Switching from seismic faulting to silent slips in harzburgite induced by H 2 O fluid at upper mantle pressures
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(2020) 175:79
ORIGINAL PAPER
Switching from seismic faulting to silent slips in harzburgite induced by H2O fluid at upper mantle pressures T. Ohuchi1 · X. Lei2 · Y. Higo3 · Y. Tange3 · T. Sakai1 Received: 11 February 2020 / Accepted: 16 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Slow-slip events frequently occur, but regular earthquakes are much less active on the H2O fluid-rich subduction interface at depths of ~ 40 km. The characteristic duration for silent earthquakes, which are categorized as the great slow-slip events, is more than five orders of magnitude longer than that for regular earthquakes. Such phenomena are often attributed to the slippage of the softer part of the subduction interface, but the impact of H 2O fluid on aseismic slip is still unsolved. Here, we conduct deformation experiments on water-saturated harzburgite at pressures of 1.2 to 3.0 GPa and temperatures of 770 to 1250 K, corresponding to the conditions of the lower part of the overriding plate just above the subduction interface. We observe deformation of the harzburgite followed by silent faulting at a significantly low stress level down to 0.3 GPa under fluid-bearing conditions, even though many acoustic emissions are generated at the onset of faulting in fluid-free harzburgite. We find that the observed silent faulting is caused by the detachment of asperity contacts by high pore pressures and lubrication of the fault plane by a hydration reaction. We therefore propose that H 2O fluid may prevent the occurrence of regular intraslab earthquakes, but trigger silent earthquakes. Keywords Subduction interface · H2O fluid · Acoustic emission · Silent faulting · Talc · Intraslab earthquake · Silent earthquake · Slow-slip events
Introduction Intraslab earthquakes occurring at depths greater than 40 km form the double seismic zones in many subducting slabs. The seismic zones roughly coincide with the temperature field for the stability limit of hydrous minerals such as antigorite. The dehydration reaction is much faster to maintain fluid-rich zones in/above the slabs (e.g., Chollet et al. 2011). Communicated by Hans Keppler. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00410-020-01716-x) contains supplementary material, which is available to authorized users. * T. Ohuchi [email protected]‑u.ac.jp 1
Geodynamics Research Center, Ehime University, Matsuyama 790‑8577, Japan
2
Geological Survey of Japan, National Institute for Advanced Industrial Science and Technology, Tsukuba 305‑8567, Japan
3
Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679‑5198, Japan
The relationship between regular intraslab earthquakes and H2O fluid is still not straightforward, although some seismological observations have pointed out that the existence of fluid channels in the slab may facilitate the genesis of earthquakes (Nakajima and Uchida 2018; Shiina et al. 2017) based on the concept of dehydration embrittlement (Raleigh and Paterson
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