A new regime of slab-mantle coupling at the plate interface and its possible implications for the distribution of volcanoes

We investigate the effects of a thin, low viscosity layer just above the subducting slab on 3D thermal and flow structure in the mantle wedge by taking Northeast Japan as an example. The low viscosity layer assumed here is needed to explain the observed low surface heat flow and low seismic attenuation in the forearc by decoupling the mantle from the subducting slab. We find that when the viscosity in the low viscosity layer is sufficiently low, along-arc component of the flow arises inside the layer and produces along-arc temperature variation. It can also be considered as the along-arc changes in the degree of slab-mantle coupling at the plate interface. The onset time and the characteristic wavelength of the 3D flow depend on the viscosity and the extent of the low viscosity layer. In order to explain the observed spatial and temporal changes in the distribution of Quaternary volcanoes in Northeast Japan, the viscosity and the thickness of the low viscosity layer need to be