ABSTRACT:

The aim of this paper is to estimate the earthquake hazard to human life using the simulated 30-year probabilities of earthquake occurrence from the main active fault systems in the Japanese archipelago. Errors in estimation are evaluated at the same time. The number of earthquake occurrences from the active fault systems over 30 years is estimated in the present paper to be about 3. The total expected superficial dimension of the potential disaster area is estimated probabilistically at about 2,500~3,500 (km2), and the total expected population affected at about 800,000~1,800,000. These represents of the superficial dimensions or the populations of the areas that may affected by an earthquake motion of PGA2::4.0m/sec2 evaluated using equations by Fukushima & Tanaka, and Hayashi & Abe. These figures would be larger than the actual amount, due to several factors use in the equations. The present paper also shows that prioritising trenching investigations around highly densely populated areas is effective in mitigating the effects of earthquakes. In a case study ofthe Gofukuji fault system, the expected population due to a future earthquake is estimated to be the extremely large figure of 48,871~132,650.

INTRODUCTION

The aim of the present paper is to assess hazard to human life due to large intraplate earthquakes caused by seismogenic active fault systems distributed over the Japanese archipelago. Simulated 30-year probabilities and potential disaster populations are used for this assessment. Here the 30-year probabilities are of earthquakes occurring within a 30-year period from the present time, and the potential disaster populations are of those distributed around the major active fault systems who will be affected by the earthquake motions. A Subcommittee for Long-term Evaluation of Earthquake Research Committee of the Headquarters for Earthquake Research Promotion has determined the periodicity of earthquake occurrences from each active fault system.

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