Multi-channel seismic reflection survey in the Nankai, Suruga and Sagami Troughs.

Abstract

In 1980 and 1981, nine Iines of multi-channel seismic reflection survey were carried out by the Hydrographic Department of Japan, in the Nankai, Suruga and Sagami Troughs bordering the northern subducting margin of the Philippine Sea Plate. Data were obtained by R/V Kaiyo-Maru of the Japan Petroleum Exploration Co., and processed in terms of the following methods; deconvolution, velocity analysis, 24 fold stacking, time migration, and depth conversion. Subduction of oceanic crust of the Philippine Sea Plate beneath the Japanese Islands is clearly recognized on the migrated depth sections. The subducting oceanic crust is pursued for at least 30 km landward from the axis of the Nankai Trough with the inclination of 3°- 5°. On the landward slope of the Nankai Trough, distinctly imbricated sediment bodies with many thrust faults were found. In the Suruga Trough, the basement forming the Izu Peninsula is traced beneath the Trough and western slope of it for about 8 km with an inclination of 7°-23°. In the Sagami Trough the basement forming the Izu Peninsula is recognized beneath the Trough to the Misaki Knoll located on the eastern slope of the Trough, with an inclination of about 10°. Key word: Multi channel seismic reflection survey. Nankai Trough; Suruga Trough; Sagami Trough; Subduction of the ocean crust.