Detailed Geomorphological and Geological Investigations for the Major Active Faults Carried out by Trenching

阿特拉断裂是一个以左旋为主的主断裂系统，已被几个沟研究过。通过对这些结果的比较，明确了主断层在大地震发生的整个轨迹上同时发生错位，因为每个沟具有相似的重复间隔。由于该断层断层形态较为复杂，采用1:25 000比例尺的照片解译绘制了详细的断层迹线和断层分类图。对日本陆地上主要活动断层的挖掘研究主要是为了揭示至少在过去几千年里每次断层事件的年龄和真正的复发间隔。最后一次史前事件的精确数据对于评估未来的地震危险性尤为重要。因此，碳14测年和考古方法被用来确定地层和事件。通过这些调查，明确了主要活动断裂，特别是Atotsugawa断裂、Itoigawa-Shizuoka构造线（中部）、中间构造线冈村断裂和Atera断裂的破裂事件、复发间隔、断裂地下结构和断裂行为等。详细的描述和信息已发表，每篇论文在参考文献中列出。东京大学出版社出版了一本名为《九州的活动构造》的综合性书籍。冈田是这本书的主要作者。本书旨在以1:50 000比例尺的薄片图的形式呈现活动构造（活动断层、褶皱、区域隆起和下沉等）、地貌面分类、滑坡分布和火山元素等数据。特别是详细介绍了九州地区的活动断层，阐明了活动断层的纬向排列、区域背景及其与地震的关系。

The Atera fault forms a master fault system with predominantly left-lateral component of displacement and has been studied by several trenchings. Comparing these results it has been clarified that the main fault would simultaneously dislocate through the whole trace with large earthquakes, as each trench has the similar recurrence interval. As this fault has rather complex fault pattern, detailed traces and classification of faults were mapped by photo-interpretation on a scale of 1:25,000.The excavation study for major active faults on land in Japan has been aimed principally at revealing ages of each event of faulting and real recurrence intervals during, at least, the last several thousand years. The precise data of the last prehistoric event are particularly important for evaluating future seismic hazard. Therefore, carbon-14 datings and archaeological methods were used to determine the strata and events. From these investigations, rupture event, recurrence interval, subsurface structure of fault and behaviors of faulting and so on were clarified for the major active faults, especially Atotsugawa fault, Itoigawa-Shizuoka Tectonic Line ( central part), Median Tectonic Line Okamura fault) and Atera fault. Detailed description and information were published with each papers listed on references below.A comprehensive book entitled with "Active Tectonics in Kyushu" was published from the University of Tokyo Press. Okada is the chief author in this. This book aims to present such data as active tectonics(active fault, folding, regional uplift and subsidence etc.), classification of the geonorphological surfaces, distribution of the landslide, and volcanic elements in the form of sheet maps on the scale of 1:50,000. Especially, this book provides detailed informations on active faults in Kyushu and clarified the zonal arrangements, regional setting and relationship to the earthquakes of active faults.