Abstract: Differently from the existing studies, about 210 days of the original seismic recordings since the Ludian M_S6.5 earthquake are collected from almost all of the nearby stations, and a velocity model and a non-linear location technique are specially selected, in order to relocate the sources of the earthquake sequences. What is more, the same model as used in determining the absolute locations is adopted as the DD technique is used to determine their relative locations. Then the strikes and dips of the seismogenic faults are estimated by linearly fitting the source locations, and finally a new explanation is proposed for the sequence formation. It is shown that the sequence may be divided into 4 sub-areas spatially, each of which corresponds to a nearly vertical fault with but different dimensions and striking azimuths, and that two of them are relatively larger and linked with each other, being the main faults of the sequence, and two others are relatively smaller and separated away from the main faults. These 4 faults, together with the local existing faults, form a radiating-shaped structure reflecting the complicated tectonics, which is very likely to be related with the density variation in lower crust.

Key words: the Ludian M_S6.5 earthquake, relocation of the earthquake sources, determination of the seismogenic faults, cause of the seismogenic faults

摘要： 文中收集了震后约210d震区几乎所有台站的地震记录，特别挑选了速度模型和非线性定位技术，重新确定了鲁甸M_S6.5地震序列的震源位置，而且利用与绝对定位时相同的速度模型借助双差定位技术确定了它们的相对位置。基于定位结果，通过震源位置的直线拟合估计了发震断层的走向和倾角，并为发震断层的成因提供了新的解释。结果表明，此地震序列可分为4个区域，对应于4个尺度和走向不同但近乎直立的断层，其中2个较大且相互铰接，是地震序列的主要断层，另外2个较小且距主震相对较远；这4个断层与当地固有断层一起形成以震中为中心的辐射状结构，呈现出复杂的发震构造，而这种构造的形成很可能与下地壳物质密度的变化有关。

关键词: 鲁甸M_S6.5地震, 震源重新定位, 发震断层确定, 发震构造成因