Analysis of focal-mechanism solution of moderately strong earthquakes in Xinjiang from 1991 to 2002

In this paper, the authors gave out systemically focal-mechanism solutions for 44 moderately earthquakes in Xinjiang from 1991to 2002. The authors find out that Xinjiang is controlled by the horizontal compressional stress of NNE direction during this period, but the horizontal compressional stress of NW direction also exists clearly. There is a little difference from the background stress, in which the horizontal compressional stress shows a NS direction. During the period, the variety of focal-ruptures of moderately strong earthquakes shows the complexity of tectonic movement in Xinjiang. The change of elevation angles for F axes of principal compressional stress during different periods is associated with alteration of strong and weak seismicity in Xinjiang region. It shows the process that the stress field in Xinjiang built up and resumed. Many types of analyses show that from 1995-1996 the stress filed in Xinjiang has been clearly changed.