Upper and middle crustal deformation of an arc–arc collision across Hokkaido, Japan, inferred from seismic refraction/wide-angle reflection experiments

Iwasaki, Takaya; Adachi, Kôichi; Moriya, Toshio; Miyamachi, Hiroki; Matsushima, Takeshi; Miyashita, Kencho; Takeda, Testsuya; Taira, T.; Yamada, Tomoaki; Ohtake, Kazuo

doi:10.1016/j.tecto.2004.03.025

Cited by 63 publications

(78 citation statements)

References 19 publications

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“…6). Lack of seismic activities in the colliding region of the two plates and high seismic activities in the front of a tip of the collision zone are also seen at the Hidaka Collision Zone, central Hokkaido, Japan (Iwasaki et al, 2004). In addition, Shinohara et al (2012) estimated several focal mechanisms of aftershocks, and there are earthquakes with a P-axis in the north-south direction in front of the uncertain region (Fig.…”

Section: Resultsmentioning

confidence: 92%

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

et al. 2012

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We present the result of a seismic experiment conducted using ocean bottom seismometers and controlled sources in the region off Ibaraki and the Boso Peninsula. This region is the southern edge of the rupture zone of the 2011 off the Pacific coast of Tohoku Earthquake. We estimated the P-wave seismic velocity structure beneath the profile using a 2-D ray-tracing method. The crustal structure in the southern area is more heterogeneous than that of the northern area. This heterogeneity is thought to be related with subducting the Philippine Sea plate (PHS). The plate boundary between the landward plate and the Pacific plate (PAC) is positioned at depths of 20 km at a distance of 170 km from the southern end of the profile. The subducting PHS is imaged on the southern part of the profile. However, we could not obtain a distinct image of the contact zone of PHS and PAC. The contact zone of PHS and PAC is estimated to have a large heterogeneity resulting from strong deformation due to the collision of the two plates. We infer that the termination of the rupture, and the large afterslip in the collision region, are caused by this strong heterogeneity.

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Section: Resultsmentioning

confidence: 92%

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

et al. 2012

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“…In the southern Hokkaido region of Japan, the Kuril arc has been colliding with the northeast Japan arc since middle Miocene [Kimura, 1994], resulting in the uplift of the Hidaka Mountains behind the Hidaka Main Thrust. Seismic tomographic and exploration studies confirm that the Kuril arc is obducted toward the west [Tsumura et al, 1999;Murai et al, 2003;Iwasaki et al, 2004]. Their results show that the lower crust of the Kuril arc is delaminated at a depth of 20 $ 30 km on the eastern side of the Hidaka Mountains and that the lower part is descending westward.…”

Section: Hokkaidomentioning

confidence: 92%

Three‐dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi‐net tiltmeters

2008

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[1] We developed a three-step method for three-dimensional (3-D) S wave velocity tomography by fitting synthetic cross spectra to the observed ones of ambient seismic noise. We applied this method to the recording of Hi-net tiltmeters in Japan at 679 stations from June 2004 to December 2004. First, we calculated normalized cross spectra between radial components and those between transverse components for every pair of stations. The first step is local 1-D S wave velocity inversion for each station assuming small lateral heterogeneity under a 100-km circle of a station. We measured the dispersion curves of fundamental Rayleigh waves, fundamental Love waves, and first overtone of Love waves by fitting the synthetic cross spectra to the observed ones between pairs of stations within the circle. We inverted the measured dispersion curves for obtaining a 1-D S wave velocity model. The second step is the inversion of the observed cross spectra for obtaining path-averaged 1-D S wave velocity structure. The third step is the inversion of the resultant path-averaged structures for obtaining 3-D S wave velocity structure (0.1°Â 0.1°Â 1 km grid from the surface to a depth of 50 km) using ray approximation. The resultant S wave velocity structures show clear low-velocity anomalies along tectonic lines from the surface to a depth of 20 km. In particular, along the Hidaka mountain range, we observed S wave perturbation more extreme than À20%. They also show low-velocity anomalies under volcanoes in Kyusyu and Tohoku. In the southwestern part of Shikoku, our results show a clear low-velocity anomaly corresponding to an accretional belt (Shimanto belt). Below 20 km, we observe a low-velocity anomaly in the center of Japan, which suggests a thick crust.Citation: Nishida, K., H. Kawakatsu, and K. Obara (2008), Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi-net tiltmeters,

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“…High temperature metamorphic rocks of Tertiary age are exposed and include materials from the upper and lower crust (e.g., Shimura et al, 2004). Ito (2000) and Iwasaki et al (2004) suggested this region is characterized by delamination of the lower crust, with partial exhumation of the lower crust, and partial subduction along the Pacific slab. The combination of inferences from local geology and tomographic imaging suggests that the presence of subducted fore-arc materials cause thermal shielding of the slab to greater depths than elsewhere.…”

Section: Seismicity and Thermal Structure At The Trench Junctionmentioning

confidence: 99%

Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

2012

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Abstract. The cause of intermediate-depth (> 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The wellinstrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediatedepth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths > 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by timedependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediatedepth seismicity.

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Upper and middle crustal deformation of an arc–arc collision across Hokkaido, Japan, inferred from seismic refraction/wide-angle reflection experiments

Cited by 63 publications

References 19 publications

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

Three‐dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi‐net tiltmeters

Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

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