论文部分内容阅读
汶川地震(M_s8.0)形成了具逆冲兼右旋走滑性质的映秀-北川破裂带、纯逆冲性质的灌县-安县破裂带以及它们之间具左旋走滑-逆冲性质的小鱼洞破裂带,成为世界上迄今为止空间上分布最为复杂、长度最大的逆冲型地震地表破裂带。其地表破裂过程对理解发震机理具有重要的科学意义。文章根据地表破裂带的不同运动特性以及分段性,并结合不同地段同震断层擦痕行迹,探讨汶川地震地表破裂过程。通过详细分析,认为沿地表破裂带出现南北两个大的滑移量峰值,以及南北两段破裂带的几何分布和运动特性均不同,表明汶川地震是由南北两个次级破裂事件组成,这个结论与地震波数据反演结果一致,并根据八角庙和北川地区同震断层擦痕的运动学对比研究,推测汶川地震初期破裂以逆冲运动为主,沿映秀断裂和灌县-安县断裂,同时形成约100～80km长近纯逆冲性质的映秀-清平段地表破裂带和灌县-安县地表破裂带,并且在这两条破裂带向NE方向扩展过程中形成了小鱼洞地表破裂带。由于南部初期破裂事件触发了北川断裂的活动,造成后期破裂事件的发生。后期破裂事件以右旋走滑(或右旋斜冲)运动为主,沿映秀-北川断裂形成龙池-深溪沟-八角庙-清平-擂鼓-北川-南坝-石坎等一线破裂带,该破裂带在映秀断裂带上叠加了第一次破裂事件形成的部分破裂带,整体地表破裂带南段(映秀-清平段)叠加了两次不同性质的破裂过程,北段(擂鼓-北川-南坝-石坎段)只反映了第二次破裂事件的过程。所以,汶川地震地表破裂带中约270km长的映秀-北川破裂带具有逆冲兼右旋走滑性质,而约80km长的灌县-安县破裂带为纯逆冲性质。地震破裂过程是一动态复杂的物理过程,上述地表破裂模型可以解释两条不同性质破裂带的形成。但是否符合实际的地震破裂过程,还需要通过近台网地震波数据精细反演地震震源破裂过程的验证。
Wenchuan earthquake (M_s8.0) formed a Yingxiu-Beichuan rupture zone with thrust and dextral strike-slip properties, Guanxian-Anxian rupture zone with purely thrusting properties, and small-scale strike-slip-thrust nature between them The fish hole rupture zone has become the world’s most complex and lengthy thrust surface rupture zone so far. The surface rupture process has important scientific significance for understanding seismogenic mechanism. According to the different movement characteristics of the surface rupture zone and the segmented nature, the article discusses the surface rupture process of the Wenchuan earthquake in combination with the traces of the coseismic faults in different locations. Through detailed analysis, it is concluded that there are two large north-south slip peaks along the surface rupture zone, and the geometric distribution and movement characteristics of the two rupture zones are different. It shows that the Wenchuan earthquake is composed of two sub-ruptures of north and south, The results are in good agreement with the seismic data inversion results. According to the kinematic comparison between the coseismic faults in the octagonal temple and Beichuan region, it is inferred that the rupture of the Wenchuan earthquake was dominated by the thrust movement along the Yingxiu fault and Guanxian-Anxian fault, The Yingxiu-Qingping section of the surface rupture zone and the Guanxian-Anxian surface rupture zone of about 100 km-80 km in length are formed, and the surface rupture zone of the small fish-cave is formed during the expansion of these two rupture zones in the NE direction. As a result of the initial rupture of the southern part of the basin triggered the activities of the Beichuan fault, the rupture occurred later. The late-rupture event was dominated by dextral strike-slip (or right-lateral strike-slip) movement, forming the first-line rupture zone along the Yingxiu-Beichuan fault such as Longchi, Shenxigou, Bajiaomiao, Qingping, Leigu, Beichuan and Nanba The rupture zone superimposed the partial rupture zone formed by the first rupture on the Yingxiu fault zone, and the rupture process on the southern section (Yingxiu-Qingping section) of the whole surface rupture zone superimposed two different types of rupture processes. The northern section (Leigu- Beichuan - South Dam - Shek Kau) only reflects the second rupture of the incident. Therefore, the Yingxiu-Beichuan rupture zone about 270 km long in the surface rupture zone of the Wenchuan earthquake has the thrust and dextral strike-slip characteristics, while the Guanxian-Anxian rupture zone of about 80 km in length is purely thrust. The earthquake rupture process is a dynamic and complicated physical process. The above surface rupture model can explain the formation of two different types of rupture zones. However, whether it is in line with the actual earthquake rupture process or not, it is also necessary to verify the seismic focal rupture process by using the data of near-surface seismic waves.