红河断裂带两侧地震震源机制及构造意义

红河断裂带是一条大型的走滑断裂带。根据印支半岛前新生代的古地块与华南地块的接触关系 ,将红河断裂带海陆部分分为两段。断裂带自第三纪以来 ,经历了左旋运动、右旋运动 ,南北两段的活动性有一定的差异。根据断裂带两侧地震和震源机制解分析 ,震源深度 0～ 33km的地震在整个区域密集分布 ,较深的地震分布在断裂的北东侧。断裂带西北部断裂活动方式为逆冲型 ,北部为正断型 ,南部为走滑型 ,其它地方为奇异型 ,也即是逆冲型、正断型、走滑型 3种方式的过渡类型 ,反映了红河断裂带及其周围地区受到来自北北西向的推挤力和北东东向的正压力的联合作用 ,使受力区的断裂发生挤压逆冲、水平走滑和拉张正断运动。

EARTHQUAKE FOCAL MECHANISM AND ITS TECTONIC SIGNIFICANCE ALONG THE TWO SIDES OF THE RED RIVER FAULT ZONE

The Red River Fault Zone is a gigantic strike-slip fault zone extending from Tibet to South China Sea for up to 1000 km. It has been divided into the north, central and south segments based on the difference of the geometry, kinetics, and seismicity in the land. Based on the contact relationship between the old pre-Cenozoic massif in Indosinian Peninsula and the South China massif, the Red River Fault Zone was divided into two parts extending from land to ocean, i.e., north and south segments. Since the Tertiary period, the Red River Fault Zone suffered both of the sinistral movement and dextral movement, but the activities of the north and the south segment were different. Based on the analysis of earthquakes and focal mechanism solutions, earthquakes with focus depth varying between 0～33km are distributed in the whole region while deeper earthquakes are distributed in the northeastern sides of the fault belt. Types of faulting activities are thrust in the northwest, normal in the north, strike-slip in the south and odd (transition type) in other regions. These show that the Red River Fault Zone and its adjacent region suffered the extrusion force in NNW direction and normal stress in NEE direction, which resulted in the extrusion-thrust, horizontal strike-slip and extensional normal movement of the fault in the region.