Existence of interplane earthquakes and neutral stress boundary between the upper and lower planes of the double seismic zone beneath Tohoku and Hokkaido, northeastern Japan

Kita, S.; Okada, Tomomi; Hasegawa, Akira; Nakajima, Jun; Matsuzawa, Toru

doi:10.1016/j.tecto.2010.10.010

Cited by 77 publications

(119 citation statements)

References 36 publications

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“…2 is based on independent thermal-petrological modeling and is not a fit to the observed seismicity. This independent correlation suggests the hypothesis that, at least in cold subduction zones, the upper Zhao et al, 1997;Kita et al, 2010b). Heat flow (Tanaka et al, 2004) is shown with the colored circles.…”

Section: Introductionmentioning

confidence: 75%

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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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Section: Introductionmentioning

confidence: 75%

“…1). For each cross section we determine the slab surface geometry from the 3-D slab surface geometry provided by Zhao et al (1997) and Kita et al (2010b) (Fig. 1).…”

Section: Modeling Approachmentioning

confidence: 99%

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

2012

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“…The gray arrows illustrate the background stress field in the subducting plate. The gray dashed line indicates the neutral stress plane by Kita et al (2010). The protractor indicates the angle from the subducting plate interface.…”

Section: Gps Data and Processingmentioning

confidence: 99%

“…The earthquake mechanism is estimated by NIED. The thin dashed line shows the subducting Pacific plate interface isodepth contours compiled by Kita et al (2010). Each dashed line represents 10-km intervals.…”

Section: Introductionmentioning

confidence: 99%

Large intraslab earthquake (2011 April 7, M 7.1) after the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0): Coseismic fault model based on the dense GPS network data

et al. 2011

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We propose a source fault model for the 2011, April 7, earthquake (M 7.1) deduced from a dense GPS network. The coseismic displacements obtained by GPS data analysis clearly show the spatial pattern specific to intraslab earthquakes, not only in the horizontal components but also the vertical ones. A rectangular fault with uniform slip was estimated by a non-linear inversion approach. The results indicate that the simple rectangular fault model can explain the overall features of the observations. The amount of moment released is equivalent to M w 7.17. The hypocenter depth of the main shock estimated by the Japan Meteorological Agency is slightly deeper than the neutral plane between down-dip compression (DC) and down-dip extension (DE) stress zones of the doubleplaned seismic zone. This suggests that the depth of the neutral plane was deepened by the huge slip of the 2011, M 9.0, Tohoku Earthquake, and the rupture of the thrust M 7.1 earthquake was initiated at that depth, although more investigations are required to confirm this idea. The estimated fault plane has an angle of ∼60 degrees from the surface of the subducting Pacific plate. It is consistent with the hypothesis that intraslab earthquakes are thought to be a reactivation of the pre-existing hydrated weak zones produced in the bending process of oceanic plates around outer-rise regions.

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“…The red star indicates the epicenter of the mainshock determined by the Japan Meteorological Agency. The thin dashed line shows isodepth contours of the subducting Pacific plate interface at 10 km intervals compiled by Kita et al (2010). Colored contours indicate the spatial distribution of past earthquake source regions estimated by Yamanaka and Kikuchi (2004).…”

Section: Instruments and Some Results Of Observationsmentioning

confidence: 99%

Seafloor Geodetic Approaches to Subduction Thrust Earthquakes

Fujimoto¹

2014

Monogr. Environ. Earth Planets

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Observation systems and some observed results of seafloor geodesy are reviewed with a focus on the research activities of Japanese groups, especially those of Tohoku University. Seafloor acoustic ranging has been adopted as the simplest way to continuously monitor local crustal activities. The GPS-Acoustic (GPSA) method has been the most important for seafloor positioning. It seems that commercial technologies can be used to lessen the considerable differences in repeatability and spatio-temporal resolution of GPSA and land based GPS. Ocean bottom pressure sensors have been used to continuously monitor vertical crustal movements. Improvements in the resolution and long-term stability of pressure sensors will lead to monitoring slow slip events and interplate locking. Ocean bottom and underwater gravimeters have been developed for precise gravity mapping and monitoring mass change beneath the seafloor. The 2011 Tohoku-oki earthquake is an historical event demonstrating that seafloor geodetic observations are crucial to understanding the mechanism of giant earthquakes. Coseismic displacements detected through geodetic observations on the seafloor have indicated huge slips on the shallow part of the plate boundary. A slow slip event near the zone of the coseismic slip preceding the main event has been detected from slight pressure variations. This illustrates the importance of real-time monitoring with a cabled seafloor observatory, which is also a key to establishing a reliable early tsunami warning system.

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Existence of interplane earthquakes and neutral stress boundary between the upper and lower planes of the double seismic zone beneath Tohoku and Hokkaido, northeastern Japan

Cited by 77 publications

References 36 publications

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

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

Large intraslab earthquake (2011 April 7, M 7.1) after the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0): Coseismic fault model based on the dense GPS network data

Seafloor Geodetic Approaches to Subduction Thrust Earthquakes

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