Abstract:

Seismic landslide is a kind of natural disaster in which the slope is unstable and slips under the action of earthquake. Unlike landslides triggered by factors such as rainfall, strong earthquakes in mountainous areas tend to trigger a large number of landslides over a wide area, which can cause more casualties and economic property losses than the earthquake itself in many cases. Moreover, the occurrence of earthquake-induced landslides is characterized by abruptness and concealment, so it is difficult to spot monitoring and prevention. In order to reduce the loss of earthquake-induced landslide disaster, scientists have developed a variety of prediction and evaluation methods for earthquake landslide hazard based on different theories and models through long-term research. The M_S7.4 earthquake, which occurred at 2:04 a.m. on 22 May 2021 in Maduo, Qinghai(34.59°N, 98.34°E), provided an opportunity to test the validity of the different models. On the one hand, based on the simplified Newmark displacement model, the susceptibility of seismic landslide in Maduo earthquake area is calculated. Furthermore, the seismic landslide risk is evaluated by combining with the seismic intensity distribution map after Maduo earthquake. On the other hand, based on the discrimination analysis method, the empirical model obtained from the Niigata earthquake in Japan is used to predict the earthquake landslide in Maduo earthquake area. The research results show that: Based on the rapid assessment of earthquake-induced landslide risk by simplified Newmark displacement model, the potential high-risk areas are mainly concentrated in the intensity area of Ⅷ, Ⅸ and Ⅹ which are greatly affected by the intensity of ground motion. On the whole, with the weakening of the impact of ground motion, the landslide risk decreases gradually, this is in good agreement with the actual situation. As an empirical model, discrimination analysis method is relatively dependent on a specific environment. When it is used out of its own environment, it is necessary to verify the universality of empirical formula, re-understand the relationship between various impact factors, and adjust the weight of each factor. The difference between the two methods in the prediction results is mainly in the seismic intensity Ⅵ region. In the areas with intensity VII and above, the risk zoning obtained by the two methods is generally consistent. Due to the differences in the research models adopted by the two methods, there are some differences in the distribution of seismic landslide hazard areas with different risk levels in the prediction results, especially in the Ⅵ intensity region. Intensity Ⅵ region is wide with more mountainous areas, and steep slopes are distributed in most of the areas. As a result, the discriminant analysis results in this area are more influenced by slope and curvature value, so there are more highly dangerous areas in the prediction results. However, the simplified Newmark method is greatly affected by the ground motion. Because this region is far away from the epicenter and the impact of ground motion is weak, so the main prediction results of this region show more low risk areas. However, in the intensity Ⅶ and above areas, the risk zoning of the two methods was generally consistent, and the prediction effect was good. In general, it can be seen from the prediction results that these two methods reflect their effectiveness to some extent. However, due to the different factors and fewer constraints, there are some differences in the results. In the seismic landslide risk assessment based on the discriminant analysis method, objective and complete landslide samples need to be fully analyzed, which is also a problem faced by the prediction method based on empirical model. As a physical model, Newmark model does not depend on the specific environment, although it has the problem in accuracy of input parameters, it is more objective and reasonable in the calculation results. In this paper, a simple evaluation and analysis of the Maduo earthquake was conducted based on the Newmark model method, which only considered the impact of slope itself and ground motion, but did not take into account hydrological factors, human activities, geomorphic factors and other conditions. Meanwhile, the Newmark evaluation method needs to obtain relatively clear rock-soil physico-mechanical properties and ground motion parameters, but it is difficult to obtain accurate data of each slope in practice, so there are still defects and deficiencies in regional risk assessment using this model. Compared with other traditional prediction methods based on statistical analysis, the physical meaning of this method is clearer, and it has irreplaceable advantages in combination with ground motion parameters. As a qualitative method, the discriminant analysis method uses the empirical formula derived from other earthquake cases to predict landslides. Engineering geological conditions are different in different earthquake regions, so the controlling factors of earthquake-induced landslide are not the same and the influence weight of each factor is different to some extent. Both qualitative and quantitative methods have their own advantages and disadvantages in the study of regional seismic landslide hazard prediction. It would take a long time to achieve accurate prediction of earthquake landslides.

Key words: Maduo earthquake, earthquake-triggered landslides, hazard analysis, Newmark model, discrimination analysis method

摘要：

地震诱发的滑坡(崩塌)是山岳地区强震过程中常见的一类地质灾害现象, 其造成的人员伤亡和经济财产损失常常超过灾害本身。为减轻和降低地震滑坡灾害带来的损失, 科学工作者们通过长期研究, 形成了多种基于不同理论和模型的地震滑坡危险性预测和评价方法。2021年5月22日2时4分发生在青海省果洛藏族自治州玛多县(34.59°N, 98.34°E)的 M_S7.4 地震为检验不同模型的有效性和适用性提供了机会。文中以玛多地震灾区的地形坡度数据、 地质岩性数据为基础, 一方面基于简化Newmark位移模型对玛多地震灾区的地震滑坡敏感性进行了计算, 并结合玛多地震震后的地震烈度分布图对地震滑坡危险性进行了评估; 另一方面以判别分析法为基础, 采用在日本新潟地震中获得的经验模型对玛多震区的地震滑坡进行了预测研究。研究结果表明, 基于简化Newmark位移模型的地震诱发滑坡危险性快速评估得到的潜在高危险区域主要集中在Ⅷ、 Ⅸ、 Ⅹ烈度区, 受地震动强度影响较大, 整体上随着地震动影响的减弱, 滑坡危险性逐渐降低, 与客观实际较为符合; 判别分析法作为经验模型, 比较依赖于特定环境, 在脱离其自身环境使用时要对经验公式进行通用性验证, 重新认识各个影响因子之间的关系, 调整各因素的权重。这2种方法在预测结果上的差异主要分布在Ⅵ度区, 在研究区Ⅶ度区及以上烈度区内, 2种方法得到的危险区划则大体一致。

关键词: 玛多地震, 地震滑坡, 危险性分析, Newmark模型, 判别分析法