Direct Evidence for Thermal Pressurization in Experimental Faults
Abstract
The mechanical response of water-saturated experimental faults is controlled by the permeability of the host rock. We observe dynamic weakening by thermal pressurization of pore fluids in experimental faults under elevated confining pressure in the laboratory, using a rotary-shear apparatus with independent confining pressure and pore fluid pressure systems. Samples with saw-cut surfaces of Frederick diabase are tested under effective normal stress of 25-50 MPa and effective confining pressure of 20-49 MPa. Permeability of the samples is controlled by heat-treatment before each experiment, while frictional response is tested by velocity step experiments, where fault sliding velocity is changed from 3 μm/s to 2.5 mm/s. Our results show that: (1) the experimental faults weaken by thermal pressurization, as no other weakening mechanism is activated at the tested velocities at dry conditions; (2) the magnitude of the stress drops and rate of weakening increase as sample permeability decreases; and (3) the rate of re-strengthening of the faults, after the fault resumes sliding at the slow slip rate, is greater for high permeability samples. These observations are all in agreement with the expected hydro-mechanical behavior of thermal pressurization from theory. This study represents the first definite proof that weakening due to thermal pressurization actually is observed in experiments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR42A..03B
- Keywords:
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- 5112 Microstructure;
- PHYSICAL PROPERTIES OF ROCKS;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 8034 Rheology and friction of fault zones;
- STRUCTURAL GEOLOGY;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS