Earth Planets Space, Vol. 54 (No. 11), pp. 1173-1179, 2002
Stephen A. Miller
Geophysics Institute, ETH-Zurich 8093 Switzerland
(Received January 4, 2002; Revised September 8, 2002; Accepted September 9, 2002)
Abstract: The strength of seismogenic faults is fundamental to earthquake mechanics and plate tectonics, affecting many subsidiary processes in the solid earth. The key to understanding fault strength is determining the pore pressures and hydraulic properties within the faults and surrounding crust. The debate has lasted over decades, with evidence provided for both strong fault and weak fault scenarios. A recently proposed hypothesis for quantifying the strength at which faults fail uses earthquake scaling arguments to show that earthquakes fail over a range of strengths in the upper 15-20 km, and at near-lithostatic pore pressure below this depth. This observation, if correct, has important implications for crustal hydraulics, plate tectonics, and earthquake hazard assessment. This paper summarizes the arguments for high pore pressure faulting, and explores its implications for earthquake stress drops, strength of the lithosphere, and earthquake scaling. The hope is to establish a general framework for quantifying the role of fluids in the earthquake process, and to demonstrate that high fluid pressure may dominate failure of the brittle crust.