The mechanics of intermediate and deep focus earthquakes
Event details
| Date | 18.03.2016 |
| Hour | 12:15 › 13:15 |
| Speaker | Prof. Dr Alexandre Schubnel, Associate Researcher at CNRS and Associate Professor at ENS, Paris, France |
| Location | |
| Category | Conferences - Seminars |
At least part of the subducting slab seismic activity could be triggered by phase transformations and mineral reactions. However, the way mineral reactions can modify the deformation regime of deep rocks, from ductile to brittle (embrittlement) is still poorly understood and remains one of the outstanding unsolved problems of geophysics and rock mechanics.
Here, we provide experimental evidence that, under differential stress at high pressure and temperature conditions (3-5GPa/800-1000°C), shear fractures nucleate and propagate at the onset of the olivine -> spinel transition in the Mg2GeO4 analogue system. The propagation of these fractures is sufficiently rapid to radiate energy in the form of intense acoustic emissions (AEs). Using a similar set-up, a second set of experiments demonstrates that glaucophane and lawsonite mixtures, two of the principal mineral water carriers in the subducted oceanic crust, undergo dynamic fracture instabilities when deformed within the eclogite field (3GPa/400-800°C). This time, AEs are observed due respectively to the glaucophane breakdown into jadeite and talc under low temperature and lawsonite dehydration under higher temperature. Finally, deformation experiments performed on partially serpentinized peridotites at 2-4 GPa, 500-700°C, demonstrate that 5% serpentine in sufficient to trigger dehydration embrittlement of the peridotite body. In this case, low serpentine contents may favor initiation of mechanical failure of the olivine “load bearing” network.
Put together, our observations provide strong experimental evidence of the role played by mineral reactions on earthquake triggering in mantle conditions, both in the Wadati-Benioff double plane of seismicity and in the Earth mantle's transition zone.
(full abstract as pdf available on memento)
Bio : Alexandre Schubnel has a double appointment:
1) as an associate researcher at the Centre National de la Recherche Scientifique, and
2) as an associate professor at the Laboratoire de Géologie of Ecole Normale Supérieure in Paris, France. His research interests lie in experimental Rock Physics and Earthquake Mechanics. In 2014, Alexandre Schubnel was awarded the bronze medal of CNRS and the Gouilloud-Schlumberger award of the French National Academy of Sciences for his work on “laboratory earthquakes"The mechanics of intermediate and deep focus earthquakes
Here, we provide experimental evidence that, under differential stress at high pressure and temperature conditions (3-5GPa/800-1000°C), shear fractures nucleate and propagate at the onset of the olivine -> spinel transition in the Mg2GeO4 analogue system. The propagation of these fractures is sufficiently rapid to radiate energy in the form of intense acoustic emissions (AEs). Using a similar set-up, a second set of experiments demonstrates that glaucophane and lawsonite mixtures, two of the principal mineral water carriers in the subducted oceanic crust, undergo dynamic fracture instabilities when deformed within the eclogite field (3GPa/400-800°C). This time, AEs are observed due respectively to the glaucophane breakdown into jadeite and talc under low temperature and lawsonite dehydration under higher temperature. Finally, deformation experiments performed on partially serpentinized peridotites at 2-4 GPa, 500-700°C, demonstrate that 5% serpentine in sufficient to trigger dehydration embrittlement of the peridotite body. In this case, low serpentine contents may favor initiation of mechanical failure of the olivine “load bearing” network.
Put together, our observations provide strong experimental evidence of the role played by mineral reactions on earthquake triggering in mantle conditions, both in the Wadati-Benioff double plane of seismicity and in the Earth mantle's transition zone.
(full abstract as pdf available on memento)
Bio : Alexandre Schubnel has a double appointment:
1) as an associate researcher at the Centre National de la Recherche Scientifique, and
2) as an associate professor at the Laboratoire de Géologie of Ecole Normale Supérieure in Paris, France. His research interests lie in experimental Rock Physics and Earthquake Mechanics. In 2014, Alexandre Schubnel was awarded the bronze medal of CNRS and the Gouilloud-Schlumberger award of the French National Academy of Sciences for his work on “laboratory earthquakes"The mechanics of intermediate and deep focus earthquakes
Practical information
- General public
- Free
Organizer
- Prof. Dr Brice Lecampion & Prof. Dr Katrin Beyer
Contact
- Prof. Dr Marie Violay