2013 年洱源MS5. 5 地震震区地质构造复杂，发育有NW 向和NE 向2 组活动断裂。据野外调查和探槽揭示，震中附近的维西-乔后断裂为晚第四纪活动断裂，其新近活动时代主要在晚更新世晚期，全新世仍有较明显的活动迹象，运动性质以右旋走滑为主兼有正断。此次地震等烈度线呈NNW 向的椭圆形展布，极震区达Ⅶ度，长15km，宽10km，面积约279km2。震源机制解显示:该震源断层为正断兼走滑破裂型，与维西-乔后断裂的运动学特征基本吻合;节面Ⅱ为NW 向，与维西-乔后断裂走向基本一致。结合地震烈度分布、滑坡崩塌体分布和微震分布特征等分析推断，此次地震的发震构造应为维西-乔后断裂。震区地处滇西北横断山脉腹地，巨大的地形高差，强烈的表层岩石风化，是造成此次地震破坏较重的自然地理条件，而居民房屋多为抗震性能差的土木结构和砖木结构等简易建筑，是造成地震灾害加重的构筑物背景。

The geological structure of the Eryuan MS 5． 5 earthquake area is complex，with the two fault groups striking NW and NE． The filed investigation and exploratory trench showed that the Weixi-Qiaohou fault nearby the epicenter is one of the late Quaternary，with its new activities mainly in late Pleistocene． The signs of its activities can be found in Holocene，The movement is mainly of right lateral slipping with some normal faulting． The seismic intensity of this earthquake distribute as an ellipsoid with a NNW direction，and the intensity of meizoseismal area is up to Ⅶ，with a total area of around 279km2，15km in length and 10km in width． The focal mechanism result reveals that the earthquake source is in normal faulting and strike slipping，consistent with the kinematics characteristics of the Weixi-Qiaohou fault，and that the nodal section Ⅱ has a NW direction，basically consistent with the strike of the Weixi-Qiaohou fault． Combining with the distribution features of seismic intensity，the landslide and collapse，and micro earthquake，we believed that the earthquake was generated by the Weixi-Qiaohou fault． The earthquake area is located in the interior of the Hengduan Mountains，northwestern Yunnan． The great terrain relief and the intense weathering of the surface rock are the physical geography situation of the serious damage． The inhabitant is living in simple mud-wood structure or brick-wood structure building with poor seismic performance，and it is the social reason of the serious damage． In order to decrease earthquake losses，we need to increase the infrastructure in the remote rural areas，to improve the living environment in the countryside，and to enhance the seismic performance of the residential building．

国家自然科学基金项目(41472204)、地震行业专项(201108001)资助