Multi-channel seismic reflection profiling off Joban District, northeast Japan.
Cast your vote
You can rate an item by clicking the amount of stars they wish to award to this item.
When enough users have cast their vote on this item, the average rating will also be shown.
Your vote was cast
Thank you for your feedback
Thank you for your feedback
MetadataShow full item record
AbstractDuring November 1979, the Hydrographic Department of the Maritime Safety Agency, in cooperation with the Geological Survey of Japan, carried out a survey of sea bottom crustal structures along a straight line 274 km length across the Japan Trench off the Joban District in northeast Japan (Figure 1). The survey used a multi-channel seismic reflection profiling method on the Kaiyomaru, 990 tons JAPEX (Figure 2). The authors describe an outline of the structures from the seismic record sections obtained from the survey (Figures 3, 4, 5, 6, 7 and 8〕． The continental slope is formed with sedimentary layers (A, B, C, D and E), 1～3 km thick and its basement (F〕， which are presumably inferred to be the Quaternary to the Tertiary and the Cretaceous respectively, based on a comparison with investigations off the Sanriku District (Figure 9)． The basement is folded in 30～50 km wavelengths on a large scale, and is able to be traced from the continental shelf to the 6500 m deep bench. The sedimentary layers are gently folded with a characteristic change of folding axis in the locality such as a non-turnover type of the shelf break area, a turnover type of the deep sea terrace area, and a shift type of the trench slope area, accompanied by a synthetic fault, an antithetic fault, and a reverse fault, respectively. The outer trench slope which is formed with the upper layers (Ao, Bo), average 0. 7～1.1 km in thickness and a basement (Co〕, gently slanted to the trench axis, accompanied by some graben and horst like structures. Furthermore, a part of the upper layers and the basement trace from the trench axis to beneath the (inner) trench slope, a distance of 50 km with an average inclination of 5°, and 9 km deep under the sea bottom. Beneath the inner trench wall, an accretionary prism-like structure can be seen. A historical development of structures of the continental slope is presumably as follows : After sedimentation and subaerial erosion of the Cretaceous, it formed large scale foldings with 30～50 km wavelengths. Synclinal areas became sedimentary basins of the Paleogene and successively incurred a subaerial erosion. In the Neogene, a sedimentary basin extended on all over the continental slope area. The layer was deformed by a tectonic movement. A syncline beneath the lower deep sea terrace changed to an anticline axis, and the trench slope area warped down toward the trench axis. In the upper Neogene-Quaternary, a sedimentary basin was laid on the continental shelf and the deep sea terrace area, or subaerial erosions occurred in almost all anticlinal heights during this age.
JournalReport of Hydrographic and Oceanographic Researches