Failure mechanism of a flow-like landslide triggered by the 2018 Western Shimane Earthquake
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Ran Li I Fawu Wang I Shuai Zhang
Failure mechanism of a flow-like landslide triggered by the 2018 Western Shimane Earthquake
Abstract The flow-like Kataragai landslide triggered by the 2018 Western Shimane Earthquake occurred in a gentle slope out of the area which suffered from the most intense ground motion. The geotechnical and hydrological conditions are considered as the primary factors for the landslide occurrence. It is confirmed through the field survey that the Kataragai landslide occurred in a refilled slope composed of medium sand with gravel, and several small ponds scattered on the refilled slope with perennial water. The existence of downslope seepage flow was validated by selfpotential tests and the seepage flows at the center of the crown near the pond are more noticeable. A weak layer with low dry density and fine-particle content was confirmed through hardness tests and penetration tests. The triaxial tests indicate that the antiliquefaction strengths of the soils in the Kataragai landslide are relatively low on the whole, while the weak layer is the lowest. The erosion of fine content in soil due to seepage flow is responsible for the formation of the weak layer. Based on the soil property and hydrologic condition, the initiation and motion mechanisms of the Kataragai landslide were discussed as well. Keywords 2018 Western Shimane Earthquake . Flow-like slide . Seepage . Liquefaction Introduction A MJMA 6.1 (Mw 5.7) earthquake with a focal depth of approximately 12 km struck Oda, Shimane, Japan, at 1:32 (JST) on 9 April 2018 (Japan Meteorological Agency 2018a; Geospatial Information Authority of Japan, GSI 2018). The epicenter of the 2018 Western Shimane Earthquake is located at 35.2° N, 132.6° E and the maximum seismic intensity is 5 on the Japan Meteorological Agency (JMA) scale (Japan Meteorological Agency 2018b). A PGA of 6.762 m/s2 was observed in a K-NET station (SMN006) approximately 8.0 km northwest to the epicenter (National Research Institute for Earth Science and Disaster Resilience (NIED) 2019). Only two landslides (the Kataragai landslide and the Shitsumi landslide) were triggered by the 2018 Western Shimane Earthquake (Fig. 1). The occurrence of coseismic landslides has been prevalently considered being closely related to the PGA, seismic intensity, topography, geological condition, and hydrological condition in previous studies (Liao and Lee 2000; Wang et al. 2002; Gorum et al. 2013; Xu and Xu 2014; Zhang et al. 2019). However, the flowlike Kataragai landslide occurred in a gentle slope approximately 14.7 km southwest to the epicenter and the Shitsumi landslide occurred in a steep slope beside a highway with an epicentral distance of approximately 8.7 km. As is illustrated in Fig. 2, both the Kataragai landslide and Shitsumi landslide are distributed out of the area which suffered from the most intense ground motion. The occurrence of the Kataragai landslide and the Shitsumi landslide seems to be influenced more by the geotechnical and hydrological conditions than seismic conditio
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