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| Titel |
The role of gouge and temperature on flash heating and its hysteresis |
| VerfasserIn |
John Platt, Brooks Proctor, Thomas Mitchell, Greg Hirth, David Goldsby, Giulio Di Toro, Nick Beeler, Terry Tullis |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108056
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| Publikation (Nr.) |
 EGU/EGU2015-7787.pdf |
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| Zusammenfassung |
| Geophysical observations such as the low heat anomaly suggest that mature faults weaken
significantly during earthquakes. These observations are supported by high-velocity friction
experiments on natural samples that show dramatic weakening at typical seismic slip rates.
One proposed weakening mechanism is the breakdown of frictional contacts at a critical
weakening temperature, a process known as flash heating. For bare surface sliding Rice
[2006] showed that heat generation at frictional contacts triggers flash heating above a critical
weakening velocity V w of ~ 0.1 m/s. However, all faults generate a gouge layer at
least a few millimeters wide, and the efficiency of flash heating in gouge is still
unknown.
Building on Rempel [2006] and Beeler et al. [2008], we model flash heating in gouge by
assuming that the total slip rate applied across the deforming zone is shared between multiple
frictional contacts. Solving for the contact temperature we show that flash heating occurs
when the strain rate in the deforming gouge exceeds a critical weakening strain
rate controlled by the gouge properties, corresponding to the local slip rate at a
single contact reaching the critical weakening slip rate for bare surface sliding.
Our results show that the presence of a thin gouge layer dramatically reduces the
efficiency of flash heating, with the slip rates required to trigger flash heating at least an
order of magnitude greater than those predicted for bare surface sliding in Rice
[2006].
Having developed a model for flash heating during distributed shear, we next model the
weakening of a uniformly sheared gouge layer. We show that if flash heating is triggered then
the evolution of the bulk fault temperature leads to a near total strength drop in just a few
milliseconds, and use this insight to predict a slip weakening distance that is inversely
proportional to the normal stress. This dependence on normal stress is in good agreement
with data from high-velocity friction experiments, and of great importance when
extrapolating experimental results to seismogenic depths. In addition, we couple flash heating
with a model for thermal pressurization, allowing us to determine the dominant weakening
mechanism for a range of fault conditions. Our results show that flash heating is
likely unimportant at shallow depths where thermal pressurization dominates, but
becomes as important as thermal pressurization further down in the seismogenic
zone.
Finally, we link our model with the recent experimental results presented in Proctor et al.
[2014]. We show that the evolution of sliding surface temperature may explain some of the
hysteresis commonly seen in bare surface sliding experiments that trigger flash heating, with
higher friction observed during acceleration than deceleration. Our model gives excellent
agreement with the experimental data from Proctor et al. [2014] for both acceleration and
deceleration over a wide range of slip rates. Building on this we discuss the role of flash
heating near the trailing edge of a rupture where temperatures are high and slip is
decelerating. |
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