关键词: 模糊聚类, 断裂带形状, 离群点数据, 主成分分析, 2021年漾濞地震序列

Abstract:

The rupture process of earthquake generally involves multiple fault activities. The seismogenic fault is generally not a single fault plane, but a combination of multiple fault planes. Based on the principle that clustered small earthquakes often occur near the fault plane, and assuming that the hypocenters obey three-dimensional normal distribution around the center of the sub-fault planes, the three-dimensional spatial structure of the Yangbi earthquake fault in Yunnan Province is estimated based on the fuzzy clustering algorithm. The results in this paper are estimated from the perspective of data analysis. The results will be more accurate if the comprehensive analysis can be carried out in combination with geological, geophysical exploration and other means. The fuzzy clustering analysis is mainly carried out for regions with dense seismic source data. Because the program compiled by this method runs fast on an ordinary computer and can be calculated many times in a short time, the best result can be obtained. In this study, the shape of fault zone can be quickly calculated and analyzed, the shape and spatial distribution of branch fault zone is roughly consistent with the seismic distribution, which verifies that this method has certain predictive effect and application value.
Firstly, GK(Gustafson, Kessel)fuzzy clustering method is used to obtain the partition matrix for all sub classes of hypocenter, then the outliers are removed by using the partition matrix and appropriate threshold, and the subclasses containing fault planes are extracted. Finally, the parameters of each fault plane(including position, strike and dip)with 95%confidence level are determined. It is inferred from the results that the hypocenters are distributed along the fault zone almost parallel to the Weixi-Qiaohou Fault and gradually divided into three fault branches to southeast direction. The east branch dips to southwest, which is the main fault, corresponding to two sub fault planes, with strike of 134.22°, 132.65°and dip angle of 87.14°, 81.96°, respectively; the west branch nearly parallels to the east branch with strike and dip of 129.45°and 74.77°, respectively. Except for the three main faults, a blind fault near the Weixi Qiaohou fault zone is identified in this study, with a strike of 235.66°and dip of 66.30°. In this study, we determined the fault structure of the Yunnan Yangbi earthquake sequence by fuzzy clustering algorithm, which is independent of other methods by using seismic wave data, geodetic data and geological data. It is of significance for tectonic and geodynamic studies.
This data analysis algorithm can be applied to the shape analysis and prediction of fault zone by a large number of such source data. In consideration of earthquake prediction and earthquake disaster assessment, the knowledge of fault network structure in the vicinity of large earthquakes will also help to test different assumptions about stress transfer effects.

Key words: fuzzy clustering, geometry of seismogenic faults, outlier data, principal component analysis, 2021 Yangbi earthquake sequence