Kilb D, Gomberg J, Bodin P
Center for Earthquake Research and Information, The University of Memphis, Tennessee 38152, USA.
Nature. 2000 Nov 30;408(6812):570-4. doi: 10.1038/35046046.
It is thought that small 'static' stress changes due to permanent fault displacement can alter the likelihood of, or trigger, earthquakes on nearby faults. Many studies of triggering in the near-field, particularly of aftershocks, rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault. Here we report a comparison of the aftershock pattern of the moment magnitude Mw = 7.3 Landers earthquake, not only with static stress changes but also with transient, oscillatory stress changes transmitted as seismic waves (that is, 'dynamic' stresses). Dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone. These dynamically weakened faults may fail after the seismic waves have passed by, and might even cause earthquakes that would not otherwise have occurred. We find similar asymmetries in the aftershock and dynamic stress patterns, the latter being due to rupture propagation, whereas the static stress changes lack this asymmetry. Previous studies have shown that dynamic stresses can promote failure at remote distances, but here we show that they can also do so nearby.
人们认为，由永久性断层位移引起的微小“静态”应力变化能够改变附近断层发生地震的可能性或触发地震。许多近场触发研究，尤其是余震研究，将这些静态变化视为触发因素，并且仅从断层上施加荷载的等效变化角度来考虑它们。在此，我们报告了矩震级Mw = 7.3的兰德斯地震余震模式的比较情况，不仅与静态应力变化进行了比较，还与作为地震波传播的瞬态振荡应力变化（即“动态”应力）进行了比较。动态应力不会永久改变施加的荷载，因此只能通过改变断层带的力学状态或性质来触发地震。这些因动态作用而弱化的断层可能在地震波通过后发生破裂，甚至可能引发原本不会发生的地震。我们在余震和动态应力模式中发现了类似的不对称性，后者是由破裂传播导致的，而静态应力变化则不存在这种不对称性。先前的研究表明，动态应力能够在远距离促进破裂，但在此我们表明它们在近距离也能如此。
