<国立科博専報>Seismic Profiler による三陸沖の堆積層の研究

概要

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A seismic profiler survey was undertaken off the Sanriku coast, across the rather wide continental slope with a width 130km and a general dip about one degree. The basement of the major part of the slope is covered with two layers of the younger sediments. The lower transparent layer of the two was deformed concordantly with the rugged surface of the basement, probably due to the same crustal movement, and it is uniform in thickness, while the upper opaque one seems to be a sediment covering the undulated transparent layer, perhaps due to turbidity current. Referring to the data of the seimic refraction survey made by the writers previously (LUDWIG et al., 1966), it may be supposed that the transparent layer has an acoustic velocity of 1.7km/sec, a value corresponding to that of the upper Neogene to Pleistocene sediments, and that the basement possesses the value of 2.5km/sec. At the lower end of the above-mentioned slope at a depth about 2000m, the basement is exposed forming an eroded terrace-like topography with a rather horizontal, though slightly rugged, surface. From the depth below the terrace, i.e., at the points S_1 and S_2 of Fig. 1,IIJIMA and KAGAMI (1961) obtained many pebbles, some of which were regarded to be of the late Miocene or early Pliocene. These rock fragments of the Neogene, therefore, may have been brought from the terrace, not from a distant source, probably by turbidity current.
国立科学博物館の論文
1968-03-30