Principal Component Analysis of 3-Dimensional Postseismic Deformation of the 2011 Tohoku-oki Earthquake during 2012-2019

Abstract:

In northeast Japan, significant crustal deformation has been observed by the continuous GNSS network (GEONET) and its pattern has changed drastically before and after the 2011 Tohoku-oki earthquake. These spatio-temporal variations of the crustal deformation reflect various processes. Meneses-Gutierrez and Sagiya (2016) demonstrated that crustal deformation in the northern Niigata-Kobe tectonic zone contains significant contribution of inelastic deformation. In this study, in order to separate deformation components in the northeast Japan, we analyze spatio-temporal change of horizontal as well as vertical velocities at the GNSS stations located in the Tohoku region. First, we compare the temporal changes of the horizontal and vertical components before and after the Tohoku-oki earthquake. Focusing on the post-seismic period, while the horizontal velocities rapidly decrease over time, the vertical velocity pattern looks pretty persistent. These different behaviors imply multiple physical processes contribute to the postseismic deformation, just as pointed by Meneses-Gutierrez and Sagiya (2016). In order to separate such deformations that have different spatio-temporal changes, we apply the principal component analysis (PCA) to the GNSS data. We applied PCA to F3 solution of GEONET for eight years after the Tohoku-oki earthquake. Horizontal as well as velocities are estimated from 2-years long time series at 108 sites in northeast Japan with 1-month offsets. In total, the number of the analyzed velocity data is 108 (sites) x 96 (months) = 324. As a result, we identified 5 spatio-temporal modes of deformation. The first and second modes include post-seismic deformation, the first mode include linear and logarithmic function with long time constant and the second mode include logarithmic function with short time constant (1~2 years). The third mode represents seasonal changes. The fourth and fifth modes include earthquake displacement occurred at the observation time (2015 Miyagi-oki, 2019 Yamagata-oki). This result shows that it is not possible to quantitatively separate elastic and inelastic components at present, but this method has a certain effect on the separation of deformation components that have different spatio-temporal change rates.