关键词: 应力降, 错动速度, 主应力方向, 突发失稳判据

Abstract: The analysis of hypocenter parameters by the tectonophysical method from data of earthquake cases shows that the stress drop,Δτ_sei is proportional to the slide velocity along a fault,V_sei,and the ratio (Ω=V_sei/Δτ_sei) is affected by the acting direction of principal stress,expressed by the slide angle θ. The frequency distribution of ratio Ω for a large amount of earthquake cases approximates to the Gaussian distribution with a mean value of Ω equal to about 0.092,which corresponds to the dominant sliding angle of about 60?. The proportional relationship between V_sei and Δτ_sei proves further the reasonableness of selecting stress drop to be an index of the sudden-instability criterion for earthquakes. In addition,the dependence of Ω on θ provides a new possible approach to estimating the direction of the principal stress.

Key words: Stress drop, Slide velocity, Direction of principal stress, Sudden-instability criterion