The Anomaly Field of Subsurface Fluids and Its Formation and Evolution Mechanism Before Three Strong Earthquakes in the Northern North China Area

The data of pre-seismic subsurface fluid anomalies of such earthquakes as Datong-YanggaoM_s6.1 event on Oct.19,1989,western Baotou M_s6.4 event on May 3,1996 and Zhangbei-Shangyi M_s6.2 event on Jan.10,1998 are systematically collected and arranged.Then thefeatures of patterns,spatial distribution,time variation and time-spatial evolution of theseanomalies are compared and comprehensively analyzed.Then the formation and evolutionmechanism of medium-and short-term anomaly field of subsurface fluids in the northernNorth China area is proposed.The results show that the medium-term anomaly field is causedby regional tectonic activities,which further strengthen the local tectonic activities andpromote the formation and evolution of the seismic source body.The enhancement of loealtectonic activities causes the formation of anomaly field of short-term subsurface fluids,andthe evolution of source body engenders the source-precursor anomalies of subsurface fluids inthe epicenters at imminent stage.

The data of pre-seismic subsurface fluid anomalies of such earthquakes as Datong-Yanggao Ms6.1 event on Oct. 19, 1989, western Baotou Ms6.4 event on May 3, 1996 and Zhangbei-Shangyi Ms6.2 event on Jan. 10, 1998 are systematically collected and arranged. Then the features of patterns, spatial distribution, time variation and time-spatial evolution of these anomalies are compared and comprehensively analyzed. Then the formation and evolution mechanism of medium- and short-term anomaly field of subsurface fluids in the northern North China area is proposed.The results show that the medium-term anomaly field is caused by regional tectonic activities, which further strengthen the local tectonic activities and promote the formation and evolution of the seismic source body. The enhancement of local tectonic activities causes the formation of anomaly field of short-term subsurface fluids, and the evolution of source body engenders the source-precursor anomalies of subsurface fluids in the epicenters at imminent stage.