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

Atera断层形成了一个以左侧位移为主的主断层系统，并已通过几次开挖进行了研究。对比这些结果，可以清楚地看出，由于每个海沟有相似的复发间隔，主断层在大地震时会同时在整个道上错动。由于该断层具有相当复杂的断层形态，因此用1：25000比例尺的摄影解译绘制了详细的断层踪迹和断层分类图。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最近几千年来每一次断层事件的年龄和真实的重复间隔。最后一次史前事件的准确数据对于评估未来的地震危险性尤为重要。因此，使用碳14测年和考古方法来确定地层和事件。通过这些研究，明确了主要活动断裂的破裂事件、复发间隔、断层的地下结构和断裂行为等，特别是Aotsugawa断裂、Itoigawa-Shizuoka构造线(中部)、中间构造线(冈村断裂)和Atera断裂。发表了详细的描述和信息，并在下面的参考文献中列出了每一篇论文。东京大学出版社出版了一本名为《九州的活动构造》的综合书籍。冈田是这篇文章的主要作者。本书旨在将活动构造(活动断裂、褶皱、区域隆起和沉陷等)、地貌面分类、滑坡分布和火山元素等数据以1：50,000比例尺的电子地图的形式呈现出来。特别是该书提供了关于九州活动断裂的详细信息，阐明了活动断裂的带状布置、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.