关键词: 双震型地震, 破裂过程, 云南

Abstract: The Longling earthquake of M7.3 and M7.4 in 1976 and the Lancang Gengma earthquake of M7.2 and M7.6 in 1988 are two typical double main shocks occured in Longlin Lancang fault zone,Yunnan. Based on the seismicity analysis of the events,it is found that they have different characters. The Longling earthquake occurred in a block which composed mainly of the granite in which the structure is comparatively homogeneous. The focus machanism analyses of the Longling earthquake give the direction of compressive stress in NNW,the trace lines of the principle stress axis extends mainly in SN to NE. The direction of the seismogenic structures are in NNW to SN and NE to NEE. There are two intensity areas of 9 degree of which the long axes are nearly right crossed each other. The Lancang Gengma earthquake occured near an ancient plate boundary with complex seismotectonic background. The directions of principal compressive stress of the two main shocks given by focal mechanism analyses are different. The Gengma M7.2 earthquak occurred in an area in which the tectonic stress is mainly tensional in NW direction. While the principal compressive stress field of the Longling M7.6 earthquake is characterized by the fan shape in NS direction. The seismogenic structures of the Langcang Gengma earthquakes are of en echelon in NW direction. The axes of meizoseismic areas of two main shocks are parallel each other. Based on the comparison and analysis,the X-type model and triggering model of seismic rupturing for the double main shocks are proposed,and their features and formative condition are also disscussed.

Key words: Double earthquake type, Rupture process, Yunnan