日本の地殻構造

概要

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A model of the crustal structure of Honshu, Japan, deduced from the data obtained by the Research Group for Explosion Seismology is as follows : 1) The velocity of the shallowest layer is 5.5 to 5.8 km/sec and its thickness is less than several km. In some localities this layer does not exist and a layer with the velocity 6.1 to 6.3 km/sec is found just below surface layers. 2) The depth of the Moho discontinuity is about 20 km in north-eastern area, about 25 km in Kanto, and about 35 km in the central mountainous area. These values are deduced under the assumption that the crust is mostly composed of the material with the velocity of 6.1 to 6.3 km/sec. 3) The velocity of P wave below Moho discontinuity is slower than 8 km/sec. 4) According to the results obtained in the recent observations in the central and Kinki areas, a layer of about 6.6 to 6.7 km/sec exists below the layer of 6.1 to 6.3 km/sec. The part of the crust between this layer of 6.6 to 6.7 km/sec and the Moho discontinuity may have the velocity bigger than 7 km. 5) If we assume that a “hidden layer” of 6.6 to 6.7 km/sec exists in the areas described in (3), the calculated depth of Moho is about 10 to 20 percent deeper than the depth given in (3). 6) The “discontinuities” in the crust might not be so sharp as Moho discontinuity.
社団法人東京地学協会の論文