The stress change of the major activity faults in the Weihe Graben after the Wenchuan earthquake

The seismicity of small earthquakes in the Weihe Graben has changed after the Wenchuan earthquake. In detail, the seismicity around the Qishan-Mazhao fault in the western Weihe Graben decreased, while the seismicity in Gaoling and Jingyang Counties in the middle portion of the Weihe Graben and that in the area between Hancheng and Yuncheng Cities in eastern Weihe Graben increased. In this paper, the stress loading on the major activity faults in the Weihe Graben induced by the Wenchuan earthquake is discussed based on the Coulomb stress theory. The results show that the Wenchuan earthquake has exerted an unloading effect in the western Weihe Graben and a loading effect in the middle and eastern Weihe Graben. The spatially varied Coulomb stress is consistent with the seismicity distribution, indicating that the seismicity change is closely associated with the stress loading caused by the Wenchuan earthquake.