Probabilistic Seismic Landslide Hazard Zonation Method And Its Application

Earthquake is one of the important triggering factors of landslides. Studies show that more than 4.0 magnitude earthquakes can trigger landslides, and medium and strong earthquakes can induce a massive landslide disaster, causing numerous casualties and property losses. In extreme situations, the losses from landslides damage induced by a gigantic earthquake could be more severe than the damage caused by earthquake. China locates between the two largest seismic belts, i.e. the circum-Pacific seismic belt and the Eurasian seismic zone. As a matter of fact, it is characterized by rugged topographies, frequent earthquakes, and thus notable seismically induced landslide hazards. With its rapid economic development, resource development and utilization, economic development strategy to the transfer of the western mountains, there will be more and more urban planning, site selection for railways, highways, dams and so on in the mountain area, suffering severe earthquake landslide risk. Prediction and zonation of seismic landslide hazard are urgently needed to avoid and mitigate their damage.Eearthquakes cannot be predicted at the present level of science. In the evaluation of earthquake-induced landslide at regional scale, such uncertainty should be considered. Recent landslide hazard analyses were carried out under given probability of exceedance for a given ground motion, representing a conditional probability of earthquake induced landslides. In this study, we present a method for regional potential seismic landslide hazard zonation. In order to achieve this goal, we first summarize the main factors influencing the seismic landslide, particularly the inducing factor-strong ground motion. Based on the probabilistic seismic hazard analysis method and Newmark’s displacement model, we develop a new potential seismic landslide hazard zonation method Using the strong motion records from the Chi-Chi earthquake, Wenchuan earthquake, Tohoku earthquake and Lushan earthquake, we analyze the spatial distribution of Arias Intensity which is a effective indicator for the potential destructiveness of an earthquake in the form of seismic slope failure, and evaluate the applicability of some widely used Arias Intensity attenuation relationships by comparing the observed values with the estimates from empirical relationships. Finally, we apply potential seismic landslide hazard zonation method to the Tianshui earthquake-prone area. Based on the studies above mentioned, the following results and new understandings are obtained:(1) A preliminary method for potential seismic landslide hazard zonation is developed, in terms of probability based on the probabilistic seismic hazard analysis and Newmark’s displacement model, incorporating the effects of focal mechanism, site condition and topography. Different from the recent landslide hazard analyses which were carried out based on ground motions with given probability of exceedance, our method take the contributions of all the potential earthquakes for inducing landslide;(2) Using the strong ground motion records, we evaluate the applicability of some widely used Arias Intensity attenuation relationships, and analyze the spatial distribution of Arias Intensity, including the influence of fault strike, the hanging wall effect, rupture directivity effect and slope topography effect on Arias Intensity. These provides an invaluable reference for potential seismic landslide hazard zonation using Arias Intensity parameter and the developement of Arias Intensity attenuation relationship for China, and it is of great value for further understanding the formation mechanism of earthquake landslide and the formulation of countermeasures for disaster reduction;(3) Finally, a case study is carried out in theTianshui earthquake-prone area using our new probabilistic seismic landslide hazard zonation method, combining the potential seismic source zone used for the new generation seismic zonation map of China, empirical engineering geology lithology formations, and topographic slop data. A regional seismic landslide probability hazard map in future 50 years is obtainted. The results show that the high hazard zones mainly concentrated at the loess or mudstone areas with slope greater than 30 degree, especially on the banks of Wei River, Xi River and Niutou Revier, posing a threat to Longhai Railway line and the surrounding of Tianshui city, and these provide a reference for land planning and seismic landslide risk assessment and management.