Evaluating the activity of Holocene faults in Japan

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The overall objectives of this study are to evaluate the activity of Holocene faults in Japan, and to provide basic quantitative data for understanding the tectonics of the Japan arc in recent geologic past.In 1995-1997, we carried out air-photo interpretation over representative fault zones in the Japan arc using high-resolution, large-scale aerial photos, in order to map precise geometry of and to extract deformation associated with Holocene faults. As a result of this work, we found many lines of new evidence for surface deformation on Holocene geomorphic surfaces, which provide us important data for segmentation and grouping problems of active faults. Part of this mapping work has been published as "Active Fault Map of Urban Area" Series from the Geographical Survey Institute in 1996.In order to determine the rate of net slip on a fault zone, information on subsurface geometry of the fault zone, as well as the rate of surface deformation, is necessary. On the basis of air-photo mapping, we carried out field researches of geomorphology, surface geology, drilling, reflection seismic profiling, and gravity survey for selected fault zones in 1996-1997. These integrated researches have revealed to be effective in evaluating the overall activity of faults in recent geologic past.