Earthquake physics
I'm studying the effects of the co-seismic temperature increases and shear heating on fault friction and the overall energy release during earthquakes. I develop numerical models of fault heating that take into account 1-D conductive heat transfer, and realistic variations in the slip velocity along the fault as schematically illustrated in this Figure.
It appears that the along-fault temperature distribution is controlled by a single parameter, the ratio of the fault thickness to the width of the conductive thermal boundary layer. For "thick" cracks, or at early stages of rupture, the local temperature on the fault surface is directly proportional to the amount of slip. For "thin" faults, or at later times, the temperature maximum shifts toward the crack tip. For faults having slip zone thickness of the order of centimeters or less, the onset of thermally-induced phenomena (e.g., frictional melting, thermal pressurization, etc.) may occur at any point along the rupture, depending on the degree of slip localization, and rupture duration. An example of the modeled temperature distribution due the to fault slip is shown below.
In the absence of significant increases in the pore fluid pressure, localized fault slip may raise temperature by several hundred degrees, sufficient to cause melting. The onset of frictional melting may give rise to substantial increases in the effective fault strength due to an increase in the effective fault contact area, and high viscosity of silicate melts near solidus. The inferred transient increases in the dynamic friction (``viscous braking'') are consistent with results of high-speed rock sliding experiments, and might explain field observations of the fault wall rip-out structures associated with pseudotachylites. Possible effects of viscous braking on the earthquake rupture dynamics include 1) de-localization of slip and increases in the effective fracture energy, 2) transition from a crack-like to a pulse-like rupture propagation, or 3) ultimate rupture arrest.
For more details, see these papers:
- Fialko, Y., Temperature fields generated by the elastodynamic propagation of shear cracks in the Earth (download PDF)
- Fialko, Y., and Y. Khazan, Fusion by earthquake fault friction: Stick or slip? (download PDF)
- Rock friction at high slip rates: "Melt Welt" mechanism of strong dynamic weakening in gabbro