Abstract: The capital region of China emplaces dense seismic network in recent years, it is possible to solve small focal mechanisms. We gathered large earthquake focal mechanisms in last fifty years and moderate or small earthquake focal mechanisms between 2002 and 2004, and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different subregion show that the direction of the maximum principle compressive stress axe is toward N(43°～86°)E in the Beijing—Zhangjiakou—Datong region, toward N(38°～86°)E in Tangshan area, and toward N(79°～81°)E in Xingtai area. Inversion results of this paper are similar with previous results, and reflect the correctness of the approach. The results reveal the stress field distribution consistency and subregion difference in the capital region, and can provide reference for earthquake mechanism explanation and geodynamics research.

Key words: Focal mechanism, Grid search, Tectonic stress field, The capital region of China