Earth Planets Space, Vol. 63 (No. 7), pp. 741-744, 2011
Institute of Seismology and Volcanology, Hokkaido University, Sapporo 060-0810, Japan
(Received April 7, 2011; Revised June 14, 2011; Accepted June 25, 2011; Online published September 27, 2011)
The 2011 M 9.0 Tohoku earthquake induced regional crustal deformation not only in the Japanese Islands but also in north-eastern Asia. Strain release due to mainshock faulting should cause strain redistribution in the overriding plates. The dense GPS network in Japan enables us to calculate co-seismic strain and stress changes from observed data. Strain is a more objective indicator than displacement because no reference frame is required. The co-seismic strain field clearly indicates island-scale strain redistribution. Huge extensional strain changes were concentrated in the southern Iwate and northern Miyagi regions, with a maximum value of 45 × 10-6, which might correspond to approximately 225 to 450 years of strain accumulation. This implies relatively large strain accumulation and release in these regions. Small strain decay was observed in the northernmost Niigata-Kobe tectonic zone and a possible anomalous Coulomb failure stress change was observed in the Mt. Fuji region. Earthquakes triggered in the above regions might be associated with these anomalies, and/or these non-uniform crustal deformations may reflect crustal heterogeneity.
Key words: The 2011 off the Pacific coast of Tohoku Earthquake, GPS, principal strain, maximum shear strain, triggering earthquake, Coulomb failure stress change, subsurface structure.