Progressive pulverization of fault rocks along active faults
Abstract
An unusual kind of damage has been observed recently along active faults. Finely pulverized rocks has been observed as far as 400m from the fault cores of active faults (Dor et al, 2006), in locations where damage is usually localized along a few macroscopic fractures. During previous high strain rate experiments, we have shown that strain localization is inhibited at strain rate higher than 100/s (Doan and Gary, 2009). This mechanism may explain the formation of pulverized rocks by a supershear rupture, or by a sharp Weertman pulse. Pulverization is an extensive damage that contributes to the energy balance of the earthquake that induced it. One poorly known component of the energy balance is the fracture energy. In case the pulverization of rocks is due to a single earthquake, fracture energy becomes very large. It is therefore important to assess whether pulverization are rather the product of a single earthquake or of multiple earthquakes. We made another series of experiments to assess the evolution of the transition of pulverization with the initial damage of the sample. We found that less damaged rocks induced an increase in strength (50MPa to 100MPa) and in the transition strain rate to pulverization (100/s to 250/s). It is therefore easier to re-pulverize rocks that are pulverized. We propose to feed this data to the model by Hild and Denoual (2002) to calibrate the transition from single fracturing to multiple fragmentation to estimate (1) the path of strain rate transition with time pulverization (2) the evolution of the grain size near active fault and try to compare with field observations along the San Andreas Fault.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T54A..03D
- Keywords:
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- 7209 SEISMOLOGY / Earthquake dynamics;
- 8004 STRUCTURAL GEOLOGY / Dynamics and mechanics of faulting;
- 8123 TECTONOPHYSICS / Dynamics: seismotectonics;
- 8163 TECTONOPHYSICS / Rheology and friction of fault zones