A review for the numerical methods to simulate natural-slope landslides, serving to discuss and synthesize key findings on this subject, is reported. The past works on the subject can be classified into the two categories such that（1）researches to understand and describe the landslide mechanisms and（2）researches to simulate the process of motion of a landslide mass. A state of the art review corresponding to each category will be demonstrated and it may offer new perspectives on the issue or point out an area in need of further research.
Using Synthetic Aperture Radar（SAR）, the previous study revealed 2007 Noto Hanto earthquake（M6.9）-induced landslide that slightly moved east. The landslide covers 1.5 km by 0.7 km and lies on anti-dipping gentle hilly slope, and cracks and small landslide were found on the edge of and inside the initial landslide area. In the area we performed boring survey, observed outcrop, and measured electric resistivity on the slope, pH and electric conductivity at springs and streams. Boring core and measurement result of electric resistivity did not show existence of clear slip surface ; however, measurement result of pH suggested the location difference between inner and outer are of the landslide, more specifically, existence of lower edge of the landslide area at 76 % correct discrimination ratio. These results infer that landslide blocks without clear slip surface moved east together at subtle deformation. And result of this study inferred characteristics of earthquake-induced landslide in the study area.
We observed time sequential changes of slopes prone to deep-seated landslides using aerial photographs and satellite images covering the last 60 years in the middle reach of the Ooigawa River Basin, in central Japan. We detected five deep-seated landslides that had shown significant expansion over the last 60 years（since 1947）, and examined their topographic features. In many cases, preceding small collapses were recognized on the foot of the bulging slope and otherwise, landslides expanded toward the upslope or laterally. The Houkinagi Landslide, the largest in this area, has shown a high expansion rate and significant mass creep over the past century, including a tension crack opening at a rate of around 10cm/year, found behind the main scarp. These phenomena found in deep-seated landslides indicate that precedent landslides at the foot of bulging slope will be useful premonitory features if accompanied with significant mass creep behind them.