Systematic changes in the incoming plate structure at the Kuril trench

Fujie, Gou; Kodaira, Shuichi; Yamashita, M; Sato, Takeshi; Takahashi, Tsutomu; Takahashi, Narumi

doi:10.1029/2012gl054340

Cited by 111 publications

(143 citation statements)

References 30 publications

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“…Deploying three-component, short-period (4.5 Hz) sensors with a station spacing of 6 km, we constructed six linear OBS arrays in the northwestern Pacific for seismic exploration surveys during 2009 and 2010 (Fujie et al 2013 …”

Section: Methodsmentioning

confidence: 99%

“…2c) by Fujie et al (2013). Fujie et al (2013) reported that the sub-seafloor structure in the southern part (x > 350 km) was formed near the spreading center and that the subseafloor structure around the region was deformed by magma-involved activity and normal faults during its formations. This explains the remarkably complex topography of the basement in the southern part, as shown in Fig.…”

Section: S Reflection Retrieval In the Northwestern Pacificmentioning

confidence: 99%

“…A post-stack time migration of multi-channel seismic (MCS) reflection survey data has been previously performed along A-A′ (Fig. 2c) by Fujie et al (2013). Fujie et al (2013) reported that the sub-seafloor structure in the southern part (x > 350 km) was formed near the spreading center and that the subseafloor structure around the region was deformed by magma-involved activity and normal faults during its formations.…”

Section: S Reflection Retrieval In the Northwestern Pacificmentioning

confidence: 99%

“…The time migration result (Fujie et al 2013) provides us information relevant to the two-way travel time of P-wave between the seafloor and basement. Using the two-way travel times of P and S reflections, we can estimate Vp/Vs within the marine sediments.…”

Section: Vp/vs Within Marine Sedimentsmentioning

confidence: 99%

“…Constraints of the P-wave velocity (Vp) structure at the shallow part of the plate have been accomplished by seismic refraction and reflection surveys focusing on structures beneath the seawater (Cadet et al, 1987;Shimamura et al 1983;Fujiwara et al, 2007;Shinohara et al 2008). S wave velocity (Vs) structures have also been well confined, particularly at depths shallower than the topmost of the oceanic mantle by active seismic surveys (Fujie et al, 2013). At greater depths, surface wave (Isse et al, 2009) and receiver function Kumar et al 2011) analyses have revealed Vs structure beneath the ocean.…”

Section: Introductionmentioning

confidence: 99%

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Geographical distribution of shear wave anisotropy within marine sediments in the northwestern Pacific

Tonegawa

Fukao

Fujie

et al. 2015

Prog. in Earth and Planet. Sci.

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In the northwestern Pacific, the elastic properties of marine sediments, including P-wave velocities (Vp) and S wave velocities (Vs), have recently been constrained by active seismic surveys. However, information on S anisotropy associated with the alignments of fractures and fabric remains elusive. To obtain such information, we used ambient noise records observed by ocean-bottom seismometers at 254 sites in the northwestern Pacific to calculate the auto-correlation functions for the S reflection retrieval from the top of the basement. For these S reflections, we measured differential travel times and polarized directions to reveal the potential geographical systematic distribution of S anisotropy. As a result, the observed differential times between fast and slow axes were at most 0.05 s. The fast polarization axes tend to align in the trench-parallel direction in the outer rise region. In particular, their directions changed systematically in accordance with the direction of the trench axis, which changes sharply across the junction of the Kuril and Japan trenches. We consider that a contributing factor for the obtained S anisotropy within marine sediments in the outer rise region is primarily aligned fractures due to the tensional stresses associated with the bending of the Pacific Plate. Moreover, numerical simulations conducted by using the three-dimensional (3D) finite difference method for isotropic and anisotropic media indicates that the successful extraction of S anisotropic information from the S reflection observed in this study is obtained from nearvertically propagating S waves due to extremely low Vs within marine sediments. In addition, we conducted an additional numerical simulation with a realistic velocity model to confirm whether S reflections below the basement can be extracted or not. The resultant auto-correlation function shows only S reflections from the top of the basement. It appears that such near-vertically propagating S waves obscure S reflections from interfaces below the basement.

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Section: Methodsmentioning

confidence: 99%

Section: S Reflection Retrieval In the Northwestern Pacificmentioning

confidence: 99%

Section: S Reflection Retrieval In the Northwestern Pacificmentioning

confidence: 99%

Section: Vp/vs Within Marine Sedimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geographical distribution of shear wave anisotropy within marine sediments in the northwestern Pacific

Tonegawa

Fukao

Fujie

et al. 2015

Prog. in Earth and Planet. Sci.

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Hydration adjacent to a deeply subducting slab: The roles of nominally anhydrous minerals and migrating fluids

Hebert

Montési

2013

JGR Solid Earth

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[1] Subduction-related transport of water into the mantle has significant dynamical and geochemical implications. Dehydration of hydrous phases within the slab can introduce water into the transition zone and lower mantle, potentially hydrating nominally anhydrous minerals (NAM) and impacting the viscosity and density structure of the mantle over a wide area. We present models of fluid transport and mantle hydration in the vicinity of a deeply subducting slab, focusing on the fate of water released by deep dehydration reaction in the subducted serpentinized mantle. A sharp decrease in water storage capacity across the lower boundary of the transition zone may produce "secondary dehydration" of hydrated NAM, leading to precipitation of a hydrous fluid and heterogeneous hydration of the transition zone. Rapid fluid migration relative to the solid flow field can lead to a broad region of diffuse hydration within the upper mantle wedge and the potential for localized melt regions at the top of the transition zone coincident with fluid pathways. Slower fluid migration instead implies that the fluid phase can be transported deep into the lower mantle. Water stabilized in NAM and as a free fluid can initiate upwelling within and above the transition zone. A less abrupt change in water storage capacity across the base of the transition zone leads to high NAM water contents in a channel adjacent to the slab where viscosity is reduced. However, seismic and electromagnetic observations of hydration in the transition zone are most compatible with a sudden drop of water storage capacity.Citation: Hebert, L. B., and L. G. J. Monte´si (2013), Hydration adjacent to a deeply subducting slab: The roles of nominally anhydrous minerals and migrating fluids,

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Structural heterogeneities around the megathrust zone of the 2011 Tohoku earthquake from tomographic inversion of onshore and offshore seismic observations

Yamamoto

Obana

Kodaira

et al. 2014

J. Geophys. Res. Solid Earth

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We performed a three-dimensional seismic tomography around the coseismic slip area of the 2011 Tohoku earthquake. By combining data from the aftershock period collected by ocean bottom seismographs (OBSs), OBS data from previous studies off the Miyagi coast, and land seismic data, we modeled the detailed seismic velocity structure along the plate boundary from the Japan Trench to near the coastline. Our results indicate that V P , V S , and V P /V S along the plate boundary change drastically about 60 km landward from the trench axis. Trenchward of this boundary, velocities are consistent with a fluid-rich environment (low V P and V S and high V P /V S ) associated with the occurrence of sediment compaction and opal-to-quartz metamorphism. This area also corresponds to the contact between the slab and upper crust or between the slab and the sediment layer. A comparison of our results with numerical simulations and geological studies suggests that thermal pressurization might have occurred near the trench axis during the 2011 Tohoku earthquake. To the west of this boundary, where V P , V S , and V P /V S have moderate values, our model showed small-scale heterogeneous structures in the subducted oceanic crust near the hypocenter of the Tohoku earthquake with regions of low and high V P /V S on the updip and downdip sides of the hypocenter, respectively. We interpret the former as corresponding to the strong coupling patch and the latter as the localized fluid-rich zone. Small-scale heterogeneities thus may affect the nucleation and rupture processes of large earthquakes.

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Systematic changes in the incoming plate structure at the Kuril trench

Cited by 111 publications

References 30 publications

Geographical distribution of shear wave anisotropy within marine sediments in the northwestern Pacific

Geographical distribution of shear wave anisotropy within marine sediments in the northwestern Pacific

Hydration adjacent to a deeply subducting slab: The roles of nominally anhydrous minerals and migrating fluids

Structural heterogeneities around the megathrust zone of the 2011 Tohoku earthquake from tomographic inversion of onshore and offshore seismic observations

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