THE 1995 KOBE EARTHQUAKE AND PROBLEMS OF EVALUATION OF ACTIVE FAULTS IN JAPAN

The Kobe earthquake (M 7.2) of January 17, 1995, which was the most da maging earthquake in recent Japanese history, made manifest the need f or reconsidering the method of evaluating active faults. An earthquake of this magnitude at this time was unexpected according to convention al evaluation, in which the potential magnitude of earthquakes at a ce rtain site is estimated by considering the greatest earthquake in the past 400 years and the length of the active fault. The following chara cteristics of this earthquake made it appear unlikely by conventional understanding: (1) the Kobe earthquake involved several neighboring fa ults, which had been previously been identified as separate fault syst ems: (2) the surface rupture of about 10 km length was much shorter th an the 50 km seismic faulting; (3) the interval of 400 years between t he Kobe and penultimate Keicho earthquake of 1596 AD (M 7.5), which ha s been revealed by historical documents and some excavations, is much shorter than the 2000 years estimated by calculating the average slip rate of displaced landforms. These shortcomings imply that active faul t evaluation with the traditional characteristic earthquake model whic h deals with each fault separately, is not adequate for an area like J apan where active faults swarm. New concepts such as the block rotatio n model (Kanaori, 1990; Late Mesozoic-Cenozoic strike-slip and block r otation in the inner belt of Southwest Japan. Tectonophysics, 177: 381 -399) considering the macroscopic tectonic framework for fault interac tions are needed. Furthermore, fault dynamics cannot be ignored; physi cal and temporal parameters associated with faulting, such as moment r elease rate, must be considered for realistic and precise evaluation.