降雨確率と表層崩壊確率に関するシミュレーションによる検討(2) : 長期的にみた場合の崩壊に効果的な降雨の再現期間

概要

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Frorm a geomorphological perspective, heavy rainfalls with long return periods are not necessarily effective in producing shallow landslides because they seldom occur. This issue relates to magnitude-frequency issues in geomorphology. The effective return period of rainfall for long-term analyses of shallow landsliding was then theoretically estimated using a stochastic landslide model The probability density function P, of return periods N for rainfall events that generate landslides can be expressed as P_r=S(N)/N^2, where S(N) is the probability that rainstorms with a return period N trigger landslides. N_<max>, corresponding to the maximum of P_r, can be considered as the most effective for landsliding. For transport-limited conditions, P_r=1/N^2 when N>N_0, and P_r=0 when N<N_0, where N_0 is the critical return period of rainfall and constant. Therefore N_<max> is equal to N_0. For weathering-limited conditions the values of P_r were calculated in a field site using a DEM. It was found that the average values of the probability density P_r is influenced by the average recurrence interval of shallow landsliding and slope angle. It was also found that rainfall events with return periods < 500 and < 1000 years trigger about 50 and 65 % of the total number of landslides over the long term, respectively.
日本地形学連合の論文
2003-04-25