Tectonic stress field in Shandong region inferred from small earthquake focal mechanism solutions

Based on 387 focal mechanism solutions of middle and small earthquakes occurred from 1970 to 2012,this paper studies the stress field in Shandong region by using damped regional-scale stress inversion. We adapted the conjugate gradient method to solve the damped optimization problem of stress tensors. According to the formulae derived by Lund and Townend we calculated the maximum horizontal principal stress orientations in this region. We also discussed the relationship between spatial variation of regional stress field and the Tancheng-Lujiang fault zone.