Narteau Clément, Byrdina Svetlana, Shebalin Peter, Schorlemmer Danijel
Institut de Physique du Globe de Paris (UMR 7154, CNRS, Univ. P7), 4 Place Jussieu, 75252 Paris Cedex 05, France.
Nature. 2009 Dec 3;462(7273):642-5. doi: 10.1038/nature08553.
Two of the long-standing relationships of statistical seismology are power laws: the Gutenberg-Richter relation describing the earthquake frequency-magnitude distribution, and the Omori-Utsu law characterizing the temporal decay of aftershock rate following a main shock. Recently, the effect of stress on the slope (the b value) of the earthquake frequency-magnitude distribution was determined by investigations of the faulting-style dependence of the b value. In a similar manner, we study here aftershock sequences according to the faulting style of their main shocks. We show that the time delay before the onset of the power-law aftershock decay rate (the c value) is on average shorter for thrust main shocks than for normal fault earthquakes, taking intermediate values for strike-slip events. These similar dependences on the faulting style indicate that both of the fundamental power laws are governed by the state of stress. Focal mechanisms are known for only 2 per cent of aftershocks. Therefore, c and b values are independent estimates and can be used as new tools to infer the stress field, which remains difficult to measure directly.
描述地震频率 - 震级分布的古登堡 - 里希特关系，以及表征主震后余震率随时间衰减的大森 - 宇津定律。最近，通过对b值的断层类型依赖性研究，确定了应力对地震频率 - 震级分布斜率（b值）的影响。以类似的方式，我们在此根据主震的断层类型研究余震序列。我们表明，逆冲主震的幂律余震衰减率开始前的时间延迟（c值）平均比正断层地震短，走滑事件的时间延迟取中间值。这些对断层类型的相似依赖性表明，这两个基本幂律均受应力状态控制。仅2%的余震有震源机制信息。因此，c值和b值是独立的估计值，可作为推断应力场的新工具，而应力场直接测量仍很困难。
