Geometry of Seismogenic Faults Determination of the 2021 Maduo Earthquake Sequence by Fuzzy Clustering Algorithm

To gain a deeper understanding of the geological structure in the Maduo region of Qinghai, it is crucial to accurately determine the shapes and parameters of each branch fault planes in the area. Based on the principle that clusters of small earthquakes occur near the fault plane, by using the fuzzy clustering algorithm to cluster the seismic event, the geometry parameters of the fault planes of the 2021 Ms7.4 Qinghai Maduo earthquake sequence are determined. By projecting the stress field in study area onto the obtained fault planes, the relative shear stress and normal stress of each fault plane are obtained. The results show that the overall fault plane of these 2021 Maduo earthquake is mainly distributed on the Kunlun Pass-Jiangcuo fault, with rupture length of 163.71 km, strike of 285.81°, and dip angle of 85.62°. There are obvious bifurcations on the east and west sides of the earthquake distribution area. For the complex fault structure, we made various attempts through the fuzzy clustering algorithm, and obtained the fault plane solution by fuzzy clustering with 6 fault planes. By projecting the tectonic stress field onto the 6 obtained fault planes, we found that the relative shear stress on these fault planes is generally greater than the relative normal stress. Therefore, it is speculated that the earthquake was mainly caused by the tectonic stress field, and the small fault in the north branch at the western end of the bifurcation is the branch rupture caused by the main rupture. Due to the left-lateral strike-slip nature of this rupture, tail extension appeared in the northeastern part of the eastern segment of the fault, resulting in the formation of the 2 small faults on the bifurcation of the eastern segment. The fault parameters obtained by the fuzzy clustering method in this study are also highly consistent with the data of other authors and institutions. This method is an accurate and maneuverable method to obtain fault plane information based on a large amount of seismic sequence data. This method will have important significance for seismic structure, fault plane determination and analysis in the future.