Seismic evidence for thermal runaway during intermediate‐depth earthquake rupture

Abstract

[1] Intermediate-depth earthquakes occur at depths where temperatures and pressures exceed those at which brittle failure is expected. There are two leading candidates for the physical mechanism behind these earthquakes: dehydration embrittlement and self-localizing thermal shear runaway. A complete energy budget for a range of earthquake sizes can help constrain whether either of these mechanisms might play a role in intermediate-depth earthquake rupture. The combination of high stress drop and low radiation efficiency that we observe for M w 4-5 earthquakes in the Bucaramanga Nest implies a temperature increase of 600-1000°C for a centimeter-scale layer during earthquake failure. This suggests that substantial shear heating, and possibly partial melting, occurs during intermediate-depth earthquake failure. Our observations support thermal shear runaway as the mechanism for intermediate-depth earthquakes, which would help explain differences in their behavior compared to shallow earthquakes. Citation: Prieto, G. A., M. Florez, S. A. Barrett, and G. C. Beroza (2013), Seismic evidence for thermal runaway during intermediate-depth earthquake rupture, Geophys. Res. Lett., 40,[6064][6065][6066][6067][6068]

Large subduction earthquakes along the fossil Moho in Alpine Corsica

“…Theoretical investigations (Braeck and Podladchikov, 2007) and numerical simulations (John et al, 2009) of thermal runaway show that it requires lower differential stresses than frictional faulting at the ambient conditions of intermediate and deep earthquakes in the absence of a free fl uid. A recent seismological study of 253 intermediate-depth earthquakes recorded in the Andean subduction zone also support the suggestions that such earthquakes are triggered by a thermal runaway mechanism rather than by brittle faulting (Prieto et al, 2013).…”

Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle

“…The earthquake may have nucleated along one of these shear zones through a thermal shear runaway mechanism or aided by dehydration reactions, triggering the M W 4.8 earthquake and its only aftershock ( 12 , 27 , 28 ). The 1979 deep Randolph earthquake probably nucleated in a similar manner (see fig.…”

“…Estimates of the seismic radiation, the source dimension, and the amount of slip of an earthquake can be used to investigate the stress drop and fracture energy ( 12 ). We also perform detailed thermal modeling to ascertain whether the Wyoming earthquake occurred below or above the brittle-ductile transition temperature.…”

Shear heating-induced strain localization across the scales

“…However, stress estimations based on both natural observations and laboratory experiments agree that required stress levels are on the order of several hundreds of MPa [45] up to GPa [44]. Indirect confirmation of the occurrence of thermal runaway instabilities in the deep Earth has recently been provided by geophysical monitoring [46]. In general, shear heating is often invoked for the explanation of elevated temperatures experienced by rocks [47,48].…”