Crustal structure in a profile off the pacific coast of Northeastern Japan by the refraction method with ocean bottom seismometers.

Abstract

In October, 1978, the crust and upper mantle structure between the northeastern Honshu and the Japan trench was studied in a profile almost parallel to the trench axis by the refraction method with four ocean bottom seismometers. Sixteen explosions of dynamite in total were carried out for four ocean bottom seismometers with a spacing of about 90km. Only the northern two of which could be retrieved. The results show that the thickness of the crust is about 25km except for water and almost the same as that beneath Honshu, that the layer with a velocity of about 6.0km/sec is fairly thin near the Pacific coast and becomes thicker beneath the present profile, and that the Pn velocity in the present profile is 8.1km/sec and agrees with that in the adjacent areas. These features of the structure are of basic importance for studying tectonics of the island arc-trench system.