Abstract
Slow-slip events are earthquake-like events only with much lower slip rates. While peak coseismic velocities can reach tens of meters per second, slow-slip is on the order of 10−7±2 m/s and may last for days to weeks. Under the rate-and-state model of fault friction, slow-slip is produced only when the asperity size is commensurate with the critical nucleation size, a function of frictional properties. However, it is unlikely that all subduction zones embody the same frictional properties. In addition to friction, plastic flow of antigorite-rich serpentinite may significantly influence the dynamics of fault slip near the mantle wedge corner. Here, we show that the range of frictional parameters that generate slow slip is widened in the presence of a serpentinized layer along the subduction plate interface. We observe increased stability and damping of fast ruptures in a semi-brittle fault zone governed by both brittle and viscoelastic constitutive response. The rate of viscous serpentinite flow, governed by dislocation creep, is enhanced by high ambient temperatures. When effective viscosity is taken to be dynamic, long-term slow slip events spontaneously emerge. Integration of rheology, thermal effects, and other microphysical processes with rate-and-state friction may yield further insight into the phenomenology of slow slip.
Highlights
Slow-slip events are earthquake-like events only with much lower slip rates
We evaluate the resulting dynamics of fault slip for 30 years, representing about
Following our concern about the role of shear heating, we evaluate the dynamics of temperature and resulting effective viscosities in the fault zones for both models (Fig. 5)
Summary
Where A is a reference strain rate, n is the dislocation creep exponent, Q is the activation energy, p is confining pressure, V is the activation volume, R is the ideal gas constant, and T is temperature. The serpentinite effective viscosity η = τ/ε obeys an Arrhenius-style activation law with a low activation energy, and even at the 300–500 °C temperatures of subduction zones, viscous flow can be significant and play a nontrivial role in the dynamics of fault slip. A set of frictional parameters that would have caused a fast rupture could instead result in a slow-slip event when viscous flow is activated. Even though serpentinite has a small activation energy of Q = 13.3 kJ/ mol[38], the potentially high dynamic range of temperature due to shear heating during fault slip may play an important role near the fault[61]. To test the importance of this effect in the dynamics of slow slip, we build a two-dimensional model of fault slip that includes shear heating and the diffusion of temperature away from the fault[62]. We evaluate the resulting dynamics of fault slip for 30 years, representing about
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