Intermediate-depth earthquakes linked to localized heating in dunite and harzburgite

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The occurrence of intermediate-depth and deep earthquakes at depths greater than 60 km in subducting slabs has long puzzled geoscientists. These earthquakes require some mechanism to accelerate the fault movement at high pressures above 1.8 GPa. Localized heating would contribute to faulting, but experimental evidence for this mechanism has been limited to pressures of up to 0.5 GPa. Here we conduct deformation experiments on dry dunite samples at pressures of 1.0 to 2.6 GPa and temperatures of 860 to 1,350 K—conditions close to those for relatively shallow intermediate-depth earthquakes. We observe plastic deformation of the dunite, followed by faulting and acoustic emissions at an accelerated strain rate of about 5 × 10−5 s−1 or higher. We find that ultrafine-grained gouge layers containing iron-rich melt films, which is indicative of a very high peak temperature of about 2,110 K along the fault planes. We also observe faulting in wet harzburgite—a dehydration product of antigorite—at natural stress levels of 0.3 to 0.4 gigapascals. We therefore suggest that intermediate-depth earthquakes can be induced by localized heating both in dry and wet subducting slabs, if the background strain rate exceeds a threshold value in the range from 10−16 to 10−13 s−1.

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Figure 1: Mechanical and acoustic records in a dry dunite at 1,160 K.
Figure 2: Conditions for faulting.
Figure 3: Microstructures in a dry dunite (M1681).
Figure 4: Conditions for localized heating in harzburgite.
Figure 5: Faulting caused by accelerated strain localization in peridotites with and without a fine-grained shear zone.


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We thank T. Kubo for discussion. An official review by R. Farla improved the manuscript. This research was conducted under the approval of SPring-8 (Nos. 2015A0075, 2015B0075, and 2016A0075) and supported by the JSPS through Grant-in-Aid for Scientific Research (Nos. 25220712, 25707040 and 16H04077).

Author information

T.O. conceived the idea, conducted experiments, and wrote the manuscript. X.L. contributed to technical developments on the acoustic emissions measurement. H.O. took all the STEM micrographs. T.S. and K.F. contributed to TEM observations. Y.H. and Y.T. assisted in situ experiments. T.I. contributed to interpreting the results and writing the manuscript.

Correspondence to Tomohiro Ohuchi.

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Ohuchi, T., Lei, X., Ohfuji, H. et al. Intermediate-depth earthquakes linked to localized heating in dunite and harzburgite. Nature Geosci 10, 771–776 (2017) doi:10.1038/ngeo3011

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