基于可靠度理论的水库诱发地震分析

RELIABILITY BASED ANALYSIS ON RESERVOIR INDUCED EARTHQUAKES

分析了水库诱发地震的影响因素,详细阐述了库水在诱发地震中起到的作用;将诱发水库地震的因素——断层面的产状、摩擦系数、凝聚力、应力状态、孔隙水压力视为随机变量,基于断层面的库仑应力,建立断层发震的功能函数,并应用可靠度理论,分析各主要因素对发震概率的影响。经一特定实例分析表明:1)随着断层面孔隙水压力的增加,断层发震概率大幅度增加;在孔隙水压力均值相等的条件下,随着发震部位孔隙水变异性的增加,发震概率明显增加;2)走向与水平向大主应力方向一致的断层和倾角>60°的陡倾角断层更容易诱发地震;3)水平向小主应力对诱发地震的影响较大主应力大得多,水平向小主应力越大,断层越稳定,诱发地震的概率越小;4)随着断层面的摩擦系数和凝聚力的增加,断层的发震概率逐渐减小,但断层面摩擦系数对诱发地震的影响较断层面的凝聚力大得多。

Reservoir induced earthquakes（ RIE） are caused by impoundment of reservoir, with the characteristics of small magnitude and shallow focal depth,but they can also lead to not only economic loss,but also many serious secondary disasters,such as dam destruction,landslide,producing greater damages far more than the damages directly produced by earthquakes. So study on RIE is quite significant in the field of dam construction,thus more attentions should be paid to RIE. There are many factors to induce reservoir earthquakes,such as geological condition,rock mass mechanical index,state of crustal stress,pore pressure distribution,all of which are extremely difficult to measure due to the presence of many randomness; even if applying most advanced methods to measure them,the values fluctuate in great range,without a certain value in time and space. The great variety of these parameters gives rise to troubles to analyze RIE by deterministic approaches. How to handle the randomness of these factors has become vital problem in the field of RIE research. In this study,based on probability theory,and taking the main influence factors as stochastic variables,a new method to analyze probability of RIE was proposed by applying reliability theory. Firstly,the factors inducing reservoir earthquakes were analyzed,of which pore pressure in fault caused by water impounding of reservoir plays a vital role in triggering earthquakes. Then,taking these factors,including attitude,friction coefficient,cohesion of fault plane,stress state of fault plane and pore pressure in fault,as stochastic variables,performance function of triggering earthquakes was established by applying Coulomb stress on the fault plane,and reliability theory was used to analyze probability of earthquake induced by main factors. A special case analysis showed that：（ 1） The probability of induced earthquakes dramatically increases as pore pressure in fault increases; under the condition of equal pore pressure at triggering earthquakes area,probability of induced earthquakes obviously rises with enlarging of variation of pore pressure;（ 2） those faults with strike approximately parallel to horizontal maximum principal stress direction or with steep dip angle about more than 60° are prone to inducing earthquake;（ 3） as horizontal minimum principal stress increases,which has greater effect on induced earthquakes than horizontal maximum principal stress,probability of induced earthquakes becomes lower and fault keeps in more stable condition;（ 4） probability of induced earthquakes gradually decreases with the increase of friction coefficient and cohesion of fault plane; However,the effect of friction coefficient on induced earthquakes is much greater than the cohesion of fault plane.