Modeling Seismic Cycles of Great Megathrust Earthquakes Across the Scales With Focus at Postseismic Phase

Abstract

Subduction is substantially multiscale process where the stresses are built by long‐term tectonic motions, modified by sudden jerky deformations during earthquakes, and then restored by following multiple relaxation processes. Here we develop a cross‐scale thermomechanical model aimed to simulate the subduction process from 1 min to million years' time scale. The model employs elasticity, nonlinear transient viscous rheology, and rate‐and‐state friction. It generates spontaneous earthquake sequences and by using an adaptive time step algorithm, recreates the deformation process as observed naturally during the seismic cycle and multiple seismic cycles. The model predicts that viscosity in the mantle wedge drops by more than three orders of magnitude during the great earthquake with a magnitude above 9. As a result, the surface velocities just an hour or day after the earthquake are controlled by viscoelastic relaxation in the several hundred km of mantle landward of the trench and not by the afterslip localized at the fault as is currently believed. Our model replicates centuries‐long seismic cycles exhibited by the greatest earthquakes and is consistent with the postseismic surface displacements recorded after the Great Tohoku Earthquake. We demonstrate that there is no contradiction between extremely low mechanical coupling at the subduction megathrust in South Chile inferred from long‐term geodynamic models and appearance of the largest earthquakes, like the Great Chile 1960 Earthquake.

Asthenosphere Flow Modulated by Megathrust Earthquake Cycles

“…In the oceanic plate, the temperature follows the cooling half-space model with a plate age of 2 × 10 15 s, that is, ∼60 Myr and a basal mantle temperature of 1673 K. I use the constitutive properties of wet olivine with with 1,000 ppm H/Si reported by Hirth and Kohlstedt (2003) and summarized in Table 1. The seismic cycle overprints a longer timescale tectonic deformation (Herrendörfer et al, 2015;Sobolev & Muldashev, 2017) that can only be crudely approximated in short-term simulations. For the sake of simplicity, I assume that viscoelastic flow is driven by a background shortening rate oḟ0 22 = −10 −15 /s.…”

An Invariant Rate‐ and State‐Dependent Friction Formulation for Viscoeastoplastic Earthquake Cycle Simulations

“…How important are large‐scale tectonic characteristics, which evolve over million years, for earthquakes and their properties. However, a modeling approach that incorporates all these challenging ingredients does not exist yet, despite solid attempts (Lapusta et al, ; Sobolev & Muldashev, ; van Dinther, Gerya, Dalguer, Corbi, et al, ; van Dinther, Gerya, Dalguer, Mai, et al, ).…”

Spatiotemporal Variation of Mantle Viscosity and the Presence of Cratonic Mantle Inferred From 8 Years of Postseismic Deformation Following the 2010 Maule, Chile, Earthquake

“…Temporally variable viscosities have also been inferred from geodetic time series of postseismic relaxation (e.g., Freed & Burgmann, 2004;Hussain et al, 2018;Malservisi et al, 2015;Pollitz et al, 2001). Another commonly used rheology, physics-based power law rheology, allows for a continuous increase of viscosity constrained by laboratory-scale empirical relationships of stress dependency (e.g., Freed & Burgmann, 2004;Kirby & Kronenberg, 1987;Sobolev & Muldashev, 2017). Another commonly used rheology, physics-based power law rheology, allows for a continuous increase of viscosity constrained by laboratory-scale empirical relationships of stress dependency (e.g., Freed & Burgmann, 2004;Kirby & Kronenberg, 1987;Sobolev & Muldashev, 2017).…”

“…A common and convenient approximation of the transient viscosity is the biviscous Burgers rheology, which allows for an initial short-term viscosity that transitions into a longer-term viscosity (e.g., Pollitz, 2003;Wang et al, 2012). Another commonly used rheology, physics-based power law rheology, allows for a continuous increase of viscosity constrained by laboratory-scale empirical relationships of stress dependency (e.g., Freed & Burgmann, 2004;Kirby & Kronenberg, 1987;Sobolev & Muldashev, 2017). These rheology models, though, include necessary simplifications or are based on empirical relationships.…”