A seismic risk evaluation method of old landslides and a prediction system on their collapse during an earthquake are developed. The seismic risk of each landslide is indexed by the critical acceleration which triggers the collapse and the factor of safety under gravity loading. Both values are calculated with the seismic slope stability analysis. The judgment of the collapse is based on the comparison between the critical acceleration and the estimated acceleration obtained from the hypocenter information and the attenuation relation for peak ground acceleration. The method is applied to the old landslides in the Hachimantai volcanic area, northeast Japan, shown on the landslide distribution map (scale1: 50, 000; NIED, 1984) , and the following examples are demonstrated: 1) the map of critical acceleration distribution, and2) the map of collapsed landslide distribution under an assumed earthquake.
The evaluation of the shear wave velocity distribution in the road embankment is necessary for the rational seismic assessment. However, the evaluation of shear wave velocity is usually difficult. In this study, the evaluation method of the shear wave velocity distribution in the road embankment using the microtremor measurement is proposed. First, the transfer functions of a high embankment in the Noto Toll Road were evaluated based on array measurements of microtremor at the toe, banquettes and shoulder. Next, the shear wave velocity profile of the high embankment was calibrated so that the transfer functions in the elastic FEM analysis agree with the observation. Finally, we confirm that a seismic response analysis using the estimated shear wave velocity is consistent with the actual damage results in the 2007 Noto Hanto Earthquake.
Recently, large-sized landslides causing a river blockage due to high magnitude earthquake or torrential rainfall occur and form a number of landslide dams. The water blocked by the dam may provoke floods which spread out the down stream area, causing damages to human activities and communication lines. The establishment of prediction method of breaching landslide dam is very important to prevent these disasters. Therefore, we examined the prediction method of breaching landslide dam utilizing by pattern classification analysis based on the fuzzy if-then rules using of data of the past landslide dams. In this analysis, new two indexes, where are designated as the ratio of landslide dam length/height (SFI) and the ratio of reservoir volume/catchment area (CAI) , are introduced for the prediction of breaching landslide dam. The result that improved of the precision of more than 10% of prediction accuracy is obtained. In addition, the influence degrees to the breaching landslide dam by the attribute factor are clarified from the fuzzy if-then rules obtained from the analysis.
Both earthquake ground motion and pore water pressure observations in valley fill were conducted in the southwestern Tokyo region from 2005 to 2011. The Nakane observatory is situated on the Musashino terrace. The Todoroki observatory about 2km distance from the Nakane is settled on the valley fill of 4meters depth and on the alluvial sediments of 6meters continued from the Pleistocene terrace. The difference in the earthquake ground motion between records on the both observatories varied with earthquakes. Earthquake response analysis by FLUSH using cyclic undrained triaxial test results on the undisturbed soil samples revealed that the amplification of the maximum ground acceleration (PGA) on the valley fill were controlled by the surficial ground structure and the characteristics of earthquakes. The non-linear response of excess pore water pressure in valley fill was observed during the strong earthquake such as the 2005 Chibaken-hokuseibu earthquake. These basic information will be valuable for discussing on prediction of valley fills type landslides induced by strong seismic motion in urban region.