"Fault Friction at Seismic Slip Rates"
by Dr. John Platt (Carnegie Institute of Washington)

Abstract:

High-velocity friction experiments performed on natural fault materials show a large drop in strength at seismic slip velocities. These experiments support geophysical observations such as the low driving stress resolved on the San Andreas Fault that suggest mature faults weaken dramatically during seismic slip. However, while many coseismic weakening mechanisms have been proposed, it is still unclear which mechanisms are most important or how the efficiency of weakening depends on variables such as slip rate, temperature and pore pressure. My research uses mechanical models to investigate coseismic weakening, focusing in particular on the interplay between different weakening mechanisms and the constraints provided by laboratory, field and seismic data. To begin I show how different weakening mechanisms combine to drive coseismic strain localization and propagate a rupture. Next I present the results of recent high-velocity friction experiments that provide much tighter bounds on coseismic weakening than previously achieved and demonstrate how these experiments allow us to predict how the efficiency of coseismic weakening varies within the seismogenic zone. Finally I model how the heat generated during seismic slip influences the early stages of postseismic deformation, showing that enhanced ductile flow immediately following seismic slip can provide enough deformation to produce a near-total postseismic stress drop and a non-negligible tsunami hazard.