Geometry of the Subducting Philippine Sea Plate and the Crustal and Upper Mantle Structure beneath Eastern Shikoku Island Revealed by Seismic Refraction/Wide-angle Reflection Profiling

Kurashimo, Eiji; Tokunaga, Masako; Hirata, Naoshi; Iwasaki, Takaya; Kodaira, Shuichi; Kaneda, Yasufumi; Itō, Kiyoshi; Nishida, Ryohei; Kimura, Shozo; Ikawa, Takeshi

doi:10.4294/zisin1948.54.4_489

Cited by 34 publications

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“…Although the possibility is not excluded that the reflections may come from the sides of the profile, because the area has a clear zonal arrangement and consistent strikes of the parallel fault zones, we suggests that reflectors dip in the same direction as the profile, which is perpendicular to the strike. Thus, we conclude that the origins of the major deep reflections on our seismic reflection line (L1, L2 and L3) are the major boundary faults (MTL, BTL and AF, re- Kurashimo et al (2002). Oceanic Crust (PHS) beneath Shikoku Island is after Kodaira et al (2000).…”

Section: Discussionmentioning

confidence: 71%

“…This suggests that the laminated zone between L4 and L5 is the lower crust, and that L5 is the Moho. The crustal structure beneath east Shikoku interpreted from the studies of this experiment (99MTL), 92MTL (Ito et al, 1996) and Kurashimo et al (2002) is shown in Fig. 7.…”

Section: Discussionmentioning

confidence: 98%

“…or more, we used the velocities that were estimated by the refraction survey (Kurashimo et al, 2002). Only elevation static corrections were applied because the weathering layer is too thin to require subsurface static corrections.…”

Section: Discussionmentioning

confidence: 99%

“…6). According to the seismic refraction study by Kurashimo et al (2002) along A-A in Fig. 1, the zone between L4 and L5 has a seismic velocity of 6.6 km/s and L5 approximately corre- sponds to a velocity boundary jumping from 6.6 to 7.8 km/s.…”

Section: Discussionmentioning

confidence: 99%

“…The Shi- (Ito et al, 1996) and 99MTL (this study). Shaded lines ES99 and KY9903 correspond to the seismic lines of Kurashimo et al (2002) and Kodaira et al (2000) Katto, 1961) between the Northern Shimanto and the Southern Shimanto subbelts. The present subduc- Mizuno et al (1993) and Tsukuda et al (1982).…”

Section: Surface Structurementioning

confidence: 99%

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Deep seismic reflection experiment using a dense receiver and sparse shot technique for imaging the deep structure of the Median Tectonic Line (MTL) in east Shikoku, Japan

Kawamura

Onishi²,

Kurashimo

et al. 2014

Earth Planet Sp

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A seismic experiment was carried out in east Shikoku, Japan, to detect deep reflections across the Median Tectonic Line (MTL), which juxtaposes low-P/T metamorphic rocks with high-P/T metamorphic rocks. Our experiment employed an unconventional technique: sparse shot spacing, a strong energy source (dynamite) and a dense array of seismometers. The above specifications produce only single fold coverage without common midpoint (CMP) stacking. Nevertheless, the reflection profile provides essential information on the deep structure of the MTL, of other major faults, and of the Moho in east Shikoku. On the MTL, this profile is the first to delineate the MTL from the surface to about 12 km depth. The following three factors were essential to the success of our experiment. First, the receiver interval was sufficiently small to provide horizontal resolution that was able to detect deep reflectors. Second, the simple crustal structure does not require CMP stacking to enhance data quality. Third, a thin weathering layer at the surface reduced the attenuation of seismic waves and minimized the generation of the surface waves that often obscure deep reflectors. In these conditions, the technique can be an effective means of probing the deep crust while substantially reducing survey costs.

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Surface Structurementioning

confidence: 99%

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Deep seismic reflection experiment using a dense receiver and sparse shot technique for imaging the deep structure of the Median Tectonic Line (MTL) in east Shikoku, Japan

Kawamura

Onishi²,

Kurashimo

et al. 2014

Earth Planet Sp

Self Cite

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Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone

Kita

Matsubara

2016

JGR Solid Earth

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The three‐dimensional seismic attenuation structure (frequency‐independent Q) beneath southwestern Japan was analyzed using t* estimated by applying the S coda wave spectral ratio method to the waveform data from a dense permanent seismic network. The seismic attenuation (Qp−1) structure is clearly imaged for the region beneath Shikoku, the Kii peninsula, and eastern Kyushu at depths down to approximately 50 km. At depths of 5 to 35 km, the seismic attenuation structure changes at the Median tectonic line and other geological boundaries beneath Shikoku and the southwestern Kii peninsula. High‐Qp zones within the lower crust of the overlying plate are found just above the slip regions at the centers of the long‐term slow‐slip events (SSEs) beneath the Bungo and Kii channels and central Shikoku. Beneath central Shikoku, within the overlying plate, a high‐Qp zone bounded by low‐Qp zones is located from the land surface to the plate interface of the subducting plate. The high‐Qp zone and low‐Qp zones correspond to high‐Vp and low‐Vp zones of previous study, respectively. The boundaries of the high‐ and low‐Qp zones are consistent with the segment boundaries of tremors (segment boundaries of short‐term SSEs). These results indicated that the locations of the long‐ and short‐term SSEs could be limited by the inhomogeneous distribution of the materials and/or condition of the overlying plate, which is formed due to geological and geographical process. The heterogeneity of materials and/or condition within the fore‐arc crust possibly makes an effect on inhomogeneous rheological strength distribution on the interface.

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Topography of the Seismic Velocity Discontinuities beneath the Chugoku and Shikoku Districts, Southwest Japan

Oda

Okamoto

Ishise

2005

Pure appl. geophys.

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The first P-arrival-time data from 513 local earthquakes were analyzed to study lateral variation of the depth to the Conrad and Moho discontinuities beneath the Chugoku and Shikoku districts, southwest Japan, as well as to determine earthquake hypocenters and P-wave station corrections. The depth to the discontinuity was estimated by minimizing the travel-time residuals of more than 8700 first P arrivals observed at 55 seismic stations. The Conrad and Moho discontinuities are located within depth ranges of 15-25 km and 30-40 km, respectively. The Moho is deeper under the mountain area than under the Seto Inland Sea area, and especially deep under the Pacific Coast of the Shikoku district and the mountain area in the Chugoku district. The depth variation of the Moho is quite similar to the Bouguer gravity anomaly distribution and the lateral variations of the P-wave velocity. The deep Moho under the southern Shikoku is located at the portion in which the continental Moho under the island arc meets the oceanic Moho that is the boundary interface between the oceanic crust and the Philippine Sea (PHS) plate dipping toward the back arc. Although there are high mountains in the northern and middle Shikoku, the Moho is not so deep because subduction of the PHS plate prevents the Moho from getting deep, while the Moho is deep due to isostatic balance under the mountain area in the Chugoku district. In addition, we indicated the possibility that the upper boundary of the oceanic crust just above the high-velocity PHS plate is in contact with the deep Moho under the western Chugoku. The contact of the Moho with the oceanic crust can explain the markedly negative gravity anomaly observed in the western Chugoku and the later phase that appears just after the first P arrival from local earthquakes.

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Geometry of the Subducting Philippine Sea Plate and the Crustal and Upper Mantle Structure beneath Eastern Shikoku Island Revealed by Seismic Refraction/Wide-angle Reflection Profiling

Cited by 34 publications

References 0 publications

Deep seismic reflection experiment using a dense receiver and sparse shot technique for imaging the deep structure of the Median Tectonic Line (MTL) in east Shikoku, Japan

Deep seismic reflection experiment using a dense receiver and sparse shot technique for imaging the deep structure of the Median Tectonic Line (MTL) in east Shikoku, Japan

Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone

Topography of the Seismic Velocity Discontinuities beneath the Chugoku and Shikoku Districts, Southwest Japan

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