日本地球惑星科学連合2016年大会

講演情報

インターナショナルセッション(ポスター発表)

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG20] Intermediate-depth and deep earthquakes

2016年5月24日(火) 17:15 〜 18:30 ポスター会場 (国際展示場 6ホール)

コンビーナ:*久家 慶子(京都大学大学院理学研究科地球惑星科学専攻地球物理学教室)、北 佐枝子(国立研究開発法人 防災科学技術研究所)、Schubnel Alexandre(CNRS)、Abers Geoffrey(Cornell University, Department of Earth and Atmospheric Sciences, New York, USA)

17:15 〜 18:30

[SCG20-P09] The mechanics of intermediate and deep focus earthquakes: experimental evidences

*Alexandre Schubnel1Nadège Hilairet2Thomas Ferrand1Sarah Incel1Julien Gasc8Loic Labrousse7Fabrice Brunet6Joerg Renner3Harry W. Green5Yanbin Wang4 (1.Laboratoire de géologie, Ecole Normale Supérieure, Paris, France、2.UMET, U. Lille, France、3.Ruhr Universität Bochum, Germany、4.GSECARS, University of Chicago, USA、5.UC Riverside, USA、6.Isterre, U. Joseph Fourier, Grenoble, France、7.ISTEP, UPMC, Paris, France、8.Geosciences Montpellier, France)

キーワード:Phase transformation, Acoustic emission, rheology

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 2-4GPa, 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. In all these three cases, various post-mortem microstructural observations techniques (SEM, TEM, Raman, Microprobe, X-ray tomography) reveals that samples deformed under stress almost systematically present high presure (HP) faulting, to the contrary of samples transformed under isostatic conditions. In addition, AEs correspond to acoustic waves radiated by dynamic HP transformational faulting and follow the Gutenberg-Richter law over sometimes more than 4 orders of moment magnitudes.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 the Earth mantle's transition zone.