基于构造应力场识别震源机制解节面中发震断层面——以盈江地区为例

为了识别震源机制解节面中的实际发震断层面,本研究在反演震源处应力场的基础上,进一步计算震源机制解两个节面的不稳定系数,将其中最不稳定的节面视为实际发震断层面.本研究将上述方法应用于地震资料丰富且中强震发震构造研究较为深入的云南盈江地区,获得以下结论: (1) 2008年3月21日和2011年3月10日地震发震断层为震源机制解中NEE向节面,对应震中附近的大盈江断裂; 2008年8月21日地震的发震断层为震源机制解中NS向节面,对应震中附近近NS向苏典断裂; 2014年5月23日地震断层面识别结果为NEE向节面,其发震断层可能为昔马—盘龙山断裂; 2014年5月30日地震的发震断层为震源机制解中NS向节面,其发震断层可能是与苏典断裂平行的断裂.(2)盈江地区总体断层面识别结果显示盈江地区发震断层走向优势分布为近NS向和NEE向,呈现出共轭断层,研究区最大主压应力方向为NNE向; 断层走向和最大主压应力轴走向关系符合安德森断层理论.(3)本研究表明基于应力场识别震源机制解节面中发震断层面方法物理意义明确,实际应用结果合理可靠.

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.