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加州1992年兰德斯7.3级地震和1999年赫克托矿7.1级地震的接近和相似允许人们对触发地震的假设进行检验,而这在以前是不可能的。赫克托矿地震证实了对兰德斯地震所提出的推断:瞬时、振荡的“动态”形变以地震波的形式辐射,能触发地震活动速率的增加(Hill,et al,1993;Anderson,et al,1994;Gomberg andBodin,1994;Spudich,et al,1995;Gomberg,1996;Gomberg and Davis,1996)。在本文中,我们对地震活动速率的空间和时间变化(Mmthews and Reasenberg,1988)进行了量化。在兰德斯地震的北部地震活动速率增加,而对赫克托矿地震这种增加主要发生在震中以南。我们认为破裂方向性分别使兰德斯和赫克托矿断层的北方和南方动态形变提高,这可以由地震波速度场的不对称性得到证明。对于触发作用,动态和静态应力变化都很重要,距离较远处动态应力变化起主要作用。峰值波速证明了动态触发阈值的存在,并约束了动态触发阈值的范围。在大多数地区,这个阈值依赖当地的条件,从零点几到几MPa变化,超过静态阈值一个量级以上。在某些地点触发过程直到动态形变平息了之后才开始。这些观测现象的物理机制可能与导致液化和循环疲劳的机理相似。
The proximity and similarity of the California 7.3 Landers 7.3 Earthquake in 1992 and the 1999 Hector Mine 7.1 Earthquake have allowed people to test the assumptions that triggered the earthquake that were not possible before. The Hector Mine earthquake confirms the inferred hypothesis of the Landers earthquake that the “dynamic” deformation of the oscillations radiated in the form of seismic waves at a momentary moment, triggering an increase in the rate of seismic activity (Hill, et al., 1993; Anderson, et al. , 1994; Gomberg and Bodin, 1994; Spudich, et al, 1995; Gomberg, 1996; Gomberg and Davis, 1996). In this paper, we quantify the spatial and temporal variations in seismic activity rates (Mmthews and Reasenberg, 1988). The rate of seismic activity in the northern part of the Landers earthquake increased, whereas the increase in the Hector Mine earthquake occurred mainly south of the epicenter. We think that the directionality of rupture increases the dynamic deformation in the north and south of the Landes and Hector mine faults, respectively, which can be proved by the asymmetry of the seismic velocity field. For triggering, both dynamic and static stress changes are important, and dynamic stress changes play a major role at longer distances. The peak wave velocity proves the existence of a dynamic trigger threshold and constrains the range of dynamic trigger thresholds. In most regions, this threshold is dependent on local conditions, varying from a few to a few MPa, exceeding the static threshold by more than one order of magnitude. In some places the triggering process does not begin until the dynamic deformation subsides. The physical mechanism of these observations may be similar to the one that causes liquefaction and cyclic fatigue.