龙陵-澜沧断裂带双震型强震活动破裂模型讨论

龙陵地震和澜沧－耿马地震是龙陵－澜沧断裂带上两次典型的双震型强震活动，但它们在地质构造背景、应力场分布、发震构造和烈度分布等方面却具有截然不同的特点。龙陵地震发生在主要由花岗岩构成的地块内，地质构造比较均一；地震处在ＮＮＷ向挤压的统一应力场中；两主震的发震构造走向和两个Ⅸ度区长轴近于直交。澜沧－耿马地震发生在一古板块边界附近，震区构造复杂，耿马７．２级地震和澜沧７．６级地震发生于不同的应力环境中，发震构造和极震区长轴近于平行，呈斜列状分布。通过对龙陵地震和澜沧－耿马地震的对比分析，提出了双震型强震活动的共轭型和牵动型两种破裂模型，并对各自的特点及形成条件进行了初步分析

A STUDY ON THE RUPTURING MODEL OF THE DOUBLE MAIN SHOCK IN THE LONGLIN LANCANG FAULT ZONE, YUNNAN

The Longling earthquake of M 7.3 and M 7.4 in 1976 and the Lancang Gengma earthquake of M 7.2 and M 7.6 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 M 7.2 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 M 7.6 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.