Interseismic seafloor crustal deformation immediately above the source region of anticipated megathrust earthquake along the Nankai Trough, Japan

Tadokoro, K.; Ikuta, Ryoya; Watanabe, Tsuyoshi; Ando, Masataka; Okuda, Takashi; Nagai, Sakahisa; Yasuda, Katsutaro; Sakata, Toyohiro

doi:10.1029/2012gl051696

Cited by 35 publications

(43 citation statements)

References 31 publications

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“…Earthquakes are scattered mainly in the oceanic crust and uppermost mantle, and there are very few events along the plate boundary. Low seismicity at the plate boundary may reflect a strong coupling ratio (> 80%) between the plates in this region (e.g., Tadokoro et al, 2012;Yoshioka and Matsuoka, 2013). Northeast-southwest cross sections (almost parallel to the trough axis) show the seismicity separated into a southwestern and a northeastern cluster (Fig.…”

Section: Seismic Activity Along the Nankai Troughmentioning

confidence: 96%

Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Nakamura¹,

Kaneda²

2015

Bulletin of the Seismological Society of America

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We investigated the hypocenter distribution along the Nankai trough off the Kii Peninsula, Japan, by using data from both ocean-bottom and land-based seismic networks. Because seismic velocity structures differ greatly below land and ocean, we used a 3D velocity model based on a structural model of the Philippine Sea plate (PHS), which provides much more accurate estimations of source locations than 1D velocity models derived from either onshore or ocean-bottom seismic data alone, especially for sources between the coast and the trough axis. We identified intensive seismic activity below the axis of the Nankai trough, which we interpreted to be aftershocks of the 2004 Off the Kii Peninsula earthquakes (M JMA 7.1, 7.4, and 6.5), but found much less seismic activity along the subducting PHS. The earthquake sources below the trough axis lie on dipping planes within the PHS, from which we inferred that a fracture zone is developing within the PHS. Our estimated focal mechanisms for these earthquakes showed that their P axes were oriented north-south to northeast-southwest, similar to those of the 2004 events, which were rotated clockwise by 45°-90°from the northwest-southeast direction of convergence between the PHS and the Eurasian plates. We consider that the fracture zone represents a boundary between the PHS and the Izu microplate, which are converging in a north-south direction, and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates.

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Section: Seismic Activity Along the Nankai Troughmentioning

confidence: 96%

Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Nakamura¹,

Kaneda²

2015

Bulletin of the Seismological Society of America

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“…The subducting seamount (Kodaira et al 2000) and the Paleo-Zenisu and deeper Paleo ridges Park et al 2003) are shown by light blue regions. The light blue and red arrows indicate the seafloor velocity vectors observed by Nagoya University (Tadokoro et al 2012) and the authors, respectively.…”

Section: Competing Interestsmentioning

confidence: 88%

“…Our past observations near the Japan Trench provided great advantage in understanding the 2005 Off-Miyagi Prefecture earthquake (M7.2) (e.g., Matsumoto et al 2006 andSato et al 2011b), the 2011 Tohoku-oki earthquake (M9.0) (e.g., Sato et al 2011a andSato et al 2013b), and others. Important observations have also been made by other research groups in Japan such as Tohoku University (e.g., Kido et al 2006 andKido et al 2011) and Nagoya University (e.g., Tadokoro et al 2012 andYasuda et al 2014).…”

Section: Seafloor Geodetic Observation Using a Gps-acoustic Combinatimentioning

confidence: 94%

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Heterogeneous interplate coupling along the Nankai Trough, Japan, detected by GPS-acoustic seafloor geodetic observation

Yokota

Ishikawa

Sato

et al. 2015

Prog. in Earth and Planet. Sci.

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The recurring devastating earthquake that occurs in the Nankai Trough subduction zone between the Philippine Sea plate and the Eurasian plate has the potential to cause an extremely dangerous natural disaster in the foreseeable future. Many previous studies have assumed interplate-coupling ratios for this region along the trench axis using onshore geodetic data in order to understand this recursive event. However, the offshore region that has the potential to drive a devastating tsunami cannot be resolved sufficiently because the observation network is biased to the land area. Therefore, the Hydrographic and Oceanographic Department of Japan constructed a geodetic observation network on the seafloor along the Nankai Trough using a GPS-acoustic combination technique and has used it to observe seafloor crustal movements directly above the Nankai Trough subduction zone. We have set six seafloor sites and cumulated enough data to determine the displacement rate from 2006 to January 2011. Our seafloor geodetic observations at these sites revealed a heterogeneous interplate coupling that has three particular features. The fast displacement rates observed in the easternmost area indicate strong interplate coupling (>75%) around not only the future Tokai earthquake source region but also the Paleo-Zenisu ridge. The slow displacement rates near the trench axis in the Kumano-nada Sea, a shallow part of the 1944 Tonankai earthquake source region, show a lower coupling ratio (50% to 75%). The slow displacement rate observed in the area shallower than the 1946 Nankaido earthquake source region off Cape Muroto-zaki reflects weakening interplate coupling (about 50%) probably due to a subducting seamount. Our observations above the subducting ridge and seamount indicate that the effect of a subducting seamount on an interplate-coupling region depends on various conditions such as the geometry of the seamount and the friction parameters on the plate boundary.

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“…In Japan, our group first succeeded in detecting seafloor movements caused by interseismic plate convergence at the Japan Trench ) and has continued to monitor the movements including coseismic and postseismic deformation at the seafloor sites along the Japan Trench (e.g., Matsumoto et al 2006;Sato et al 2011a, b;Sato et al 2013b;Watanabe et al 2014) and the Nankai Trough (e.g., Yokota et al 2015). Moreover, other groups in Japan have provided important results (Kido et al 2006;Kido et al 2011;Tadokoro et al 2012;Yasuda et al 2014) to understand the major interplate earthquakes as well. Figure 1 shows a schematic picture of the GPSacoustic positioning system developed by our group.…”

Section: Methods and Observation Datamentioning

confidence: 97%

Non-volcanic crustal movements of the northernmost Philippine Sea plate detected by the GPS-acoustic seafloor positioning

2015

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Repeatedly performing the GPS-acoustic seafloor positioning, we first succeeded in detecting non-volcanic seafloor movements on the Philippine Sea plate (PHS) subducting along the Sagami Trough. At a seafloor geodetic site on the northernmost part of the PHS off the Boso Peninsula, we detected significant eastward motion with respect to the central part of the PHS. This is unaccountable by the coupling between the Pacific plate and the PHS along the Izu-Bonin (Ogasawara) Trench because it would cause the westward elastic deformation at BOSS. It is rather consistent with the rigid motion of the tectonic block in the fore-arc along the Izu-Bonin Trench, associated with the back-arc rift. The other site on the western side of the Sagami Bay had moved toward the north relative to the Izu Peninsula. It suggests that the Izu microplate obviously moves relative to the northern PHS. The difference between the velocities of the Sagami Bay and the Izu Peninsula indicates the coupling on the boundary fault as well.

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Interseismic seafloor crustal deformation immediately above the source region of anticipated megathrust earthquake along the Nankai Trough, Japan

Cited by 35 publications

References 31 publications

Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Heterogeneous interplate coupling along the Nankai Trough, Japan, detected by GPS-acoustic seafloor geodetic observation

Non-volcanic crustal movements of the northernmost Philippine Sea plate detected by the GPS-acoustic seafloor positioning

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