Identification of seismogenic faults between focal nodal planes based on tectonic stress fields with applications to the Yingjiang area

In order to identify the actual seismogenic fault plane in the nodal plane of the focal mechanism, based on the inversion result of the stress field at hypocenter, we made further calculation on the fault instability of the two nodal planes of focal mechanism, and regarded the most unstable one as the actual seismogenic fault plane. In this study, we applied the above methods to Yingjiang area of Yunnan Province, where abundant seismic data are obtained and the seismogenic structures of moderate earthquakes are well studied, and obtained the following conclusions: (1) The seismogenic faults of the earthquakes on March 21, 2008 and March 10, 2011 are NEE nodal planes of the focal mechanism, corresponding to Dayingjiang fault near the epicenter ; The seismogenic fault of the August 21, 2008 earthquake is the NS-oriented nodal plane of the focal mechanism which corresponds to the nearly NS-oriented Sudian fault near the epicenter ; The fault plane recognition result of the earthquake on May 23, 2014 is NEE nodal plane, and we infer that its seismogenic fault is Xima-Panlongshan fault ; The seismogenic fault of the May 30, 2014 earthquake is the NS nodal plane of the focal mechanism, and its seismogenic fault may be a fault parallel to the Sudian fault. (2) The identification results of the overall fault plane in Yingjiang area show that the seismogenic faults are nearly NS-oriented and NEE-oriented, which means that the seismogenic faults are conjugate faults, and the maximum compressive principal stress in the study area is NNE-oriented ; The relationship between the overall fault orientation and the direction of the maximum compressive principal stress axis is in accords with Anderson fault theory. (3) This research shows that the method of identifying the seismogenic fault plane in the nodal plane of the focal mechanism based on the tectonic stress field has clear physical significance, and the practical application results are reasonable and reliable.