Abstract: Based on propagation characteristics of the regional seismic body wave the authors try to determine and study the deviation coefficient of the initial amplitude of the seismic event, and to g et precursory information of moderately strong earthquakes. According to this idea the deviation coefficient of the initialamplitude of the seismic events is calculated from 1992 to 1999, latitude is from 38°N to 42°N and longitude is from 74. 5°E to 79°E in Xinjiang region of China ( from Wuqia to Keping along the Southern segment of Tianshan range). The possible precursors are discussed in tempo ral-spatial evolution process of this medium parameter around Atushi strong earthquake and Jiashi swarm. The research indicates that the strong earthquake happens in transitional a rea of the parameter variation; al so in an overage region with large change of the stress environment gradient. From the temporal view of point, the strong events usually occur at the period when parameter value from low er to higher or after it. The tectonic stress background of strong events is studied according to the physical sig-nificance of parameter in this paper.

Key words: Deviation coefficient of the initial amplitude, Precursory evolution in temporal-spatial scope, Tectonic stress background