Three-dimensional structure of so-called double seismic zone of deep earthquakes in Northeast Japan.(<Special issue>Crustal structure and geotectonic history, Northeast Japan Arc)

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  • 東北日本のいわゆる二重深発地震帯の3次元構造(<特集>東北日本の島弧地殻構造と地質構造発達史)
  • 東北日本のいわゆる二重深発地震帯の3次元構造
  • トウホク ニホン ノ イワユル ニジュウ シンパツ ジシンタイ ノ 3ジゲン コウゾウ

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Abstract

Focal depth of deep earthquakes in northeastern Japan has become progressively deeper towards the west from the Japan Trench. The deep earthquakes believed that have a two-layer structure, and they are referred to as double seismic zone. The authors, intended for deep earthquakes of magnitude greater than 2.0 that occurred between 1983 and 2009, drew iso-depth contours of deep earthquakes. We have examined the correlation between the shape of virtual surface of hypocenter distribution and topography and geology. As a result, it was revealed that the distribution of hypocenter group to form double seismic zone have not been divided into two consecutive upper and lower layers, and distribution of earthquakes in the upper and lower surfaces of undulating virtual surface of hypocenter distribution are overlapping in the cross-section. When projected onto the surface of the two virtual surfaces of hypocenter distribution boundaries, its location is well consistent with the boundaries of the terrain unit, such as Yokote Basin and Ohu Mountains. This position is also the location of active faults. The slope of the surface where there is a sudden change of the virtual surface of hypocenter distribution would amount to the terrain where there is a sudden change, and suggests that the phenomenon of deep underground is affecting up to the surface.

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