Distribution of Landslides Triggered by the 1995 Hyogo-ken Nanbu Earthquake and Long Runout Mechanism of the Takarazuka Golf Course Landslide

Abstract

The 1995 Hyogo-ken Nanbu earthquake caused not only casualties and damage to buildings and civil structures but also many landslides. Most of the landslides were triggered or reactivated in the northeastern part of the Rokko Mountains, Nishinomiya and Takarazuka Cities, and the northern tip of Awaji Island. Based on the analysis of aerial photographs coupled with field surveys, 674 landslides were mapped within an area of about 700 km2. The observed landslides were mainly rock slides, rock falls, and rock/debris avalanches. Debris slides, complex slides, and slumps were also found. A few debris slides showed low apparent friction angle during motion with long runout distance. The investigations of landslide typology and distribution show that, based on the relationship between landslide frequency and distances from the assumed fault rupture zone, an attenuation trend can be observed which shows a significant decrease within 3 km, while the maximum recorded distance was 10 km. While focused on the long runout mechanism in the Takarazuka golf course landslide, an undrained loading ring shear test on saturated golf course soil was carried out and succeeded to reproduce the low apparent friction angle mobilized in the landslide.