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

两年的海底地震地质研究成果从方法和战术上总结如下：由于日本群岛周围的大多数活动断裂与陆地上类似，位于海底海脊和盆地之间的边界上，如果有地震剖面测量的水面舰船资料，它们可以大致定位。然而，直接观测底部的活动断裂是相当困难的，因为较活跃的断裂由于其自身的地震活动，往往容易被湍流的底部流所埋藏。用于寻找海底活动断层的标志不是万能的，但却是有效的指示器是变色垫子，包括自生化学沉积物、细菌垫子和文蛤群落的田野。此外，还发现了新的碎屑带、地裂缝、切割现代沉积物的全新断裂带、断裂面上的新滑线等。t…北部震中地区的海底同震重震作用1993年，北海道西南部海域发生地震，这在世界上尚属首次。该报告包括：1)以松散泥层的自生角砾化为特征的“地震碎石”；2)由于斜坡失稳和/或滑坡而在陡峭山丘前的泥质平底上几乎不分布的“跳落碎石”，表示主震期间的强烈运动，并可通过潜水调查观察到。根据Kaiko和Kaiko-South kai项目期间记录的静态照片和视频分析，利用断层滑移感、碎屑岩墙和节理等构造指标，对南开海槽东部的地震构造进行了研究。内外韧性斜坡的构造应力方向不同，间接指示了阿穆里亚板块(Enshu-nada深海阶地)的东移和菲律宾海板块(泽尼苏海脊)的北移。相反，在日本海东部海域没有发现这种应力分带，这可能是由于阿穆尔板块和鄂霍次克板块之间的板块边界太不成熟所致。较少

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