Research on relationship between stress field variation and earthquakes in Shanxi area,China
山西地区应力场变化与地震的关系

Based on the focal mechanism solution database established by collecting 37 years initial motion of small earthquakes (1970~2006), the space-time evolution characteristics of small-earthquake integrated mechanisms in Shanxi fault zone are studied in this paper. The results indicate that small-earthquake integrated mechanisms in Shanxi fault zone are mainly dominated by strike slip normal faults, at the two ends dominated by extension tectonics and in the central region by shearing. The difference between the stress field of Huabei and the regional stress fields of Xinding and Taiyuan Basins is very large. The relationship between horizontal motions and earthquake activities in Shanxi fault zone is analyzed according to the 12 stages of re-measuring data of GPS monitoring network along the Shanxi fault zone (1996~2007). The results indicate that the Shanxi fault zone now is mainly controlled by compressional stress along NWW-SEE direction and tensile stress along NNE-SSW. One obvious stress disturbance occurred during the period of 1998~1999, which was stronger in the south than in the north. This was followed by Datong-Yanggao M5.6 earthquake on 1st Nov.1999.