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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 109,
B01303,
doi:10.1029/2003JB002497,
2004
Temperature fields generated by the elastodynamic propagation of shear cracks in the Earth
Yuri Fialko
Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La
Jolla, California, USA
Abstract
Thermal perturbations associated with seismic slip on faults may significantly affect the dynamic friction and the mechanical
energy release during earthquakes. This paper investigates details of the coseismic temperature increases associated with
the elastodynamic propagation of shear cracks and effects of fault heating on the dynamic fault strength. Self-similar solutions
are presented for the temperature evolution on a surface of a mode II shear crack and a self-healing pulse rupturing at a
constant velocity. The along-crack temperature distribution is controlled by a single parameter, the ratio of the crack thickness
to the width of the conductive thermal boundary layer, . For “thick” cracks, or at early stages of rupture ( > 1), the local temperature on the crack surface is directly proportional to the amount of slip. For “thin” cracks, or at
later times ( < 1), 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. 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) delocalization 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. Assuming that
the pulse-like ruptures heal by incipient fusion, the seismologic observations can be used to place a lower bound on the dynamic
fault friction. This bound is found to be of the order of several megapascals, essentially independent of the earthquake size.
Further experimental and theoretical studies of melt rheology at high strain rates are needed to quantify the effects of melting
on the dynamic fault strength.
Received 14
March
2003;
accepted 13
October
2003;
published 14
January
2004.
Index Terms: 3210 Mathematical Geophysics: Modeling; 5104 Physical Properties of Rocks: Fracture and flow; 7209 Seismology: Earthquake dynamics and mechanics; 7260 Seismology: Theory and modeling; 8010 Structural Geology: Fractures and faults.
Read Full Article (file size: 839479 bytes) Cited by
Citation: Fialko, Y.
(2004),
Temperature fields generated by the elastodynamic propagation of shear cracks in the Earth,
J. Geophys. Res.,
109,
B01303,
doi:10.1029/2003JB002497.
Copyright 2004 by the American Geophysical Union.
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