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.