Tectonic Geomorphological Active Fault Studies in Japan after 1980

Abstract

Tectonic geomorphology has played important roles in active fault studies in Japan. Following large historical earthquakes, the concept of active fault was formulated and detailed information has rapidly accumulated. This paper reviews the progress of active fault studies in Japan since the 1980s. The period 1980 to 1994 can be regarded as the matured period of active fault studies during seismic calm. The studies conducted during this period are categorized into the following: 1) excavation studies of active faults, 2) analytical studies of tectonic landform evolution based on dislocation models, 3) chronological studies supported by the development of age determination techniques, and 4) studies quantifying the rate of crustal deformation. In 1995, the Great Kobe Earthquake occurred. The earthquake triggered a seismically active period in Japan, and the active fault has become an important issue in disaster mitigation. The research in the decade after 1995 can be summarized as follows: 1) intensive investigations of active faults, 2) detailed large-scale mapping, 3) seismic reflection profiling, 4) long-term forecasts of earthquakes, 5) careful study of flexural deformation, and 6) overseas research on large destructive earthquakes. Then, the period since 2005 has witnessed the rediscovery of active faults, with research considering 1) the relations between the large earthquakes which often occurred in this period and their seismogenic active faults, 2) precise distribution of active faults, 3) the relations between active tectonics and geodetical movement, 4) the relations between interplate earthquakes and submarine active faults, and 5) the difficult problems of prevention against infrequent disasters like the 2011 Great East Japan Earthquake. Additionally, since around 2006, some nuclear power plants have faced problems associated with active faults because some active faults had been overlooked or ignored in the seismic design of these plants. Active fault research now bears greater social responsibility.