Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Nature 642-U113 2009 fdi:010048437 ENG Nature 0028-0836 ISI:000272277900039 7273 10.1038/nature08553 https://www.documentation.ird.fr/hor/fdi:010048437 https://www.documentation.ird.fr/intranet/publi/2009/12/010048437.pdf 462 Horizon (IRD) Two of the long-standing relationships of statistical seismology are power laws: the Gutenberg-Richter relation(1) describing the earthquake frequency-magnitude distribution, and the Omori-Utsu law(2) 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(3) 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. 064 ou 066 UR157