大地震の発生直後には，被害の概要がわからない場 合が多い。このような場合，災害対策の初動段階では， 実際の被害情報ではな〈ても，ある程度の根拠を持っ た被害の予想（例えば，定性的な根拠はあるが，十分 検証されていない方法による予想）であれば，有用な情報となる。%Rokko formula is a discriminant function for risk assessment of slope failures by earthquake. There are three problems to apply the formula for real time anticipation : too narrow target range of PGA (peak ground acceleration), lack of PGA data, and too long calculation time. We developed modified Rokko formula, estimation method of PGA from JMA (Japan Meteorological Agency) seismic intensity scale, and calculation method using precomputed histogram of real-time-independent part. We applied the methods to past earthquakes using shake maps (estimated seismic intensity distribution data) by JMA, and compared the results with slope failure positions by air photo interpretation. The results were appropriate in the interpretation area except narrow steep-slope-strips, but the system sometimes anticipated higher risk at the outside of the interpretation area. The difference was mainly caused by lack of seismometer near the epicenter.
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