震源分布和强度指标控制因素的模型研究──红河断裂地震环境因素的实例分析

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

参照并综合应用国内外相关资料、实验和研究成果 ,建立了一种涉及多种环境因素的模型 ,分析了不同因素对构造运动能量指标的影响 .其中包括地壳纵向结构、断层产状、岩性条件、地壳应力状态、孔隙压力和地温条件等 .模型计算结果表明 ,断裂的剪切破裂能随深度增加通常呈现先上升 ,在某一深度上达到峰值后逐渐衰减的形态 .在诸多因素中 ,孔隙压力和地温条件对能量指标的影响相对显著 .高孔隙压力和地温环境可导致剪切破裂能曲线的峰值降低、峰值和铃腰值所在的深度下移 .这种效应限制了强震事件 ,而适于中小地震活动或低能量释放的断层活动 ,其震源深度分布的下限较低 .反之 ,低孔隙压力和低地温环境使剪切破裂能曲线的峰值加大、形态变陡 ,其结果利于高强度、高能量积累的闭锁段的形成 .如果这两种段落在断裂带上相邻 ,则可能促进断裂带不同段落之间的能量转换 ,从而形成能量积累程度高而邻区锁定强度低的孕震环境 .红河断裂北西段温泉密度和热储温度分布与该地区的地震频度、强度和震源深度分布之间的关系与模型结果基本相符 。

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 effect of each of the factors on the tectonic movement energy index has been analyzed. The model calculation results indicate that shear fracture energy of a fault generally increases with depth; it reached a peak value at a certain depth, then turns gradually attenuated. Of all the factors, the effects of pore-fluid pressure and geothermal conditions on 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 Honghe fault has provided some evidence for the modeling results.