依据断层摩擦准则估算的地壳主应力量值关系式及其参数分析

ESTIMATING THE MAGNITUDE OF TECTONIC STRESS BASED ON THE FRICTION CRITERIA OF FAULT AND ANALYSING THE PARAMETERS' INFLUENCE

基于Zoback(1992b)提出的估算地壳构造应力量值的思路和2个假设,考虑了3个主应力分别为垂直主应力(对应3种构造应力类型)的情况,比较系统地建立了依据应力形因子和断层摩擦强度估算构造主应力量值的关系式。讨论了摩擦系数、孔隙压力系数和应力形因子对构造主应力量值的影响:在最大主应力为近水平的情况下(应力类型为走滑型或逆断型),最大主应力量值(或随深度线性增加的斜率)随摩擦系数取值的增大而增大,随孔隙压力系数取值的增大而减小。在最小主应力为近水平的情况下(应力类型为走滑型或正断型),最小主应力量值(或随深度线性增加的斜率)随摩擦系数取值的增大而减小,随孔隙压力系数的增大而增大。并且,3个参数对主应力量值估算的影响很大,如果摩擦系数取值较大,同时孔隙压力系数取值较小,最大主应力随深度增加的斜率与最小主应力随深度增加的斜率之间的差异就大,有可能导致不合理的结果出现。该方法只是对地壳岩石发生脆性破裂或摩擦滑动时的构造应力量值进行近似估算,估算结果并不是地壳稳定状态下的构造应力量值。

Based on Zoback＇s method for estimating the tectonic stress magnitude and the two assumptions,we consider the conditions that three principal stresses are vertical principal stresses respectively（ corresponding to three kinds of tectonic stress types）. We deduced the formulae for estimating the tectonic stress magnitude by using the stress form factor and frictional strength of the fault and discussed the correlative influence of friction coefficient,pore pressure parameter and stress form factor on the stress value. When the maximum principal stress is approximately horizontal（ when stress regime is strike-slip or reverse）,the maximum principal stress（ or the slope of stress increasing linearly with depth） is positively related with the friction coefficient and negatively related with the pore pressure coefficient. When the minimum principal stress is approximately horizontal（ when stress regime is strike-slip or normal）,the minimum principal stress（ or the slope with depth） is negatively related to the friction coefficient,and positive to the pore pressure. Besides,these three parameters have great influence on the estimation of the tectonic stress magnitude. If the friction coefficient is too big and the pore pressure is too small,there could be a wide difference between the slope of the maximum principal stress increasing with depth and the slope of the minimum principal stress increasing with depth,which could lead to an unreasonable result. Our method is just an approximate estimation for the tectonic stress magnitude when crustal rocks have undergone brittle rupture or frictional sliding. The estimated results are not the tectonic stress magnitude when crust is in steady state.