四国東部・中国地域における深部地殻構造探査

Abstract

In the summer of 1999, we conducted a highly dense, onshore-offshore integrated seismic experiment in the eastern part of Shikoku Island and the Nankai Trough off Shikoku Island, SW Japan. On shore, 93 land seismic stations were deployed on a 165-km-long line in the north-south direction. The intervals of the stations were about 1-2 km. Three explosives were fired as controlled seismic sources. Off shore, an air-gun array was fired at intervals of 200 m. Seismic signals both from land explosives and the air-gun array were recorded by the land seismic stations. We obtained high signal-to-noise ratio data along the entire length of the land profile. Very prominent late arrivals, probably reflected waves from the lower crust or the upper mantle, can be recognized on the record sections. An outline of this experiment is given in this paper, and a detailed analysis showing a structure model from the upper crust to the upper mantle beneath the eastern Shikoku Island will be published in a separate paper