根据走滑大地震前后应力轴偏转和应力降求取偏应力量值的研究

运用走滑地震造成的地震前后应力方向偏转和地震应力降Δτ推导得到地震震源处偏应力量值τ的解析表达式为τ=［Δτcos2(φ′[KG-*2]P-E)］/sin2(φ′[KG-*2]P-φP)(其中，φ-P和φ′[KG-*2]P分别为地震前后的统计P轴走向，E为地震断层走向.).当震前P轴与震后P轴与断层走向夹角为45°时，该公式失效.对偏应力值与应力降比值随应力场主压应力轴与断层走向夹角及应力场主压应力轴偏转的变化进行分析表明，相同应力降造成的应力轴偏转越大，地下偏应力越小; 断层走向越接近主压应力轴方向，地震应力降场对偏应力场的贡献越小.将该方法运用于Landers地震震源区，求得了该地震Homestead Valley段的偏应力量值为10MPa.

Deviatoric stress level estimation according to principle axes rotation of stress field before and after large strike-slip type earthquake and stress drop

In order to get deviatoric stress level τ, the analytic formula is derived according to rotation of stress filed before and after strike slip type earthquake and the stress drop Δτ of the earthquake as follows:τ=[Δτcos2(φ′[KG-*2]P-E)]/sin2(φ′[KG-*2]P-φP)(φP and φ′[KG-*2]P are statistical strikes of %P% axis before and after earthquake, E is the strike of seismic fault.). The formula is invalid when the angle of preseismic P axis or postseismic P axis and strike of seismic fault is 45°. It is analyzed that the ratio of deviatoric stress level and stress drop of earthquake changes according to the strike angle of seismic fault and principal pressure axes of deviatoric stress field and rotation angle of principal pressure axes. We found that: (1) the larger of the stress filed rotation caused by the same stress drop, the smaller the deviatoric stress level; (2) the more approach of the fault strike to the principal pressure axes before the earthquake, the less contribution to the deviatoric stress level by the stress drop field. The importance of the formula is discussed. This method is applied in Homestead valley patch of Landers earthquake, the deviatoric stress level is estimated as 10MPa.