由地震分布丛集性给出断层参数的一种新方法

由于大范围内地质构造的复杂性和介质的非均匀性,发震断层面的几何形态一般十分复杂.如果大地震的破裂过程涉及多个断层的活动,则发震断层并非是单一断层平面,而是多个断层面的组合.利用地震空间位置分布丛集性,即震源点成丛位于断层面附近的假设,结合稳健扩充算法和主成分分析给出一种可以重构活断层网络三维空间结构的新方法.该方法每次从震源点集中处开始,利用假设检验扩充子断层面,并得到多个子断层面.接着按震源点属于最近断层面的准则把各子断层面内的震源点进行竞争,并根据一定假设合并和删除一些子断层面,最后用主成分分析确定每个子断层面参数.于是可根据地震事件目录给出一组矩形区域来描述断层面网络结构,其中每个矩形断层面由其位置、走向和倾角确定.通过计算机模拟发现,新方法可成功地重建模拟地震目录的断层面,最后用于南加州1992年6月28日发生的Landers地震部分余震目录中,得到各个子断层面参数与已知地质破裂或隐伏断层相当一致.

A new method for determining fault planes parameters according to earthquake clustering

Because of the complex characteristics of the tectonic systems and medium heterogeneity in a wide region, the geometric shape of faults is usually complicated. If a major earthquake takes place, multiple faults are involved. And thus the fault planes are not a single fault plane but combined by several faults. We propose a new method that is able to reconstruct the three-dimensional structure of the active part of a fault network using the spatial location of earthquakes. Every time, the cluster consisting of neighboring several seismic events is selected randomly from the seismic events, and is gradually expanded by hypothesis testing, thus several clusters can be extracted. Subsequently, according to the criteria that any event point should be assigned to nearest cluster, the seismic events in extracted clusters are reassigned to different clusters. Some clusters are deleted or merged if they are too small or too close. Based on the remaining seismic event clusters, the parameters of fault planes are determined by the principal component analysis. So, given a catalog of seismic events, according to above procedure, we can find a series of rectangular-shaped fault planes which is characterized by its location, strike angle and dip angle to describe the spatial rupture structure of a large earthquake. The simulation results show that the algorithm successfully reconstructs the fault segments of synthetic earthquake catalogs. Applied to the real catalog constituted of a subset of the aftershock sequence of the 28 June 1992 Landers earthquake in southern California, the reconstructed plane segments fully agree with faults already known on geological maps or with blind faults.