Abstract: The southern Wudu M8.0 great earthquake occurred in 1879,many places in Wudu and adjacent areas had suffered destruction in various degrees. So far,the research results on the causative structure of this earthquake are less and inconsistent. Because it occurred in lofty mountains and the traffic is inconvenient,it is hard to make detailed field study on the earthquake site. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake,and referring to the morphology of the major axis of the meizoseismal area obtained by the predecessors,we selected a strip-shaped zone from the relocated earthquake catalog which occurred near the earthquake rupture zone in the period from 1985 to 2009 to calculate fault plane parameters of the earthquake,such as strike and dip,with the simulated annealing and Gauss-Newtonian nonlinear inversion algorithms. On this condition,the rake angles of the fault plane are further inferred from regional tectonic stress parameters. We discussed the causal mechanism of the earthquake and finally identified the length and location of the seismogenic fault. In addition,clustered small earthquakes occurred frequently in the Xionghuangshan area west of the mezoseismal area,but we didn't find clear fault planes in field investigation,so,they should not have relation with the 1879 M8 southern Wudu earthquake.

Key words: small earthquake clustering, the southern Wudu earthquake, least-squares solution, fault plane solution

摘要： 1879年武都南8级大震发生在高山峻岭之间,由于受自然环境和交通条件所限,一直难以进行详细的实地考察。到目前为止,关于此次地震的发震构造的研究较少且观点不一。依据成丛小震发生在大震断层面附近的原则以及参考前人给出的极震区长轴形态,我们采用1985-2009年发生在该地震破裂区的精定位地震目录,选定了一个长条状研究区域,将模拟退火算法和高斯-牛顿算法结合,给出了1879年武都南8.0级地震震源断层是一条长约30km、埋深2～23km的NNE走向、高倾角并在NNW-SSE向压应力作用下发生右旋走向滑动的断层。该区域地壳深部(H>24km)至今没有地震发生,推测震源断层没有扩展到地壳深部。震源断层位置在文县高楼山(33.01°N,104.74°E)和梨坪(33.22°N,104.90°E)之间。另外,我们发现在极震区以西的雄黄山地区小震成丛发生,但野外调查并未发现明显的断面,这些小震应该与1879年武都南8级地震没有关系。

关键词: 小震丛集, 武都南地震, 最小二乘解, 断层面解