关键词: 地下流体, 前兆, 区域应力场, 震源应力场, 新疆

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