A laboratory nanoseismological study on deep-focus earthquake micromechanics [electronic resource].

Published:: Washington, D.C. : United States. Dept. of Energy. Office of Science, 2017.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
Physical Description:: Article numbers e1,601,896 : digital, PDF file
Additional Creators:: University of Chicago, United States. Department of Energy. Office of Science, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

Global earthquake occurring rate displays an exponential decay down to ~300 km and then peaks around 550 to 600 km before terminating abruptly near 700 km. How fractures initiate, nucleate, and propagate at these depths remains one of the greatest puzzles in earth science, as increasing pressure inhibits fracture propagation. We report nanoseismological analysis on high-resolution acoustic emission (AE) records obtained during ruptures triggered by partial transformation from olivine to spinel in Mg₂GeO₄, an analog to the dominant mineral (Mg,Fe)₂SiO₄ olivine in the upper mantle, using state-of-the-art seismological techniques, in the laboratory. AEs’ focal mechanisms, as well as their distribution in both space and time during deformation, are carefully analyzed. Microstructure analysis shows that AEs are produced by the dynamic propagation of shear bands consisting of nanograined spinel. These nanoshear bands have a near constant thickness (~100 nm) but varying lengths and self-organize during deformation. This precursory seismic process leads to ultimate macroscopic failure of the samples. Several source parameters of AE events were extracted from the recorded waveforms, allowing close tracking of event initiation, clustering, and propagation throughout the deformation/transformation process. AEs follow the Gutenberg-Richter statistics with a well-defined b value of 1.5 over three orders of moment magnitudes, suggesting that laboratory failure processes are self-affine. The seismic relation between magnitude and rupture area correctly predicts AE magnitude at millimeter scales. A rupture propagation model based on strain localization theory is proposed. Future numerical analyses may help resolve scaling issues between laboratory AE events and deep-focus earthquakes.

Report Numbers:

E 1.99:1424023

Subject(s):

Geosciences

Note:

Published through SciTech Connect.
07/21/2017.
Science Advances 3 7 ISSN 2375-2548 AM
Yanbin Wang; Lupei Zhu; Feng Shi; Alexandre Schubnel; Nadege Hilairet; Tony Yu; Mark Rivers; Julien Gasc; Ahmed Addad; Damien Deldicque; Ziyu Li; Fabrice Brunet.

Funding Information:

FG02-94ER14466
AC02-06CH11357

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