Recent Progress in Tectonic Geomorphology in Japan, with Special Reference to Active Fault and Related Tectonic Studies

抄録

Active fault and related tectonic studies in Japan are chronologically reviewed from the viewpoint of tectonic geomorphology. The future prospects are also described based on the trends of recent progress in active fault study and the surrounding social circumstances. Since the publication of Active Faults in Japan in 1980, the field in Japan has roughly been split into two domains: the reconstruction of detailed fault behavior in Holocene times; and the elucidation of the relationship between active faults and regional tectonics. The former describes various kinds of fault behavior through the application of the trench excavation method. Although the historical activity has been uncovered on many active faults, the surveys have become increasingly difficult due to the artificial modification of land. New proposed methods such as drilling, however, have not yet developed sufficiently to substitute for trenching. The latter domain discusses various topics related to the characteristics of long-term tectonic behavior from the viewpoint of landform evolution. Studies on the net slip-rate of thrust faults and the migration of thrust fronts have brought new knowledge and ideas to landform geomorphology and seismotectonic research. The morphotectonic and seismotectonic studies in offshore and onshore regions along the Nankai Trough have sufficiently explained the tectonic and landform evolution on the island arc scale in Southwest Japan. Based on present conditions, the author proposes the following directions which should promote progress in active fault study and to utilize the results for hazard mitigation in the future: (1) to distinguish the segmentation structure in the active fault system; (2) to establish seismotectonics models for various regions in Japan; and (3) reconsideration of the recurrence interval of large earthquakes.