Role of geological structure in the occurrence of earthquake-induced landslides, the case of the 2007 Mid-Niigata Offshore Earthquake, Japan

The second largest landslide occurred on a west-facing orthoclinal slope. A rotational rock slide, Unit A, was 80 m wide and 100 m long. During the excavation after the landslide, a high angle fault with a SW dip was identified behind the crushed zone. Based on field observation, the fault was considered to be a non-tectonic fault and created by gravitational movement. During the excavation, the crushed zone was identified on the cutting wall of the slope. These results revealed that the relatively larger rotational rock slides occurred because of the existence of the crushed zone due to older events that caused the slippage along a non-tectonic fault.