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通常认为断层永久位移产生的小“静态”应力变化可以改变附近断层上发生地震的可能性或者说可触发地震(Harris,1998)。许多近场的触发地震,特别是触发余震的研究(Dieterich,1994;Toda,et al,1998;King,et al,1994),将这种静态变化视为触发因素,并认为它与断层上负载的变化是等价的(Toda,et al,1998;King,et al,1994;Jaume and sykes,1992;Harris and Simpson,1992)。这里我们报道矩震级Mw=7.3的兰德斯地震的余震图象与应力变化的比较,不仅与静态应力做对比,而且与地震波传递的瞬态、振荡应力变化(即,“动态”应力)做对比。动态应力不会永久地改变加载情况,仅能通过改变断层区的力学状态或性质来触发地震。这些被动态弱化的断层在地震波通过后可能破裂,甚至能导致如果没有动态应力就不会发生的地震。我们发现余震和动态应力图象都具有类似的不对称性,动态应力来自于破裂的传播,而静态应力变化没有这种不对称性。先前的研究表明,动态应力在远距离处可促使破裂(Anderson,et al,1994;Gomberg and Bodin,1994;Gomberg,1996;Gomberg and Davis,1996;Hill,et al,1993,1995),然而本文表明在近处也是如此。
It is generally accepted that small “static” stress changes caused by permanent displacement of a fault can change the probability of occurrence of an earthquake in a nearby fault or trigger an earthquake (Harris, 1998). Many near-field triggered earthquakes, especially those that trigger aftershocks (Dieterich, 1994; Toda, et al., 1998; King, et al., 1994) consider this static change as a trigger and consider it to be associated with fault loading (Toda, et al, 1998; King, et al, 1994; Jaume and Sykes, 1992; Harris and Simpson, 1992). Here we report that the comparison of aftershock images and stress changes for a Landers earthquake with Mw = 7.3 not only compares with static stress but also with transient and oscillatory stress changes (ie, “dynamic” stress) of seismic waves Compared. Dynamic stress does not permanently change the loading situation, and can only be triggered by changing the mechanical state or nature of the fault zone. These dynamically weakened faults can rupture after the passage of seismic waves and can even lead to earthquakes that would not have taken place without dynamic stresses. We find that both aftershocks and dynamic stress images have similar asymmetry, dynamic stress comes from the propagation of rupture, and there is no such asymmetry in static stress changes. Previous studies have shown that dynamic stress promotes rupture at long distances (Anderson, et al 1994; Gomberg and Bodin 1994; Gomberg 1996; Gomberg and Davis 1996; Hill et al 1993, 1995), however, That is also true in the near.