中国大陆西部及周边地区地震活动特征的研究

CHARACTERISTICS OF SEISMIC ACTIVITY IN WEST CHINA AND ITS SURROUNDING REGIONS

探讨了中国周缘板块的联合作用对中国大陆地震的控制和影响 ,进一步研究了中国大陆西部及周边地区的地震活动特征。结果发现 ,该区域的地震活动除了有高潮和低潮的轮回特征外 ,还有相互消长的关系 ,并且地震相互消长有一个特定的比例。这一特点 ,对于中国大陆强震活动主体区的预测 ,尤其是对地震高潮期的结束时间提供了一个判据。

China's continent lies at the southeastern corner of the Eurasian Plate. It is squeezed by N-NNE-trending compressional force of the Indian Plate in the southwest, influenced by the NW- NNW -trending subduction zone of the Pacific and Philippine Plates in the east, and confined by the Siberian- Russian block of Eurasian Plate in the northwest. According to the data obtained from 22 GPS stations in 1994 and in 1996, it is suggested that the horizontal relative motion of China's continent is mainly compressional in north-south direction, and weakly tensile in east-west direction. Taking the North-south seismic belt as a boundary, the crustal movement is stronger in the west and weaker in the east, while the motion along block boundaries is dominated by sinistral compressional shearing. This situation may indicate that the crustal motion of China's continent is dominated by the northeastward squeezing of Indian plate. In addition, it is suggested that the most prominent and most important tectonic motion in China's continent should be the India-Eurasia collision, which causes crustal deformation in a vast regions including the rise of the Qinghai-Xizang Plateau and the formation of a series of seismic belts. Considering the west China and its surrounding regions as a uniform seismic zone, we discuss in this paper the control and influence of the joint action of the surrounding plates on continental strong earthquakes of China. In addition, the characteristics of seismic activities in West China and its surrounding regions are discussed as well. We find that the temporal distribution of strong earthquakes in this seismic zone is characterized by rhythmicity. According to the spatial migration of strong earthquakes, this region can be geologically divided into two seismic zones: the collision zone and the influenced zone, bounded by the suture zone between Lasa and Qiangtang blocks. We find that the earthquake activities in these two zones are interactively increased and decreased. The discovery of this feature will be useful in the assessment of the intensity of seismic activity in the broad North China.