** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.

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    Research

    Solid earth sciences

    201510201510

    Can clay minerals account for the behavior of non-asperity on the subducting plate interface?

    Katayama I, Kubo T, Sakuma H, Kawai K

    Frictional healing, Clay minerals, Seismic asperity, Subducting plate interface

    Schematic model of the plate interface at a subduction zone. The clay-rich regions of the interface could be weakly coupled and act as non-asperity, whereas the unaltered patches remain strongly coupled and have the potential to generate megathrust earthquakes.

    Seismicity along the subducting plate interface shows regional variation, which has been explained by the seismic asperity model where large earthquakes occur at strongly coupled patches that are surrounded by weakly coupled regions. This suggests that the subduction plate interface is heterogeneous in terms of frictional properties; however, the mechanism producing the difference between strong and weak couplings remains poorly understood. Here, we propose that the heterogeneity of the fluid pathway and of the spatial distribution of clay minerals plays a key role in the formation of non-asperity at the subducting plate interface. We use laboratory measurements of frictional properties to show that clay minerals on a simulated fault interface are characterized by weak and slow recovery, whereas other materials such as quartz show relatively quick recovery and thereby strong coupling on the fault surface. Aqueous fluids change the mineralogy at the plate interface by producing clay minerals due to hydrate reactions, suggesting that the hydrated weakly coupled regions act as a non-asperity and form a barrier to rupture propagation along the plate boundary at the depths of seismogenic zone.