Lethality level analysis of secondary landslides based on field survey data: a case study of Luding earthquake

Through on-site investigation, the number, locations, and causes of death in the Luding earthquake were obtained. Based on an analysis of the causes of death, 44.1% of the deaths were caused by building collapse, and 54.8% were caused by earthquake-induced geological effects. Therefore, it is particularly important to conduct research on targeted methods for assessing casualties for emergency rescue work after earthquakes. First, this article analyzes the number of deaths as a result of different earthquake intensities and building types and, combined with data from 81 on-site survey points (lethality levels and quantity and ratios of different types of buildings), obtains the regional lethality levels for different intensities and administrative units in the study area (intensity VIII and IX areas). Second, based on on-site investigation results of points at which secondary geological effects (landslides and rolling stones) occurred, and by combining parameters, such as the slope, slope direction, slope curvature, and distance from the fault, this study obtains the risk level of earthquake-induced landslides. On this basis, a coupling analysis is conducted on the seismic landslide risk level and lethality level. The results show a positive correlation between the risk level and the lethality level; the higher the risk level, the higher the corresponding lethality level is, but this relationship is not absolute. The Pearson’s correlation coefficient for the fitting results is 0.70828, the coefficient of determination R 2 is 0.50102, and the mean squared (MS) is 0.029. The results of the sensitivity analysis of the two levels show values that are above the average level, with the prediction accuracy of the landslide risk level and lethality level being 0.708 and 0.609, respectively. The fitting results show average values at a moderate level; by constructing a fitting relationship between the landslide risk level and lethality level, the relationship can provide ideas and feasibility for constructing a lethality matrix for secondary geological disasters during earthquakes. Furthermore, it is possible to quickly evaluate the number of deaths due to secondary geological effects of the earthquake.