Along-arc heterogeneous rheology inferred from post-seismic deformation of the 2011 Tohoku-oki earthquake

SUMMARY The Japan forearc plays a crucial role in modulating the post-seismic deformation in response to the enormous stress perturbation induced by the 2011 Tohoku-oki earthquake. Dense geodetic observations across Japan have revealed coupled interactions between afterslip on the subducting plate interface and viscous deformation within the mantle wedge, and detailed numerical models can provide further profound insights into the forearc rheology. Recent studies have revealed the presence of a stagnant section in the forearc mantle of the Tohoku subduction zone, and here we investigate the associated along-arc variation of the stagnant part of the mantle wedge (cold nose) across Japan. We utilize a newly deployed geodetic network along a corridor in the Fukushima–Niigata region and compare the surface deformation pattern to that of the Miyagi–Yamagata corridor close to the main rupture area. We present a 3-D rheological model using laboratory-derived constitutive laws to simulate the geodetic observations including displacement fields and their time-series. Our results suggest along-arc heterogeneity in the forearc mantle rheology; specifically, we find a narrower cold nose in the Miyagi region and a wider one in the Fukushima forearc. The geodetic inferences on the forearc variation are consistent with along-arc spatial heterogeneity in the cut-off depth for shallow earthquakes as well as comparative measurements of the respective geothermal gradients between the Miyagi and Fukushima regions.