Preliminary research to determine stress districts from focal mechanism solutions in Southwest China and its adjacent area

The method of sliding direction fitting is used to determine stress districts, taking the shear stress directions and ratios of shear stress to stress on fault planes given by focal mechanism solutions as the criteria to select focal mechanism solutions of one region and sorting out the earthquakes controlled by different tectonic stress fields, and then determining the stress districts from epicenter distribution of earthquakes. We call this method as step by step convergence method. By inversion analyzing of 297 focal mechanism solutions, we consider that Southwest China and its adjacent area can be divided into 5 stress districts, and we worked out directions of the three principal stresses and values of shape factor φ in 5 stress districts. Contribution No. 1999A0005, Institute of Crustal Dynamics, China Seismological Bureau. This subject is supported by the Chinese Joint Seismological Science Foundation (97-07-424) and SSTCC Climb Project 95-S-05.