A MODELING STUDY ON THE CONTROLLING FACTORS OF SEISMIC SOURCE DISTRIBUTION AND THEIR STRENGTH INDEX PRACTICAL ANALYSES OF THE SEISMIC ENVIRONMENTAL FACTORS OF THE RED RIVER FAULT

Zhang Chao; Xie Furen; ZHANG Shimin

doi:10.3321/j.issn:0253-3782.2001.02.002

Abstract：A model, in which various seismic environmental factors are involved, has been developed in the paper on the bases of relevant data. The environmental factors include the crust structure, lithological conditions, fault plan attitude, the crust stress state, pore-fluid pressure and geothermal conditions, etc. The influence of each of the factors to the tectonic movement energy index has been analyzed. The model calculation results indicate that shear fracture energy of a fault generally increases with depth; at a certain depth it reached a peak value, then turns gradually attenuated. Of all the factors, the influences of pore-fluid pressure and geothermal conditions to the energy index are of prominence. High pore-fluid pressure and high temperature circumstance may result in decline of the peak value of the shear fracture energy curve, making the depths of the peak value and of the bell-waist value deepened. Such effects restrict strong seismic events, but suitable for micro-seismic activity and/or fault creep. The lower limit of focal depth under such an environment is relatively deep. Contrarily, low pore-fluid pressure and low geothermal temperature circumstance result in increase of the peak value of the shear fracture energy curve, and the curve becoming steep. The later circumstance is favorable to the formation of locked segment where possesses high strength and high-energy accumulation. If these two kind of segments are arranged interactively along a fault zone, such arrangement would boost the energy transition among the segments, forming mechanical circumstance of energy highly accumulated in one segment with adjacent segment(s) less-locked. Such contrast of the strength and energy would provide conditions for strong earthquakes with high stress drop. An analysis of the northwest segment of the Red River Fault has provided some evidence to the modeling results.