Numerical models for slip on the subduction interface motivated by field observations

Observations of ancient subduction fault zones, combined with mechanical models of the plate interface, indicate that many first-order features of shallow subduction seismicity can result from failure of areas of the interface that nucleate and strengthen during interseismic periods at rates determined by silica kinetics. In the Shimanto belt, Japan, and in the Kodiak archipelago in Alaska, shear zones of tectonic mélange were accreted at a range of depths representative of the seismogenic zone. The scaly fabric and crack-seal veins in these mélanges record fluctuations in crack porosity at rates controlled by silica kinetics. Temperature-dependent healing of cracks impacts the critical stiffness for slip stability through increases in contact area and contact junction strength-a macroscopic analogue to aging in slide-hold-slide experiments on gouge. The potential for portions of the interface to strengthen through mineral redistribution during the interseismic period forms the basis for a two-dimensional numerical block-slider model for slip behavior of the subduction interface, where aging follows a temperature-dependent rate law. The model responds to a population balance equation, with nucleation, strengthening, and failure of patches of the interface that have greater static frictional strength, defined in the model as "asperities." An exponential rate law for nucleation and strengthening, based on Arrhenius equation silica kinetics, leads to: (1) supercycles of buildup and release of elastic strain, (2) a temperature-based updip limit to genesis of large earthquakes, and (3) a power-law size distribution of earthquakes that varies as a function of temperature. Asperities in this case arise by stochastic nucleation and strengthening based on a temperature-dependent rate law and are unrelated to roughness of the plate interface. Over a temperature range typical of the seismogenic zone, variations in effective stress along the plate interface lead to heterogeneous frictional characteristics in the interseismic period that could control the location, recurrence time, and magnitude of earthquakes.