image: Upper: A cross-section view of a subduction zone just after an earthquake on the plate boundary. Tensile stress is coseismically induced in the plates.
Lower: A few years after the earthquake. Post-seismic displacements of land are significant due to the upwelling flow of the uppermost mantle induced by the earthquake. After Sun et al. (2014 Nature).
Credit: Tomohiro Ohuchi
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Geodetic observations reveal that the deformation of the crust and upper mantle after a great earthquake continues for decades (Fig. 1). Viscosities of the upper mantle estimated from early post-seismic deformation are often significantly low (1017−1018 Pa·s) just after the earthquake then continuously increase to a typical value of ~1020 Pa·s with the passage of time. This characteristic of post-seismic mantle flow cannot be explained by partial melting (nor water weakening) of upper mantle rocks. We performed small-strain deformation experiments on natural olivine, which is the major mineral in the upper mantle, via a state-of-the-art large-volume deformation apparatus (multianvil apparatus) combined with high-flux synchrotron X-ray observations. We have successfully shown that the reported time-dependent crustal deformation, which continues for decades after a great earthquake, is explained by the transient creep of olivine (Fig. 2). |
Journal
Geophysical Research Letters