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We evaluate response of Mid‐Niigata during the preseismic, coseismic, and postseismic periods of the 2011 Mw9.0 Tohoku‐oki earthquake by analyzing strain distributions based on a dense Global Positioning System network. Decomposition of the coseismic E‐W strain according to its wavelength shows localized elastic extension, while persistent localized contraction in the short‐wavelength component within a narrow zone of 40‐ to 60‐km width is significant before and after the event, implying the persistence of an inelastic process. Differences in the amplitude and horizontal location of the localized deformation suggest that elastic heterogeneities of the crust, acting in different sense before and after the earthquake, affect the deformation in Mid‐Niigata as well. We model localized deformation in the preseismic and postseismic period considering an aseismic fault slip and a weak elastic zone as deformation sources. Our kinematic models suggest vertical decoupling between the weak elastic layer and the basement rock, implying that the preseismic and postseismic strain rate patterns represent direct effects of the shallow portion of the crust in Mid‐Niigata. Although model parameters are not well constrained, we find that faults cutting the lower crust and a part of the upper crust, and an anomalously weak zone of a 40‐ to 60‐km width located above the fault explain the data. Our simple model shows that both inelastic and elastic sources are essential in the deformation mechanism of the Mid‐Niigata area in northern Niigata‐Kobe Tectonic Zone.

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.

We analyze Global Navigation Satellite System (GNSS), Interferometric Synthetic Aperture Radar, and accelerometer data within the San‐in Shear Zone in order to clarify the coseismic and postseismic slip distributions associated with the Mw6.2 2016 Central Tottori earthquake. Inversion of the coseismic displacement data to estimate the slip distribution on the rupture fault shows a patch of large slip to the northwest of the hypocenter of the mainshock location. Relocated aftershocks and off‐fault seismicity 1 month after the mainshock are in agreement with stress change patterns caused by the mainshock fault. Inversion of near‐field GNSS displacements in 7 months following the earthquake under the assumption of afterslip does not show a preferred slip patch but rather a smooth distribution of the slip at shallow depths. Restricted slip propagation of afterslip on the 2016 event might suggest that inland faults in the San‐in Shear Zone are immature. Limited resolution of the GNSS data might inhibit us from finding the slip at depth.

Northeast Japan is a typical island arc related to the Pacific plate subduction. The 2011 Mw 9.0 Tohoku-oki earthquake provided a unique opportunity to analyze crustal deformation with different boundary conditions, similar to a gigantic rock deformation experiment. We review findings obtained through various observations and data analyses in Northeast Japan, focusing on the crustal deformation in different timescales. The occurrence of the M9 earthquake solved the ongoing paradox that the geodetic strain rate is an order of magnitude larger than the geologic estimate, showing that the centennial geodetic observation had mainly captured the elastic strain accumulation. Along the localized contraction zone along the Japan Sea coast, a comparison of postseismic and interseismic deformation patterns revealed a significant contribution of inelastic deformation, which plays an essential role in long-term deformation. Along the Pacific coast, rapid interseismic subsidence and unexpected coseismic subsidence were followed by a rapid postseismic uplift, indicating that viscous relaxation in the mantle is of essential importance. These findings advance our understanding of plate interactions and the tectonic evolution of the island arc. ▪ The 2011 Tohoku-oki earthquake provided the most complete crustal deformation data set ever for interseismic, coseismic, and postseismic periods. ▪ The discrepancy between the geologic and geodetic deformation rates in Northeast Japan is attributed to an elastic strain due to interplate locking. ▪ A significant contribution of inelastic deformation in the island arc crust is identified through a comparison of interseismic and postseismic deformations. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.