Izu-Oshima volcano erupted on Nov. 15, 1986, 12 years since the last eruption in 1974. It is an important subject to determine the volcanic structure for a future eruption prediction. The shallow seismic profiles in the western and the central part of the island have been studied, but the profile in the eastern part of the island has not yet been determined.
In March 1987, a seismic experiment was carried out to determine the structure of the island and its periphery. In this paper, we derive and discuss the shallow seismic profile along the east coast of Izu-Oshima island with the refraction data generated by a large volume air-gun in the sea around the island. The air-gun was blasted along a line circling round the island. We presents the results obtained by analyzing the two series of blasting carried out off Okata-harbor, the north of the island, and off Habu-harbor, the south of it. The results derived from other blasts will be shown in following papers.
The derived seismic profile shows that the thickness of a surface layer in the northern area is thinner than that in the southern area and a slightly concave-like structure is locating in the middle of the profile.