Rupture Reactivation during the 2011M_w 9.0 Tohoku Earthquake: Dynamic Rupture and Ground‐Motion Simulations

Abstract

Near-source ground-motion observations and kinematic source inversions suggest that the rupture process of the 2011 M w 9.0 Tohoku earthquake involved rupture reactivation, that is, repeated rupture nucleation in the same hypocentral area. This unusual phenomenon may have provided a second breath to the rupture that enhanced its final size. Here, we propose that rupture reactivation may have been governed by a slip-weakening friction model with two sequential strength drops, the second one being activated at large slip. Such frictional behavior has been previously observed in laboratory experiments and attributed to pressurization of fault-zone fluids by mineral decomposition reactions activated by shear heating, such as dehydration and decarbonation. Further evidence of this double-slip-weakening friction model is obtained here from the dynamic stress changes in the hypocentral region derived from a finite source inversion model. We incorporate this friction model in a dynamic rupture simulation comprising two main asperities constrained by source inversion models and several deep small asperities constrained by backprojection source imaging studies. Our simulation produces ground-motion patterns along the Japanese coast consistent with observations and rupture patterns consistent with a kinematic source model featuring rupture reactivation. The deep small asperities serve as a bridge to connect the two main asperities, and the rupture reactivation mechanism is needed to reproduce the observed ground-motion pattern. Therefore, we argue that rupture reactivation during the 2011 Tohoku earthquake is consistent with a second strength drop, possibly caused by activation of thermochemical weakening processes at large slip.Online Material: Movie of simulated rupture and wave propagation and ground velocities recorded at the KiK-net and K-NET seismic networks.

The 2016 Kaikōura Earthquake Revealed by Kinematic Source Inversion and Seismic Wavefield Simulations: Slow Rupture Propagation on a Geometrically Complex Crustal Fault Network

“…Model A suggests that the second and main asperity overlaps the first one by 40%; Model B suggests that the second and main asperity totally overlaps the first one. Rerupturing of major asperities (or rupture reactivation) has been previously inferred for the 2011 M9.0 Tohoku-Oki earthquake from a kinematic source model (Lee et al, 2011) as well as a dynamic rupture model (Galvez et al, 2016). Several mechanisms have been proposed to explain rupture reactivation including rupture in a heterogeneous distribution of prestress (Goto et al, 2012) and thermally activated slip weakening with two sequential strength drops (Galvez et al, 2016;Kanamori & Heaton, 2000).…”

Extreme scale multi-physics simulations of the tsunamigenic 2004 sumatra megathrust earthquake

“…Studies investigating the effect of more realistic geometries on shallow slip and seafloor displacement were restricted to 2D [53]. A notable exception is the 3D TohokuOki earthquake scenario presented in [34,35] that resolves seismic waves up to 0.2 Hz and includes non-planar megathrust geometry. It does not, however, include topography or fault networks.…”

Controls on Fore‐Arc Deformation and Stress Switching After the Great 2011 Tohoku‐Oki Earthquake From Discrete Numerical Simulations

“…A coseismic decrease in effective basal friction ( ) beneath the frontal wedge during the earthquake then caused the transition from a stable wedge to an extensional wedge (Conin et al, ; Cubas et al, ; Suppe, ). The reasons for the reduction in fault friction, that is, dynamic weakening, are not stipulated, but may have been due to thermal pressurization during the earthquake (Galvez et al, ; Koge et al, ; Ujiie et al, ) or some alternative mechanism.…”