A decadal‐scale deformation transient prior to the 2011 M_w 9.0 Tohoku‐oki earthquake

Abstract

GPS time series in northeast Japan exhibit nonlinear trends from 1996 to 2011 before the Mw 9.0, 2011 Tohoku‐oki earthquake. After removing reference frame noise, we model time series as linear trends plus constant acceleration, correcting for coseismic and postseismic effects from the numerous Mw ∼ 6.5+ earthquakes during this period. We find spatially coherent and statistically significant accelerations throughout northern Honshu. Large areas of Japan outside the Tohoku region show insignificant accelerations, demonstrating that the observation is not due to network‐wide artifacts. While the accelerations in northern Tohoku (Sanriku area) can be explained by decaying postseismic deformation from pre‐1996 earthquakes, the accelerations in south‐central Tohoku appear unrelated to postseismic effects. The latter accelerations are associated with a decrease in average trench‐normal strain rate and can be explained by increasing slip rate on the Japan trench plate interface and/or updip migration of deep aseismic slip in the decades before the 2011 Tohoku‐oki earthquake.

A very long-term transient event preceding the 2011 Tohoku earthquake

“…Meanwhile, westward deviations are obvious in the data obtained for northern Tohoku, although there was no significant deviation in the Kanto district. Small southward deviations were found extending along the western coast of northern Tohoku, as has been found previously in deformation accelerations 18 . This implies that the sources of the large eastward and westward deviations were located far from the western coast.…”

“…Figure 2 shows the distribution of measured total deviations (pink arrows). As found in deformation accelerations 18 and deformations including postseismic signals 9,19,20 , large eastward deviations were observed along the eastern coast of central and southern Tohoku with a broad extension to the west. Meanwhile, westward deviations are obvious in the data obtained for northern Tohoku, although there was no significant deviation in the Kanto district.…”

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

“…A similar change of stress before the M9 is seen to the SW of this particular bin (Figure 4). Such a pre-M9 stress field modification might relate to the change in geodetically inferred deformation state of the overriding plate close to the M9 as analyzed by Ozawa et al (2012) and Mavrommatis et al (2014), and recently explored in terms of temporal evolution of coupling by Iinuma (2018). Another contribution to the stress field change as seen in Figure 6 Figure 5b), large jump due to the co-seismic effect of the M9 (cf.…”

A megathrust earthquake cycle model for Northeast Japan: bridging the mismatch between geological uplift and geodetic subsidence

“…The second term represents the effect of increasing slip deficit (interseismic locking). Locking rate could change in several years (e.g., Nishimura et al 2004;Mavrommatis et al 2014Mavrommatis et al , 2015, but this change can be regarded as short-time perturbation from the general trend of slip…”