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High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus
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High-pressure mechanical instability in rocks
Science (New York, N.Y.)
|May 9, 1969
Summary
At low pressures, rocks deform without instability. However, at high pressures (7-10 kilobars), certain rocks exhibit unstable faulting, potentially explaining deep earthquakes.
Area of Science:
- Geophysics
- Rock Mechanics
- Seismology
Background:
- Sedimentary, altered mafic, porous volcanic rocks, and sand typically deform ductilely at low confining pressures.
- Ductile deformation is characterized by the absence of instabilities like audible elastic shocks.
Purpose of the Study:
- To investigate the deformation behavior of various rock types at high confining pressures.
- To determine if high-pressure conditions can induce unstable faulting and stick-slip behavior.
Main Methods:
- Experimental deformation of rock samples at confining pressures ranging from a few kilobars to 7-10 kilobars.
- Observation of deformation modes, focusing on the presence or absence of instabilities.
Main Results:
- At low confining pressures, deformation was ductile across all tested rock types.
- At pressures between 7 and 10 kilobars, unstable faulting and stick-slip behavior were observed in specific rock samples.
- This transition from ductile to unstable deformation was pressure-dependent.
Conclusions:
- High confining pressures can induce brittle failure mechanisms, such as unstable faulting, in rocks that deform ductilely at lower pressures.
- This high-pressure, low-temperature instability may be a key mechanism responsible for earthquakes occurring in deeply buried geological formations.
- Understanding these pressure-dependent transitions is crucial for seismic hazard assessment in deep crustal environments.
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