Figure 2

Undrained poroelastic response as a coseismic weakening mechanism. With the simulation setup of Fig. 1, we illustrate the influence of pore pressure response on rupture propagation speed. (a) Snapshot of coseismic pore pressure changes and contours of shear stress during rupture propagation. The reference pressure state, \(p_0\), is computed right before nucleation. Fast fault slip propagation leads to a pattern of compressions and extensions that induce sudden changes in pore pressure around the fault (red, increases; green, decreases). (b) Undrained pressure changes are particularly strong and sharp at the rupture tip, as revealed by the profiles of pore overpressure (solid black line) and accumulated slip (dotted red line) along one side of the fault. The undrained overpressure at the detachment front, \(\Delta P\), remains nearly constant over time (inset of b). (c,d) To highlight the impact of undrained response on earthquake rupture speed, we show the effect of changing Biot’s coefficient on the type of rupture propagation, while keeping the other parameters constant. In the case of \(\alpha _B\) \(=\) 0 (d), which neglects poroelastic coupling, rupture is symmetric and sub-Rayleigh, whereas for \(\alpha _B\) \(=\) 0.95 (c), the ensuing rupture is asymmetric, with one of the edges propagating at supershear speed.