中国西南部强震带大震复发机制

RECURRENCE MECHANISM OF LARGE EARTHQUAKES IN STRONG SEISMIC BELTS IN SOUTHWEST CHINA

我国西南部鲜水河断裂带、红河断裂带、安宁河断裂带和龙门山断裂带四个测区内，用Ｘ射线法测得的宏观残余应力场和用震源机制解Ｐ轴显示的发震时现今应力场的水平最大主压应力方向基本吻合。这种叠加应力场的水平最大主压力分布方向与发震断裂带总体走向的交角约为４０～５５°左右，使断裂带易于发生剪切错动。宏观残余水平最大剪应力高值区的分布，也与区内大震震中的分布基本吻合。岩石裂面在３００℃和３００ＭＰａ围压下经１０天便重新烧结起来，而具有很高但低于原岩的抗剪强度。这种烧结面，在残余和现今应力叠加场的水平最大剪应力作用下再剪断而发震，应是我国西南部震源在１０公里深以下大震复发的重要机制。

The distributive directions of horizontal major principal compressive stress of the macro-residual stress field determined by X-ray method and the present stress field indicated by P axes during the occurrences of earthquakes are basically coincided in the 4 measuring areas of Xianshuihe, Honghe, Anninghe and longmenshan fault belts in southwest China. The angles between the distributive directions of horizontal major principal compressive stress of this superposition stress field and strikes of fault belts during occurrences of earthquakes are about 40°-55°, which is easy to cause shear dislocation in the fault belts. The distribution of high value area of macro-residual horizontal major shearing stress are also coincided with the distribution of epicenters of the large earthquakes in measuring areas. The fracturing surfaces of rock are sintered at 300℃ and 300 Mpa of confining pressure for 10 days, which have high strength of shearing resistance, but lower than that of original rock. Under the action of horizontal major shearing stress of residual and present superposition stress field, the sintered surfaces fail and earthquakes occur, which should be an important mechanism for recurrences of large earthquakes with depth greater than 10 km.