Interaction between two subducting plates under Tokyo and its possible effects on seismic hazards

Wu, Francis T.; Okaya, D. A.; Sato, Hiroshi; Hirata, Naoshi

doi:10.1029/2007gl030763

Cited by 27 publications

(22 citation statements)

References 21 publications

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“…A small yet persistent feature is the low velocity zone above the Wadati‐Benioff zone in profile NS02 (blue arrow near the inverted triangular area in NS02, Figure 11) and in NS03 as well. Similarly positioned features with respect to the subduction zone have been mapped under Alaska [ Eberhart‐Phillips et al , 2006], New Zealand [ Eberhart‐Phillips and Reyners , 1997], and under Kanto, Japan, where the PSP subducts under the EUR [ F. T. Wu et al , 2007]. The strong coupling of the subducting plate with the upper plate may have dragged the latter down with it [ F. T. Wu et al , 2007].…”

Section: Resultsmentioning

confidence: 99%

Three‐dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets

Kuo-Chen¹,

Wu²,

Roecker³

2012

J. Geophys. Res.

133

178

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The convergence of the Philippine Sea and the Eurasian plates in the Taiwan region led to the formation of a young collisional mountain between two subduction zones of nearly orthogonal polarities. The geological processes underlying the collision and its relation to subduction are the primary targets of TAIGER (Taiwan Integrated Geodynamic Research) project. Newly acquired passive and active sources data on land, supplemented by ocean bottom as well as permanent seismic network data, are used to derive a new 3‐D tomographic velocity model. Using the 7.5 km/sec contour as a marker for crustal deformation, two trend‐parallel “roots,” one under the Central Range with a maximum depth of 55 km and the other under the Coastal Range at 40 km, are found to extend from southern to central (∼24°N) Taiwan. Between the two roots and lying approximately beneath the Longitudinal Valley, the 7.5 km/sec contour rises to 25 km depth. In the upper mantle, a high velocity zone, east‐dipping and its upper surface coinciding with a Wadati‐Benioff zone in the south (∼22.8°N), becomes near vertical and ill‐defined in the north (∼23.9°N). The crustal deformation as defined by the “roots” and the along‐trend variations of the upper mantle structures under Taiwan provide key information for the orogeny. With the thickening of crust to 55 km or more processes such as eclogitization and delamination may come into play.

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Section: Resultsmentioning

confidence: 99%

Three‐dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets

Kuo-Chen¹,

Wu²,

Roecker³

2012

J. Geophys. Res.

133

178

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“…Here we focus on heterogeneous structures related to the subduction of the PHS and PAC slabs. A characteristic E–W trending low‐velocity zone (pink arrows) exists beneath Kanto at depths of 25 and 40 km, which has been interpreted to be the crust of the PHS slab [e.g., Ohmi and Hurukawa , 1996; Sekiguchi , 2001], serpentinized mantle wedge in the overlying continental plate [ Kamiya and Kobayashi , 2000; Matsubara et al , 2005], or lower crustal materials dragged downward by the tectonic erosion of the continental plate due to the subduction of the PHS slab [ Wu et al , 2007]. An S wave low‐velocity anomaly subparallel to the volcanic front is imaged in the back‐arc side of northeastern (NE) Japan at depths of 40–140 km, which gradually shifts to the west with increasing depths.…”

Section: Slab Geometry 3‐d Seismic Velocity Structure and Slab Contmentioning

confidence: 99%

Seismotectonics beneath the Tokyo metropolitan area, Japan: Effect of slab‐slab contact and overlap on seismicity

Hirose²,

2009

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[1] We first determine the configuration of the upper surface of the Pacific (PAC) slab beneath Kanto, Japan, from the distribution of interplate earthquakes relocated by an appropriate 1-D velocity model. Then, traveltime tomography is carried out to estimate three-dimensional seismic velocity structures around Kanto using 735,520 P wave and 444,049 S wave arrival times from 6508 local earthquakes. The obtained results suggest that the Philippine Sea (PHS) slab is subducting to depths of 130-140 km without a gap, even to the northwest of the Izu collision zone. We subsequently define the lateral extent of the contact zone between the bottom of the PHS slab and the upper surface of the PAC slab (PHS-PAC interface) and reveal that the slab contact zone underlies a wider area beneath Kanto in harmony with the Kanto plain. The downdip limit of interplate (thrust-type) earthquakes on the PAC slab is deepened by $30 km locally under the slab contact zone. This deepening is probably caused by a lower-temperature environment in the PAC slab, resulting from the overlap with the PHS slab subducting above and consequent thermal shielding by the PHS slab from the hot mantle wedge. We detect an extremely low-velocity anomaly in the easternmost portion of the PHS slab, which is probably attributable to serpentinization of mantle peridotite. Interplate earthquakes are almost absent along the PHS-PAC interface overlain by the serpentinized mantle in the PHS slab, suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine.Citation: Nakajima, J., F. Hirose, and A. Hasegawa (2009), Seismotectonics beneath the Tokyo metropolitan area, Japan: Effect of slab-slab contact and overlap on seismicity,

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“…Consequently, there exist three types of slab interfaces beneath Kanto: between the overlying continental and the Pacific plates, between the continental and the Philippine Sea plates, and between the Philippine Sea and the Pacific plates (Figure 1c). The lateral extent of the interface between the Philippine Sea and the Pacific plates has been inferred from seismological observations, and seismic activity beneath Kanto has been explained in terms of slab‐slab contact [e.g., Huchon and Labaume , 1989; Okada and Kasahara , 1990; Ishida , 1992; Sekiguchi , 2001; Matsubara et al , 2005; Hori , 2006; Hasegawa et al , 2007; Wu et al , 2007]. …”

Section: Tectonic Framework Around the Kanto Regionmentioning

confidence: 99%

Cause of M ∼ 7 intraslab earthquakes beneath the Tokyo metropolitan area, Japan: Possible evidence for a vertical tear at the easternmost portion of the Philippine Sea slab

Nakajima¹,

Hasegawa²

2010

J. Geophys. Res.

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We perform travel‐time tomography beneath Kanto, Japan, to obtain detailed structures of the wedge‐shaped serpentinized mantle previously observed in the Philippine Sea slab. The results suggest that the western boundary of the serpentinized mantle (serpentine boundary) is subvertical and P‐ and S‐wave velocities vary by 15%–20% across it over the short distance of ∼10 km. Two intraslab earthquakes, in 1921 (M7.0) and 1987 (east off Chiba earthquake; M6.7), are inferred to have occurred along the serpentine boundary, accompanied by right‐lateral movement, based on analyses of focal mechanisms and aftershock distribution. A subvertical earthquake cluster penetrating the entire Philippine Sea slab is observed along the serpentine boundary, and four earthquakes in the cluster have strike‐slip focal mechanisms similar to that of the 1987 earthquake. Focal mechanisms obtained for past large earthquakes and present‐day microearthquakes suggest a concentration of right‐lateral deformation along the mechanically weak serpentine boundary. The Philippine Sea slab may have been torn in two along this boundary, with the eastern portion being left behind relative to subduction of the western portion. Assuming that one of the large aftershocks (M7.1) of the 1923 Kanto earthquake (M7.9), which occurred off the Boso Peninsula, ruptured the same asperity as did the 1987 earthquake, the slip deficit accumulated along the serpentine boundary during the 64 year interval is consistent with the fault slip of the 1987 earthquake. Interaction between the seismic slip along the plate interface and the serpentine boundary can explain the series of M7‐class earthquakes before and after the 1923 Kanto earthquake.

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Interaction between two subducting plates under Tokyo and its possible effects on seismic hazards

Cited by 27 publications

References 21 publications

Three‐dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets

Three‐dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets

Seismotectonics beneath the Tokyo metropolitan area, Japan: Effect of slab‐slab contact and overlap on seismicity

Cause of M ∼ 7 intraslab earthquakes beneath the Tokyo metropolitan area, Japan: Possible evidence for a vertical tear at the easternmost portion of the Philippine Sea slab

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