Tectonic foliations and the distribution of landslides in the southern Central Range, Taiwan

Geometry of planner geological structures can interact with topographic slope and cause different types of slope failure (e.g. wedge failure, dip slope failure, and toppling etc.). This study focus on how the tectonic foliation influences the landslide pattern in the southern Central Range of Taiwan. The tectonic foliations in this area range from pencil cleavage to schistosity depending on the increasing of metamorphic grade, and different foliations have different influences on the landslide behaviors. To describe the relation between foliation and topographic slope, we create the θD value as the angle between the foliation dip direction azimuth and the topographic downslope direction azimuth at a given location. The location of landslides in the area with pencil cleavage has no preferential θD value, and it suggests the landslide distribution has no correlation with foliation. The location of landslides in the area with well-developed slaty cleavage is mostly in the lower θD value, which suggests the landslides are more likely located in the area where the foliation dip direction is parallel to the topographic downslope direction. The location of landslide in the area with schistosity is mostly in the high θD value area, which suggests the landslides are more likely located in the area where the foliation dip direction is opposite to the topographic downslope direction.