[H-DS07] Landslides and related phenomena

[HDS07-18] On the initiation and movement mechanisms of Zhongchuan landslide triggered by the 2023 Jishishan M6.2 Earthquake, China

*Gaoyuan Wang¹, Xuanmei FAN¹, Fanyu Zhang², Ruihua Hao², Gonghui Wang³ (1.State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, 2.School of Civil Engineering and Mechanics, Lanzhou University, 3.Disaster Prevention Research Institute, Kyoto University)

Keywords:Fluidized landslide, Earthquake, Liquefaction, Irrigation, Rapid movement, Long runout

At 23:59 on December 18, 2023, a destructive Ms 6.2 earthquake struck Jishishan County, Gansu Province, China. The earthquake triggered a large-scale loess landslide in Zhongchuan District, Qinghai Province, approximately 20 km from the epicenter. The landslide originated on a loess terrace used for farmland, where the displaced material fluidized and traveled down a narrow valley, devastating villages downslope before depositing in a residential area. With a travel distance of about 3 km and an elevation drop of approximately 80 m, the landslide exhibited an exceptionally low apparent friction coefficient (~0.0026). It destroyed over 50 houses and caused more than 20 fatalities. Notably, few landslides were triggered by this earthquake, yet this particular event displayed extreme mobility, underscoring the need to understand its initiation and movement mechanisms. To investigate this, we conducted geological and electrical resistivity tomography (ERT) surveys to assess the subsurface structure of the landslide area. Additionally, field double-ring infiltration tests and laboratory experiments (including direct shear, static triaxial, dynamic triaxial, and ring shear tests) were performed on soil samples taken from the landslide source area to evaluate their shear behavior under various conditions. Based on these results, we discussed the effect of earthquake and irrigation on the initiation and movement of this catastrophic landslide. The findings from both field and laboratory analyses provide critical insights into the triggering and movement processes of this highly mobile landslide.