The role of thermal pressurization and dilatancy in controlling the rate of fault slip

Paul Segall, & Andrew M. Bradley

Published 2012, SCEC Contribution #1550

Geophysical observations have shown that transient slow slip events, with average slip speeds $v$ on the order of $10^{-8}$ to $10^{-7}$ m/s, occur in some subduction zones. These slip events occur on the same faults but at greater depth than large earthquakes (with slip speeds of order $\sim 1$ m/s). We explore the hypothesis that whether slip is slow or fast depends on the competition between dilatancy, which decreases fault zone pore pressure $p$, and thermal pressurization, which increases $p$. Shear resistance to slip is assumed to follow an effective stress law $\tau = f(\sigma-p) \equiv f \bar\sigma$. We present two-dimensional quasi-dynamic simulations that include rate-state friction, dilatancy, and heat and pore fluid flow normal to the fault. We find that at lower background effective normal stress ($\bar\sigma$), slow slip events occur spontaneously, whereas at higher $\bar\sigma$, slip is inertially limited. At intermediate $\bar\sigma$, dynamic events are followed by quiescent periods, and then long durations of repeating slow slip events. In these cases, accelerating slow events ultimately nucleate dynamic rupture. Zero-width shear zone approximations are adequate for slow slip events, but substantially overestimate the pore pressure and temperature changes during fast slip when dilatancy is included.

Citation
Segall, P., & Bradley, A. M. (2012). The role of thermal pressurization and dilatancy in controlling the rate of fault slip. Journal of Applied Mechanics, 79 (3). doi: 10.1115/1.4005896.