A probabilistic method to assess the regional susceptibility of landslides induced by earthquake in Kitakyushu city, Japan

Here a probabilistic method for assessing the regional susceptibility of landslides induced by earthquake events was developed. This probabilistic method, furthermore, was applied into the Kitakyushu city of Japan, which suffered the landslide disasters induced both by rainfall and earthquake seriously. Failure probability of earthquake-induced landslides based on Monte Carlo simulation (minimizing the uncertainty of slope parameters) and a developedmethod after Newmark stability analysis (estimating factors of safety) was calculated. Meanwhile, regional susceptibility maps of earthquake-induced landslides in Kitakyushu city were produced by using the geographical information system (GIS) with different peak ground accelerations (PGAs) and seismic occurrence periods at both conditions of m=0 and m=1 (m, so-called water factor which means a ratio of groundwater level to thickness of sliding layer). Analysis results of failure probability disclose that the influence factors of slope angle, PGA and m on failure probability (stability) of earthquake-induced landslides would have to be considered carefully in the Kitakyushu city. The PGA exerts distinctly different influence on the stability of landslides varying with soil type and m. According to a new geology map of Kitakyushu city, the maximum average value of slope angles is less than 50 degree. A softer slope tends to suffer a greater increment of failure probability impacted by the PGA in the case of a lower angle than a higher one, within the range of slope angles, 0∼50 degree. This becomes more visible while the PGA increases. On the susceptibility maps, it is evident that the districts of Kokura Minami, Moji, Kokura Kita, Yahata Higashi and Yahata Nishi in Kitakyushu city would suffer the disaster of landslide severely. In the lower cases of PGA, the Southwest of Kokura Minami, the borders between Moji and Kokura Kita and the borders between Yahata Higashi and Yahata Nishi are the major areas impacted by extremely serious hazard of earthquake-induced landslides. As PGA, seismic occurrence period or/and m increases, critical disaster of landslide has an extensive area, covering Wakamatsu. Nevertheless, Tobata, the only one of fortunate district throughout Kitakyushu city, is in safety all the time.