Interplate locking condition derived from seafloor geodetic observation in the shallowest subduction segment at the Central Nankai Trough, Japan

Yasuda, Katsutaro; Taniguchi, Sota; Kimura, Hiroshi; Matsuhiro, Kenjiro

doi:10.1002/2017gl072918

Cited by 39 publications

(56 citation statements)

References 14 publications

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“…It was inevitable to postulate that the faults have uniform coupling in our forward modeling under the present constraint of less spatial resolution, and it is clear that an extended observation network would enable us to depict a detailed spatial distribution of coupling ratios. The seafloor benchmarks installed at 15–20 km from the trench/trough axis contributed significantly to resolving the interplate coupling conditions in the vicinity of the Peru‐Chile Trench axis (Gagnon et al, ) and the Nankai Trough axis (Kimura et al, ; Yasuda et al, ). Therefore, it is necessary to install additional seafloor benchmarks in the vicinity of the Nansei‐Shoto Trench axis in order to derive the coupling condition there.…”

Section: Discussionmentioning

confidence: 99%

Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Nakamura

Ando

Kimura

et al. 2018

Geophysical Research Letters

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We performed observations of seafloor crustal deformation employing the Global Navigation Satellite System/Acoustic technique at two stations installed at about 45 and 70 km from the axis of the Nansei‐Shoto (Ryukyu) Trench, to the southeast off the Okinawa Main Island. The observations for 3‐ and 6‐year survey periods indicate that the two stations moved landward, in the opposite direction to the trench, by 63 and 21 mm/year relative to the Ryukyu Arc, suggesting interplate coupling around the stations. The observational results reveal the strong coupling state on the plate interface with coupling ratios of 0.9–1.0 at the slab depths of 10–13 km or 0.7–0.8 at slab depth ranging from 13 km up to the seafloor. The strongly coupled segment completely coincides with the source area of the 1791 tsunami event and does not overlap with the activity area of slow slip events.

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Section: Discussionmentioning

confidence: 99%

Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Nakamura

Ando

Kimura

et al. 2018

Geophysical Research Letters

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“…However, given that our data are only somewhat capable of determining w , we adopted this as an appropriate and practical measure for a more robust determination. Yasuda et al () adopted essentially the same measures and utilized variations in the travel time delay associated with the ship movement for determination of w .…”

Section: Analysis Methodsmentioning

confidence: 99%

“…Yasuda et al () and Yokota et al () both took a step‐by‐step approach in which the unknowns in the problem, such as the array or PXP position, temporal variation of the sound speed, and horizontal gradient of the sound speed, are determined individually in each step. With this approach, however, a certain solution can be obtained even for indefinite problems.…”

Section: Analysis Methodsmentioning

confidence: 99%

Offshore Postseismic Deformation of the 2011 Tohoku Earthquake Revisited: Application of an Improved GPS‐Acoustic Positioning Method Considering Horizontal Gradient of Sound Speed Structure

et al. 2019

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One of the important issues on the GPS‐acoustic (GPS‐A) observation for sea bottom positioning is how to address the horizontal heterogeneity of the sound speed in oceans. This study presents an analysis method of GPS‐A data in the presence of a sloping sound speed structure. By applying this method and revising the analysis scheme to make full use of existing data, we reevaluated the horizontal postseismic deformations occurring ~1.5–5 years after the 2011 Tohoku earthquake. The revised horizontal movements have more uniform directions and rates between neighboring sites, suggesting enhancement of the array positioning accuracy. The revised displacement rate of the site on the incoming Pacific plate, located ~100 km northeast of the main rupture zone, was decreased significantly; it was only slightly, by 1.4 cm/year larger than the global motion of the Pacific plate, suggesting a relatively small effect of viscoelastic relaxation. The horizontal movements of the near‐trench sites above the main rupture zone were generally landward and were significantly faster than the Pacific plate motion, indicating a viscoelastic relaxation of 5–10 cm/year. The distribution of the fast landward movements peaked near 38°N at an updip of the mainshock hypocenter and extended significantly farther to the north than to the south. This implies the existence of a secondary coseismic slip patch in the northern area in addition to a primary slip patch at ~38°N. The occurrence of episodic slow slip in early 2015 to the north of the main rupture zone was also verified from the GPS‐A analyses.

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“…For coseismic steps of the M 9 Tohoku‐Oki earthquake, we calculated the elastic deformation on the surface assuming an elastic half‐space and using the subfault model of Geospatial Information Authority of Japan (). For the postseismic deformation of the M 9 Tohoku‐Oki earthquake, we calculated the averaged displacement based on GEONET sites along the coastal area of Kumano Basin in the Kii Peninsula, using the combined logarithmic and exponential function model of Tobita () (Yasuda et al, ). Mean uncertainties in the east and north components for the GNSS/A sites managed by Nagoya University were 9.9 and 10.2 mm/year, respectively.…”

Section: Crustal Deformation Datamentioning

confidence: 99%

“…In Japan, an onshore continuous crustal deformation observation system using the Global Navigation Satellite System (GNSS) has been operated by the Geospatial Information Authority of Japan since 1996 (e.g., 10.1029/2018JB016159 Sagiya et al, 2000). In addition, recent campaign seafloor geodetic observations using the GNSS/Acoustic combination technique (hereinafter, GNSS/A; e.g., Fujita et al, 2006;Kido et al, 2006;Spiess et al, 1998;Tadokoro et al, 2006) has been operated in offshore regions by universities and the Japan Coast Guard (e.g., Chen et al, 2017;Tadokoro et al, 2006;Tomita et al, 2017;Yasuda et al, 2014Yasuda et al, , 2017Yokota et al, 2016). These observations can detect not only coseismic or postseismic displacements associated with earthquakes but also steady interseismic displacement.…”

Section: Introductionmentioning

confidence: 99%

Interplate Coupling Distribution Along the Nankai Trough in Southwest Japan Estimated From the Block Motion Model Based on Onshore GNSS and Seafloor GNSS/A Observations

Kimura

Itô

2019

JGR Solid Earth

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Along the Nankai Trough of southwest Japan, large‐magnitude interplate earthquakes (M > 8) have occurred repeatedly, with recurrence intervals of approximately 100 years. It is essential to estimate more precisely the spatial distribution of interplate coupling; that is, along‐strike and along‐dip heterogeneity of the coupling ratio defined as the slip deficit rate divided by the plate convergence rate, for understanding the mechanisms and/or assessing the potential of future mega interplate earthquakes in this region. Recently, the seafloor Global Navigation Satellite System‐Acoustic (GNSS/A) combination technique observation network has been extended, and we can now obtain crustal displacement fields for both onshore and offshore regions. In this study, we estimate interplate coupling distribution along the Nankai Trough using both seafloor GNSS/A and onshore GNSS data with the block motion model, minimizing the spatial variations of modeling uncertainties of coupling estimates. Seafloor GNSS/A data depict very strong coupling near the trough axis off of Tokai, as well as trough‐parallel heterogeneity in interplate coupling at the shallow plate interface. Using the block motion model confirmed that observed crustal deformation above the deep plate interface in SW Japan is dominated by rigid block motion rather than elastic response to slip deficit on the deep plate interface of the subducting Philippine Sea plate. The minimization of spatial variations for the modeling uncertainties of coupling estimates helps us to estimate the coupling distribution with nearly homogeneous uncertainties between offshore and onshore regions, which is useful for evaluation of interplate earthquakes and/or tsunamis hazards.

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Interplate locking condition derived from seafloor geodetic observation in the shallowest subduction segment at the Central Nankai Trough, Japan

Cited by 39 publications

References 14 publications

Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

Offshore Postseismic Deformation of the 2011 Tohoku Earthquake Revisited: Application of an Improved GPS‐Acoustic Positioning Method Considering Horizontal Gradient of Sound Speed Structure

Interplate Coupling Distribution Along the Nankai Trough in Southwest Japan Estimated From the Block Motion Model Based on Onshore GNSS and Seafloor GNSS/A Observations

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