Faults slip relaxes lithospheric stress imposed by mantle flow and in turn transfers stress to the ductile regions. The interplay of these systems governs the style of deformation at plate boundaries including the recurrence of seismic events. However, such deep processes remain challenging to incorporate in numerical simulations of earthquake cycles. Here we propose a model that couples fault slip and viscoelastic deformation to simulate fault dynamics in the lithosphere‐asthenosphere system. Our method resolves all phases of the earthquake cycle, including dynamic rupture propagation, afterslip, slow‐slip events, and the modulation of strain rate incurred in the ductile regions. Transient strain accelerations in the asthenosphere may follow both earthquakes and slow‐slip events shortly after the rupture, depending on the rheology of the upper mantle and the magnitude of the event. This study opens the door to greater insight into the variability of earthquake cycles by incorporating the dynamics of distributed deformation.
The deformation of mantle and crustal rocks in response to stress plays a crucial role in the distribution of seismic and volcanic hazards, controlling tectonic processes ranging from continental drift to earthquake triggering. However, the spatial variation of these dynamic properties is poorly understood as they are difficult to measure. We exploited the large stress perturbation incurred by the 2016 earthquake sequence in Kumamoto, Japan, to directly image localized and distributed deformation. The earthquakes illuminated distinct regions of low effective viscosity in the lower crust, notably beneath the Mount Aso and Mount Kuju volcanoes, surrounded by larger-scale variations of viscosity across the back-arc. This study demonstrates a new potential for geodesy to directly probe rock rheology in situ across many spatial and temporal scales.
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