Abstract: Based on digital seismograms of eastern Shandong and the surrounding areas recorded by the Shandong digital seismic network since 2008,using Brune modelcom bined with genetic algorithm, we inversely calculate the apparent stress values of 225 earthquakes above magnitude 2. 0 in eastern Shandong. Furt hermore, we discuss the relationship between apparent stress and magnitude, analyze spatial and temporal variation of apparent stresses, and through the tem poral and spatial variation of apparent stress to study characteristics of local stress state. The results show that, firstly, the apparent stress range of small earthquakes in eastern Shandong is between 0. 06~3.91 MPa and mean stress level is 0. 31 MPa, which can be used as background stress level in the area; secondly, the apparent stress elevates with the magnitude increases which is positively correlated with the magnitude, we can get quantitative statistical relationships in the area using the robust fit; thirdly, we calculate difference apparent stress by subtracting the computed apparent stress through magnitude from the calculated apparent stress value, which can response to local stress variations more truly. In addition, time variations of apparent stress show that stress in eastern Shandong is currently in accumulation and enhance phase, whichis possibly related to the recent earthquake swarm in eastern Shandong. Spatial distribution show .that high apparent stress concentration area is mainly distributed in the area of Anqiu segment in Yishu fault and Yantai areas.

Key words: Seismic source parameter, Apparent stress, Difference apparent stress, Eastern Shandong province