Excess strain in the Echigo Plain sedimentary basin, NE Japan: evidence from coseismic deformation of the 2011 Tohoku-oki earthquake

Coseismic deformation depends on both the source fault and on the elastic properties of the crust. Large coseismic deformation associated with the 2011 Mw 9.0 Tohoku-oki earthquake enabled us to investigate strain anomalies from crustal inhomogeneity. Concentrated contractional strain was observed in the Echigo Plain (Niigata-Kobe Tectonic Zone) before the Tohoku-oki earthquake, whereas continuous and campaign global navigation satellite system measurements show a widespread distribution of coseismic extensional strain in and around the plain. A 1-D displacement profile shows high strain (7.2 ± 0.7 microstrain) in a 17 km long section across the Echigo Plain and low strain (3.3 ± 0.4 microstrain) along a 15 km long section east of the plain, despite the latter being closer to the megathrust fault source. We performed numerical modelling of coseismic deformation using a heterogeneous subsurface structure and successfully reproduced excess extension in the plain, which is filled by low-rigidity sediments. This study demonstrates the importance of considering heterogeneous crust in deformation modelling.