Transient rheology of the Sumatran mantle wedge revealed by a decade of great earthquakes

Understanding the rheological properties of the upper mantle is essential to develop a consistent model of mantle dynamics and plate tectonics. However, the spatial distribution and temporal evolution of these properties remain unclear. Here, we infer the rheological properties of the asthenosphere across multiple great megathrust earthquakes between 2004 and 2014 along the Sumatran subduction zone, taking advantage of decade-long continuous GPS and tide-gauge measurements. We observe transient mantle wedge flow following these earthquakes, and infer the temporal evolution of the effective viscosity. We show that the evolution of stress and strain rate following these earthquakes is better matched by a bi-viscous than by a power-law rheology model, and we estimate laterally heterogeneous transient and background viscosities on the order of ~10 17 and ~10 19 Pa s, respectively. Our results constitute a preliminary rheological model to explain stress evolution within earthquake cycles and the development of seismic hazard in the region. The rheology of the upper mantle is key to understanding how plate tectonics may evolve. Here, using GPS and tide-gauge measurements along the Sumatran subduction zone, the authors’ show that a bi-viscous rheology model is needed to explain the stress and strain evolution of the upper mantle following earthquakes.