, Institute for Geophysics, Austin, TX, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Pennsylvania State University, United States
GNS Science, New Zealand
University of Bremen, Germany
Kagoshima University, Japan
Kyoto University, Japan
Bigelow Laboratory for Ocean Sciences, United States
Volume Title: Journal of Geophysical Research: Solid Earth
Source: Journal of Geophysical Research: Solid Earth, 121(11), p.8338-8351. Publisher: Wiley-Blackwell for American Geophysical Union, Washington, DC, United States. ISSN: 2169-9313
Note: In English. 57 refs.; illus., incl. block diag., 1 table, geol. sketch maps
Summary: An Mw 6.0 earthquake struck ∼50 km offshore the Kii Peninsula of southwest Honshu, Japan on 1 April 2016. This earthquake occurred directly beneath a cabled offshore monitoring network at the Nankai Trough subduction zone and within 25-35 km of two borehole observatories installed as part of the International Ocean Discovery Program's NanTroSEIZE project. The earthquake's location close to the seafloor and subseafloor network offers a unique opportunity to evaluate dense seafloor geodetic and seismological data in the near field of a moderate-sized offshore earthquake. We use the offshore seismic network to locate the main shock and aftershocks, seafloor pressure sensors, and borehole observatory data to determine the detailed distribution of seafloor and subseafloor deformation, and seafloor pressure observations to model the resulting tsunami. Contractional strain estimated from formation pore pressure records in the borehole observatories (equivalent to 0.37 to 0.15 µstrain) provides a key to narrowing the possible range of fault plane solutions. Together, these data show that the rupture occurred on a landward dipping thrust fault at 9-10 km below the seafloor, most likely on the plate interface. Pore pressure changes recorded in one of the observatories also provide evidence for significant afterslip for at least a few days following the main shock. The earthquake and its aftershocks are located within the coseismic slip region of the 1944 Tonankai earthquake (Mw ∼8.0), and immediately downdip of swarms of very low frequency earthquakes in this region, illustrating the complex distribution of megathrust slip behavior at a dominantly locked seismogenic zone. Abstract Copyright (2016), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 19 Geophysics, Seismology; Aftershocks; Asia; Boreholes; Coseismic processes; Deformation; Earthquakes; Expedition 365; Far East; Faults; Geodetic networks; Honshu; IODP Site C0010; International Ocean Discovery Program; Japan; Kii Peninsula; Main shocks; NanTroSEIZE; Nankai Trough; Nankai earthquake 2016; North Pacific; Northwest Pacific; Offshore; Pacific Ocean; Pore pressure; Rupture; Seismic networks; Seismic zoning; Swarms; Thrust faults; West Pacific
Coordinates: N300000 N350000 E1400000 E1350000
N331236 N331236 E1364112 E1364112
Record ID: 2017010458
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom