5:15 PM - 6:30 PM
[SSS05-P04] Estimation of strain-rate field in the Japanese Islands using optimized distance-decaying constants
Estimation of strain-rate field based on Global Navigation Satellite System (GNSS) data has been performed to extract local crustal deformation (e.g., Meneses-Gutierreza and Sagiya, 2016; Nishimura et al., 2018). The method of Shen et al. (1996) has been frequently used to estimate the strain rate. In this method, a distance-decaying constant is assumed and used for Gaussian weighting of the observation point data. The accuracy of the strain rates at grid points should depend on the coarseness of the observation points. Therefore, Shen et al. (2015) proposed a method to optimize the distance-decaying constant for each grid point using the sum of the Gaussian weightings as a constraint.
In this study, we use horizontal displacement components from the F3 solution (Nakagawa et al., 2009) of GEONET, the GNSS array by the Geospatial Information Authority of Japan (GSI), with removing offsets due to major earthquakes and antenna replacement from February 1997 to February 2020. The optimal distance-decaying constant and strain-rate fields are estimated for each grid point divided by 0.3 degrees of latitude and longitude respectively, before and after the 2011 Tohoku megathrust earthquake. The constraint is set so that the estimation errors at the observation points are the smallest.
With respect to the estimation results before the 2011 Tohoku earthquake, the maximum shear strain rate and the dilatation rate are negatively correlated as a whole (correlation coefficient is about -0.5). The areas with high shear strain rate and high compressive rate (negative dilatation rate) are located around Shikoku, Shizuoka, Tokyo, and Niigata, which may indicate the plate coupling associated with the subduction of the Philippine Sea Plate and the existence of the Niigata-Kobe tectonic zone. By contrast, the above correlation collapses in the estimated results after the 2011 Tohoku earthquake. In particular, both the shear strain rate and the expansion rate (positive dilatation rate) are higher on the Japan Sea side from Akita to Aomori in the northern Tohoku region. This relationship is not observed in the southern Tohoku region. In addition, rotational components estimated simultaneously with the strain rates show opposite directions in the northern and southern parts of the Pacific coast of the Tohoku region. Our results suggest that there was a notable north-south difference in the postseismic deformation of the 2011 Tohoku earthquake.
In this study, we use horizontal displacement components from the F3 solution (Nakagawa et al., 2009) of GEONET, the GNSS array by the Geospatial Information Authority of Japan (GSI), with removing offsets due to major earthquakes and antenna replacement from February 1997 to February 2020. The optimal distance-decaying constant and strain-rate fields are estimated for each grid point divided by 0.3 degrees of latitude and longitude respectively, before and after the 2011 Tohoku megathrust earthquake. The constraint is set so that the estimation errors at the observation points are the smallest.
With respect to the estimation results before the 2011 Tohoku earthquake, the maximum shear strain rate and the dilatation rate are negatively correlated as a whole (correlation coefficient is about -0.5). The areas with high shear strain rate and high compressive rate (negative dilatation rate) are located around Shikoku, Shizuoka, Tokyo, and Niigata, which may indicate the plate coupling associated with the subduction of the Philippine Sea Plate and the existence of the Niigata-Kobe tectonic zone. By contrast, the above correlation collapses in the estimated results after the 2011 Tohoku earthquake. In particular, both the shear strain rate and the expansion rate (positive dilatation rate) are higher on the Japan Sea side from Akita to Aomori in the northern Tohoku region. This relationship is not observed in the southern Tohoku region. In addition, rotational components estimated simultaneously with the strain rates show opposite directions in the northern and southern parts of the Pacific coast of the Tohoku region. Our results suggest that there was a notable north-south difference in the postseismic deformation of the 2011 Tohoku earthquake.