复杂震源构造与地震滑坡分布：2014年云南鲁甸Ms6.5级地震解析

The 2014 Ludian, Yunnan Ms6.5 earthquake occurred in a mountainous area with complex tectonics and topography, which caused serious damage as well as co-seismic landslides of an unusual large scale. Because the suspected seismogenic faults on the surface, distribution of aftershocks and focal mechanism solutions are not consistent, it remains difficult to determine what is the real causal fault or seismogenic structure for this event. Actually it may imply the complicity of the seismic source at depth. Meanwhile, the distribution of the co-seismic landslides also exhibits some diffusion that is different from general cases, likely associated with the source structure. This project will be based on statistical analyses of correlations between the co-seismic landslides, seismogenic fault, topography, and lithology, as well as the data of the Ludian event that are verified and supplemented by field work. Using the Newmark physical model, the relationship between the seismic source structure and landslide distribution will be further analyzed. The new concept of contribution ratio of each causal factor to landslide distribution is proposed, by which a new expression of multiple-factor causal relationship of co-seismic landslide distribution will be established. The study area will be gridded. Supposing three possible models of seismogenic faults, input the corresponding seismic parameters as well as other variables of topography, lithology, special geological conditions, etc. into each grid element. The observed distribution of co-seismic landslides is fitted by trial calculation using the above relationship and input variables, choosing the optimal model to provide constraints for determination of most possible seismogenic structure. It can offer new insights to improve understanding the cause and mechanism of major earthquakes within continents. This study also represents an effort to find new approach for inversion seismogenic structure using co-seismic landslide data, or even applicable to research of paleo-earthquakes that have relict co-seismic landslides at the scene.

2014年云南鲁甸Ms6.5级地震发生在构造、地形复杂的山区，造成严重灾害与异常规模的同震滑坡。地表疑似发震断层、余震分布、震源机制解等不一致，使判别真实发震构造困难，暗示可能的发震构造的复杂性。同震滑坡分布格局也显示出与一般震例不同的异常特征。依据过去对大量震例同震滑坡分布与发震断层、地形、岩性等主控因素之间相关性的统计分析，以及补充、验证后的与鲁甸地震有关的地震构造与滑坡数据，本项目拟用Newmark物理模型，分析震源构造与同震滑坡分布格局之间的相关性，并提出各因素贡献率概念，建立同震滑坡分布多因素因果关系新的表达式. 将研究区网格化，假设多种可能的发震断层模型，向每个网格单元输入相应的地震控制参数及地形、岩性、特殊地质条件等变量，计算拟合鲁甸地震的滑坡分布，为推测可能性最大的发震构造提供约束，加深对大陆内部地震成因和机制的认识，为利用同震滑坡空间分布特征反演震源构造探索新的途径。

2014年云南鲁甸Ms6.5级地震发生在构造、地形复杂的山区，造成严重灾害。该地震触发了至少1024处面积 ≥ 100m2的滑坡崩塌，灾害程度超过了不少震级 ≥ M7.0级地震，而其触发的大型滑坡崩塌在同级别地震中更是鲜见。如红石岩滑坡规模巨大，堵塞了牛栏江而形成堰塞湖。地表疑似发震断层、余震分布、震源机制解等不一致，使判别真实发震构造困难，暗示可能的发震构造的复杂性。. 通过解译卫星影像建立了鲁甸地震滑坡分布数据库；同时开展多次野外勘察工作，对滑坡按规模、破坏形式进行分类；对研究区主要断裂：包谷脑-小河断裂、昭通-鲁甸断裂，龙树断裂等进行野外调查，建立了断裂与滑坡的关系，获得地形、岩体结构等条件对滑坡形成影响的认识。采用统计分析的方法，对该次地震滑坡的分布特点进行了研究，认为在中强地震条件下，高而陡的局部地形条件是形成众多大型滑坡的一个重要条件。同时，通过Newmark物理模型，对研究区的坡体临界加速度进行了计算。鲁甸地震诱发滑坡格局的特殊性之一是震中附近并不是滑坡分布最多，最严重的地方；之二是具有相同震中距、并且坡体临界加速度相同的区域，滑坡分布有很大不同。通过震区的坡体临界加速度分布与实际滑坡分布的对比研究，认为鲁甸地震滑坡受到震源构造的影响，因而在分布上出现了与以往认知不同的样式。鲁甸地震滑坡的空间分布受到了半共轭构造的控制，呈倒“L”型分布，与余震的空间分布非常契合。无论是近东西向的包谷脑-小河断裂，还是北东向的昭通断裂，单一断裂的破裂方式难以产生余震的分布状况，也不能诱发鲁甸地震同震滑坡的分布格局。半共轭方式的震源构造可以合理的解释鲁甸地震诱发同震滑坡的分布特点。. 本项目的研究成果表明，通过鲁甸地震诱发滑坡分布格局，反演震源构造的可能样式，是在同震滑坡与震源构造关系研究上的进一步探索。同时，Newmark方法获得的坡体临界加速度，能够体现坡体在地震作用下的稳定程度，在震后快速评估滑坡灾害中具有良好的应用前景。

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