Detection of plastic strain using GNSS data of pre- and post-seismic deformation of the 2011 Tohoku-oki earthquake

Abstract

In general, there are three mechanisms causing crustal deformation: elastic, viscous, and plastic deformation. The separation of observed crustal deformation to each component has been a challenging problem. In this study, we succeed in separating plastic deformation as well as viscous deformation in the northern Niigata–Kobe Tectonic Zone (NKTZ), central Japan, using GNSS data before and after the 2011 Tohoku-oki earthquake, under the assumptions that elastic deformation is principally caused by the plate coupling along the Japan trench and that plastic deformation ceased after the Tohoku-oki earthquake due to the stress drop caused by the earthquake. The cessation of plastic deformation can be understood with the concept of stress shadow used in the field of seismic activity. The separated strain rates are about 30 nanostrain/year both for the plastic deformation in the preseismic period and for the viscous deformation in both the pre- and post-seismic periods, which means that the inelastic strain rate in the northern NKTZ is about 60 and 30 nanostrain/year in the pre- and post-seismic periods, respectively. This result requires the revision of the strain-rate paradox in Japan. The strain rate was exceptionally faster before the Tohoku-oki earthquake due to the effect of plastic strain, and the discrepancy between the geodetic and geologic strain rates is much smaller in usual time, when the plastic strain is off. In order to estimate the onset timing of plastic deformation, the information on stress history is essentially important.

The Delayed Decrease of Seismicity In The Eastern Margin of The Japan Sea Due To The Megathrust Event In 2011 Along The Japan Trench

“…The estimated loading rates of this region are a several times larger than those obtained from the GPS data in the plane strain framework. However, our finding that the pre-M9 term rate is the double of the post-M9 term well agrees with that obtained for EW-deformation rate in Niigata (Fukahata et al, 2020). For a long-term hazard estimation of the eastern margin of the Japan Sea area, the rates we obtained will be another proxy values.…”

“…The rate of horizontal strain obtained from GPS data for the eastern margin of the Japan Sea before the M9 event (Sagiya, 2004) is a quarter of what we obtained in this study. Fukahata et al (2020) obtained EW-direction deformation rates from GPS data in the Niigata region as 6×10 -8 /y for pre-M9, and 3×10 -8 /y for post-M9 terms. Their strain rates are two dimensional.…”

Consistent Estimation of Strain Rate Fields from GNSS Velocity Data Using Basis Function Expansion with ABIC

“…For example, applying the method to GNSS data in Japan, Sagiya et al (2000) found a high strain-rate region named the Niigata-Kobe tectonic zone (NKTZ) that passes through central Japan. Furthermore, through the analysis of GNSS data in this region before and after the 2011 Tohoku-oki earthquake, Meneses-Gutierrez and Sagiya (2016) succeeded in separating elastic strain and inelastic strain; Fukahata et al (2020) further succeeded in separating the inelastic strain into plastic and viscous strains. Nishimura et al (2018) clarified strain partitioning between inland active faults and the interplate coupling in southwest Japan.…”

Azimuthal differences and changes in strain rate and stress of the Japanese Islands deduced from geophysical data

“…To estimate the strain-rate eld, we use the surface displacement data of GEONET, a GNSS array by the Geospatial Information Authority of Japan (GSI), as in many previous studies (e.g., Sagiya et al 2000;Nishimura et al 2018;Fukahata et al 2020). In recent years, several methods have been developed for calculating strain rates from surface displacement data that can take into account the spatial heterogeneity of station spacing (Shen et al 2015;Sandwell and Wessel 2016;Okazaki et al 2021).…”