Numerical model of fluid pressure solitary wave propagation along the decollement of an accretionary wedge: application to the Nankai wedge
Résumé
Fluid pressure variations in time are thought to influence fault slip. Solitary (self-similar) pressure waves are one process by which a step pressure increase may be transmitted along a fault zone. Hypothetically, solitary wave propagation could be coupled with silent slip. Here we present a two-dimensional model of solitary wave propagation along a low-angle fault, scaled to a case example from Nankai accretionary wedge, and examine model sensitivity to décollement permeability. This model takes into account the effect of leakage out of the fault zone and pore pressure diffusion into the surrounding medium. We show that the propagation of a pore pressure wave along the décollement requires a permeability contrast between the dilated décollement (after the step pressure increase) and the surrounding material higher than 104. Wave velocity spans a wide range, from a few cm year−1 to more than 1 km year−1 for dilated décollement permeabilities of 10−15-10−12 m2. At the lower end of this range, the velocity of the pressure wave is comparable with the rate of accretion and the process of décollement propagation may be considered as a particular case of solitary wave propagation. At the upper end of the permeability range, a hypothetical pressure surge initiated after a subduction earthquake could reach the deformation front in a few tens of years. However, it seems unlikely that solitary pressure waves driven by flow along a décollement could explain silent slip events propagating at several km day−1