Multichannel seismic reflection survey was performed at southeast of the Izu Oshima in March, 1987. Based on the multichannel seismic reflection profile, we can iendify at least five units. Those are units A, B, C, D, and E. Units C and D are considered as trough filled sediments judging from their distribution and are correlated with the Shiozawa Formation (0.4-1.0 Ma B. P.) and the Neishi, Seto, and Hata Formation (1.4-2.0 Ma B. P.) of the Ashigara Group respectively. Many normal faults are developed in unit D and acoustic basement (the Shirahama Group), however scarcely in upper units. Unit D is stepped down toward the Sagami Trough by the faults with gradual increase in its thickness. The normal faults are closely related to formation of the present morphology of the Sagami Trough. Therefore, we interpret that unit D was deposited during formation of the Sagami Trough. Both units A and B are correlated with volcaniclastic sediments in the upper Pleistocene and the Holocene. On the western slope of the Sagami Trough, upper part of unit A is sliding down toward the Sagami Trough with a length of approx. 7 km. An instantaneous amplitude of the seismic profile indicates that the Habu Spur is composed of many igneous intrusions. The Habu Spur has a trend of NW-SE direction which is consistent with that of lateral volcanoes of the Izu Oshima. It is considered that the Habu Spur is the southeastern extension of lateral volcanoes of the Izu Oshima.
