Study of the Relation Between the Features of Fault Deformation Tendency Anomaly and Earthquake Activity in the West of China

Using the tendentious accumulation rate of crustal deformation, Dc, the spatial distribution features of deformation across fault in the West of China was studied; the regional patterns of deformation accumulation induced by fault activity was established and its seismogenic meaning was discussed. The types of fault deformation evolution in the time domain and the features of change of large extent anomaly in fault deformation which occurred in 1995-1996 was analyzed comprehensively. It was indicated definitely that 1995-1996 is the turning point of fault network activity in the West of China since the 1990s; it is closely related to the change of main seismic active regions in the West of China, i.e., the alternation of strong/ weak stages and the change of action range of tectonic stress field in the Qinghai-Tibet block and its environs; and hence it is of medium- and short-term precursor meaning for the change of the overall pattern of earthquake activity in the West of China in the year 1996. On such a basis, a preliminary investigation of the mechanical mechanism and block movement background was made. We hold that the formation of NE-trending band of Ms6.0 earthquakes in 1988-1996 and NW-trending band of Ms5.0 earthquakes in 1997-1999 can prove in mechanics that the West of China is now in a state that the N-S stress weakens relatively but E-W stress strengthens relatively and predominates.