1975年3月坂出沖爆破地震動観測による四国の地殻構造

抄録

The crustal structure of Shikoku, Japan was studied by seismic refraction experiments which were carried out in March 1975. Thirteen temporary stations were aligned to the SW direction from off Sakaide to Cape Ashizuri, Shikoku. All of the stations were equipped with magnetic tape recording systems.
Two kinds of refracted waves with the apparent velocity of 6.05km/s and 7.8km/s were observed as first arrivals, although the seismograms were not of good quality. Certain secondary phases can be interpreted as refraction from the layer of 6.6km/s velocity.
Because of small number of data and of lack of reversed profile, only a rough picture on the crustal structure can be discussed in this paper. The superficial layer with a velocity of 5.5km/s becomes thin toward the southwest in Shikoku. This layer shows an abrupt change of its thickness at about 25km south of the Median Tectonic Line. The upper crustal structure with a velocity of 6.0km/s has an average thickness of about 20km. The velocity of the lower crust is assumed as 6.6km/s. The derived crustal structure is concordant with the structure of the eastern part of Shikoku derived from the Miboro and the Toyama explosions.