Abstract: A vast amount of observations have indicated that subsurface fluids (water, gas and oil) in deep crust, as an elastic medium, respond sensitively to the distribution, variation and transformation of deep crustal stress, as well as to the development, occurrence, adjustment and evolution of earthquakes. The generation of earthquake bears a close relation to the active intensity of regional tectonic stress. Under the background of large scale regional stress, a lot of stress concentration spots may form, which may give rise to the occurrence of premonitory anomalies of the subsurface fluids. The monitoring of subsurface fluids for several ten years in Xinjiang has discovered that a lot of earthquake related premonitory phenomena induced by the activity of regional tectonic stress occur before strong earthquakes. The space time patterns of the evolution of large scale premonitory anomalies of subsurface fluid occurred in 1998 and 1999 in north Tianshan region are emphatically analyzed in this paper. It is discovered that they are quite different in genesis and characters from the premonitory anomalies produced by stress activity at seismic source. It is suggested that this kind of premonitory anomaly field of subsurface water level should not be correlated to a single seismic event, but to a set or a series of earthquakes, which are often related to the activity of regional stress caused by block squeezing and fault activity. We select the No. 21, 25 and 26 springs as the sensitive spots in the monitoring area, and the differences between the premonitory anomalies induced by the activity of regional stress field and by stress field in seismic source are comparatively analyzed. The main purpose of the study is to get better understanding of field premonition and source premonition reflected by subsurface fluid, to distinguish and master their different characters, and to serve the earthquake prediction better.

Key words: Subsurface Fluid, Premonition, Regional Stress Field, Stress field at seismic source, Xinjiang

摘要： 大量观测事实表明,赋存于地壳深部的流体(水、气、油)作为弹性介质,对深层地壳应力的分布、变化、转移过程及地震孕育、发生等有着较为灵敏的反映.地震的形成与区域构造应力活动强度密切相关,这种大范围的区域应力作用会形成多个应力集中点,在众多应力集中点上可产生地下流体前兆异常变化.在对新疆地下流体数十年的监测中,发现强震前出现大量与地震有关的由区域构造应力活动引起的前兆异常,异常范围广且种类繁多,它们在成因、特征上与震源应力活动的前兆异常明显不同;这种地下水位地震前兆异常场,不能完全孤立地与单个地震事件相对应,应充分考虑到它与一组或系列地震有关,而这些地震往往与块体挤压、断裂活动等区域性的应力活动有关.因此,正确区分并掌握其不同的特性,对地震预报具有一定的意义.

关键词: 地下流体, 前兆, 区域应力场, 震源应力场, 新疆