Stress change before and after the 2011 M9 Tohoku-oki earthquake

Abstract

Megathrust systems hold important clues for our understanding of longand short-term plate boundary dynamics, and the 2011 M9 Tohoku-oki earthquake provides a data-rich case in point. Here, we show that the F-net moment tensor catalog indicates systematic changes in crustal stress in the years leading up to the M9, due to the co-seismic effect, and for the last few years due to viscous relaxation. We explore the match between imaged stress change and the perturbations that are expected from 3-D, mechanical models of the visco-elastic relaxation and afterslip effects of the M9. While these models were constructed based on geodetic and structural seismology constraints alone, they match many characteristics of the seismicityinferred stress change. This provides additional confidence in the modeling approach, and new clues for our understanding of plate boundary dynamics for the Japan trench. The success of deterministic approaches for explor-*

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

“…In particular, LFEs at Zao are distributed around the edge of a low‐velocity zone with a high Poisson's ratio, suggesting the presence of fluid (Niu et al, ). Therefore, the observed temporal change in focal mechanisms and activation of LFEs at Zao (Figure f) could also be resulted from stress changes due to the Tohoku earthquake (Becker et al, ). Such an interpretation of stress triggering under the potential existence of fluids is often preferred in volcanic or geothermal regions (e.g., Brodsky & Prejean, ; Hill et al, ; Kato et al, ).…”

“…Considering the transition from DC-A to CLVD-D in 2013 associated with the increase in seismicity (Figure 3f), our interpretation is that group DC-A was deactivated and CLVD-D was activated in 2013. The reduction of the compressional stress in E-W direction after the Tohoku earthquake (Becker et al, 2018) may have inhibited a pure double couple (DC-A) but have facilitated CLVD-D mechanisms.…”

Evidence of Changes of Seismic Properties in the Entire Crust Beneath Japan After the Mw 9.0, 2011 Tohoku‐oki Earthquake

“…Figure 6 shows the map of the modeled seismic velocity changes for the period band of 8 to 30 s, and the map of the coseismic dilatation at 20 km in depth. The coseismic dilatation is calculated using a three-dimensional (3-D) depth-dependent viscoelastic finite element model based on the GPS displacements (Becker et al, 2018;Freed et al, 2017). Both of these maps are smoothed over 100 km before mapping.…”

Intermittent fracturing in the middle continental crust as evidence for transient switching of principal stress axes associated with the subduction zone earthquake cycle

“…Reversal in the stress axes on a much shorter time scale is inferred in studies of elastic rebound after major earthquakes (Hyndman and Wang, 1993;Ozawa et al, 2011Ozawa et al, , 2012Hasegawa et al, 2012;Wang et al, 2012;Avouac, 2015;Klein et al, 2016;Becker et al, 2018;Govers et al, 2018). Viscoelastic relaxation of the reversal from extension back to compression is modeled to take years to decades (Klein et al, 2016;Becker et al, 2018). For subduction megathrust earthquakes, reversal is limited to the overriding upper plate (Hyndman and Wang, 1993;Wang et al, 2012).…”

“…Such a switch could be due to the interplay between tectonic and gravitational forces (Molnar and Lyon-Caen, 1988). However, on a shorter time scale, reversal of stress axes is typical of co-to early postseismic rebound after earthquakes (e.g., Hasegawa et al, 2012;Wang et al, 2012;Becker et al, 2018;Govers et al, 2018). In this study, field structures in the Neves area (eastern Alps, Italy) are used to assess the mechanism of transient fracturing at midcrustal levels in the hanging wall of a continental subduction megathrust.…”