DESCRIPTION OF SUBMARINE ACTIVE FAULTS AROUND JAPANESE ISLANDS-A BASIC INVESTIGATION FOR SUBMERSIBLE SEISMOGEOLOGY-

本文从方法和战术上总结了两年来的海底地震地质研究成果：日本列岛周围的活动断层大多与陆地上的活动断层一样，位于海脊与海盆的沿着边界上，因此，如果有地震剖面测量的水面舰船资料，就可以大致确定这些活动断层的位置。然而，直接观测海底的活动断层是相当困难的，因为活动性较强的断层由于其自身的地震活动而容易被动荡的底流所掩埋。在寻找海底活断层时，变色席（包括自生化学沉积物、细菌席和蛤蚌群）不是万能的，但却是有效的标志。此外，还可见到新的岩屑带、地裂缝、切割现代沉积物的全新断层陡坎、断层面上的新滑线等。 ...更多信息 1993年北海道西南近海地震是世界上首次报道的地震。报告包括新的鉴定：1）以松散泥层的自生角砾化为特征的“震砾”; 2）由于斜坡破坏和/或滑坡，在陡坎前的泥质平底上几乎不分布的“跳落砾”。这表明了主震期间的强烈运动，并通过潜水调查得到了明显的观察。在对KAIKO和KAIKO-NANKAI计划期间记录的静态照片和视频影片进行摄影分析的基础上，使用断层滑动方向、碎屑岩脉和节理等结构指标进行了调查。构造应力方向的差异，在内部和外部的坚韧斜坡，间接指示阿穆尔板块（恩舒-那达深海阶地）的东部运动和菲律宾海板块（Zenisu海岭）的北移。而日本海东部海域沿着没有发现这种应力分带，这可能是由于阿穆尔板块与鄂霍次克板块之间的板块边界太不成熟的缘故。少

Results of the two years project for submarine seismogeology are summarized methodologically and tactically as follows :Since most active faults surrounding JapaneseIslands locate along boundaries between submarine ridges and basins similarly as on land, they can be roughly located if surface ship data of seismic profiling surveys are available. Direct observation of active faults on the bottom, however, is rather difficult because the more active faults tends to be buried easily by turbulent bottom current due to their own seismic activities. Not almighty but effective indicators used as markers in searching for submarine active faults are altered-color mats, including authigenic chemical deposits, bacterial mats, and fields of clam colonies. In addition, zones of fresh debris, ground fissures, brand-new fault scarplets which cut the recent sediments, fresh slickenlines on fault planes, and so on, are also available.Submarine co-seismic diastrophism in the northern epicenter area of t … More he 1993 South-western off Hokkaido earthquake was reported for the first time in the world. The report includes the new identifications of 1) "quake-rubble" characterized as autochtonous brecciation of unconsolidated mud layr and 2) "jump-fall rubble" scarcely distributed on the muddy flat-floor in front of steep scarps due to slope failure and/or landslide, which denote the strong motions during the main-shock and were visibly observed by submersible investigations.Seismotectonics along the eastern Nankai Trough werere-investigated on the basis of photographic analyzes of still-photos and video films recorded during the KAIKO and KAIKO-NANKAI programs, using structural indicators such as slip sense of fault, clastic dikes and joints. Tectonic stress orientation differs among the inner and outer tough slopes, indirectly indicating eastern motion of the Amurian plate (Enshu-nada deepsea terrace) and northward motion of the Philippine Sea plate (Zenisu Ridge). On the contrary, no such kind of stress zonation is found along the eastern maegin of Japan Sea, possibly because the plate boundary between the Amur and the Okhotsk plates are too immature. Less