Coupled afterslip and transient mantle flow after the 2011 Tohoku earthquake

Abstract

Modeling of postseismic deformation following great earthquakes has revealed the viscous structure of the mantle and the frictional properties of the fault interface. However, for giant megathrust events, viscoelastic flow and afterslip mechanically interplay with each other during the postseismic period. We explore the role of afterslip and viscoelastic relaxation and their interaction in the aftermath of the 2011 Mw (moment magnitude) 9.0 Tohoku earthquake based on a detailed model analysis of the postseismic deformation with laterally varying, experimentally constrained, rock rheology. Mechanical coupling between viscoelastic relaxation and afterslip notably modifies both the afterslip distribution and surface deformation. Thus, we highlight the importance of addressing mechanical coupling for long-term studies of postseismic relaxation, especially in the context of the geodynamics of the Japan trench across the seismic cycle.

Backstress from dislocation interactions quantified by nanoindentation load-drop experiments

“…The transient rheology of the upper mantle is inferred to control the dynamics of many geologic phenomena, including post-seismic deformation (e.g., Freed et al, 2012;Wang et al, 2012;Hu et al, 2016;Qiu et al, 2018). Several studies have presented models to describe the transient rheological behavior following large earthquakes (e.g., Masuti et al, 2016;Moore et al, 2017;Muto et al, 2019), but the physical mechanism that gives rise to this complex time-dependent rheology is not well-constrained. For example, Masuti et al (2016) used a strain hardening coefficient to modify a stress element in their Burgers model, but noted that the functional form of the constitutive law was completely unknown.…”

Structural control and system-level behavior of the seismic cycle at the Nankai Trough

“…3a, 4f ). The afterslip period consists of a short pulse of rapidly decaying creep that lasts a few years, as observed after all suitably instrumented large subduction earthquakes (e.g., Hsu et al 2006;Chlieh 2007;Feng et al 2016;Tsang et al 2016;Bedford et al 2016;Klein et al 2016;Hu et al 2016;Qiu et al 2018;Tang et al 2019;Muto et al 2011).…”

“…In contrast to steady-state, the micro-mechanics of transient creep are poorly understood and different constitutive relationships have been proposed (Sherburn et al 2011;Thieme et al 2018;Holtzman et al 2018), but plastic anisotropy within single crystals may be an important factor (Masuti et al 2019). Because of the rapid change imposed by the seismic cycle, transient creep may be operating during postseismic relaxation (Pollitz et al 2008;Freed et al 2010;Hoechner et al 2011;Tang et al 2019;Muto et al 2011). The strain-rate of transient creep may be represented by an additional strain component (Masuti et al 2016) where A K is a pre-exponential factor, q = σ − 2G K ǫ K is the effective stress, and G K is strain-hardening coefficient.…”

“…The strain-rate of transient creep may be represented by an additional strain component (Masuti et al 2016) where A K is a pre-exponential factor, q = σ − 2G K ǫ K is the effective stress, and G K is strain-hardening coefficient. This rheological framework has been useful to model postseismic deformation (e.g., Nur and Mavko 1974;Savage 2000;Hirahara 2002;Freed and Bürgmann 2004;Hu et al 2004;Hetland and Hager 2005;Wang 2007;Pollitz et al 2008;Johnson et al 2009;Suito and Freymueller 2009;Wang et al 2012;Sun 2014;Hu et al 2016;Klein et al 2016;Muto et al 2011, and references therein). In this study, we approximate the rheological response by the steady-state, as the details of sub-annual evolution of viscoelastic relaxation is not of central importance to our discussion.…”

“…Asthenospheric flow is modulated by the seismic cycle (Barbot 2018b), creating large-scale deformation during the postseismic period (Savage and Prescott 1978;Hirahara 2002;Hu et al 2004;Wang 2007;Pollitz et al 2008;Wang et al 2012;Sun 2014;Masuti et al 2016;Klein et al 2016;Li et al 2018;Qiu et al 2018;Weiss et al 2019). Viscoelastic flow and fault slip are mechanically coupled during postseismic deformation (Agata et al 2019;Muto et al 2011). However, the impact of viscoelastic flow on the recurrence pattern of earthquakes and slow-slip events is poorly known.…”