Rapid mantle flow with power-law creep explains deformation after the 2011 Tohoku mega-quake

Abstract

The deformation transient following large subduction zone earthquakes is thought to originate from the interaction of viscoelastic flow in the asthenospheric mantle and slip on the megathrust that are both accelerated by the sudden coseismic stress change. Here, we show that combining insight from laboratory solid-state creep and friction experiments can successfully explain the spatial distribution of surface deformation in the first few years after the 2011 Mw 9.0 Tohoku-Oki earthquake. The transient reduction of effective viscosity resulting from dislocation creep in the asthenosphere explains the peculiar retrograde displacement revealed by seafloor geodesy, while the slip acceleration on the megathrust accounts for surface displacements on land and offshore outside the rupture area. Our results suggest that a rapid mantle flow takes place in the asthenosphere with temporarily decreased viscosity in response to large coseismic stress, presumably due to the activation of power-law creep during the post-earthquake period.

Quantitative relationship between aseismic slip propagation speed and frictional properties

“…As demonstrated by observations following the 2011 Tohoku earthquake, postseismic deformation is thought to be a combination of afterslip, viscoelastic relaxation (e.g., Sun et al, 2014;Agata et al, 2019) and poroelastic rebound (Barbot and Fialko, 2010). The contribution to transient deformation due to asthenosphere flow is predominant in the landward surface area (Barbot, 2018), depending on the rheology of the upper mantle and the magnitude of the event (Lambert and Barbot, 2016).…”

Focal Mechanisms of Deep Low‐Frequency Earthquakes Beneath Zao Volcano, Northeast Japan, and Relationship to the 2011 Tohoku Earthquake

“…For example, surface deformation continued for two years after the Tohoku earthquake and the postseismic displacement is best explained by a combination of afterslip and viscoelastic relaxation (Diao et al, ; Sun et al, ). As a result, viscoelastic deformation for 2.5 years induced by coseismic slip and afterslip of the Tohoku earthquake would be significantly larger than the coseismic or afterslip displacement around the Moho in the inland region (Agata et al, ; Yamagiwa et al, ). Hence, the viscoelastic relaxation is a reasonable model to explain the two‐year delay, although further quantitative assessment of the stress loading requires more complete understanding of LFEs as a physical process.…”

Omori-like slow decay (p < 1) of postseismic displacement rates following the 2011 Tohoku megathrust earthquake

“…The existence of a subducting slab and localized weaker zones have been suggested (Hu et al 2014(Hu et al , 2016Muto et al 2016;Freed et al 2017;Suito 2017). Furthermore, a stressdependent and non-constant viscosity due to power-law dislocation creep (Freed and Bürgmann 2004) has been implemented in recent studies (Sobolev and Muldashev 2017;Agata et al 2019), where a sophisticated study (Sobolev and Muldashev 2017) simulated ground displacement rates by varying the model parameters in a two-dimensional body. This behavior is intrinsic to giant earthquakes which mostly can occur only in subduction zones, because a giant earthquake has a huge effect on the viscosity due to the power-law of dislocation creep.…”

“…Seafloor geodetic observations of the 2011 Tohoku megathrust earthquake (moment magnitude (Mw) 9.0) provided clear evidence for viscoelastic relaxation as the dominant deformation mechanism (Sun et al 2014;Watanabe et al 2014). However, diverse postseismic deformation models that incorporate afterslip and viscoelastic relaxation have been proposed (Diao et al 2014;Yamagiwa et al 2015;Hu et al 2016;Muto et al 2016;Iinuma et al 2016;Freed et al 2017;Sobolev and Muldashev 2017;Suito 2017;Agata et al 2019), with the model results being strongly dependent on their structures, constitutive laws, and viscoelasticity parameters. Some studies assumed layered structures of parameters (Diao et al 2014;Yamagiwa et al 2015), some reduced to two-dimensional problems (Muto et al 2016;Sobolev and Muldashev 2017), but the others considered three-dimensional parameter distribution, with various constitutive laws such as the Maxwell viscosity, the bi-viscous Burgers rheology, or power-law rheology.…”