GPS measured static and kinematic offsets at near and far field of the 2011 Mw 9.0 Tohoku-Oki earthquake

Abstract

The Mw 9.0 Tohoku-Oki earthquake that hit the mainland Japan on 11th March, 2011 had resulted a devastating Tsunami due to an active thrusting between the Pacific and the North American Plates. Static and kinematic offsets at the offshore epicentre of the Mw 9.0 event remain unanswered and being investigated along with their near and far field limiting distances from the epicentre. Accordingly, offset measurements from 60 continuously operating IGS and GEONET GNSS stations were radially classified from the epicentre and interpreted with analytical models to find their linear offset decay rates. Co- and post-seismic static positional anomaly offsets of sixty days show almost all near field stations had strong or appreciable eastward or south eastward static shifts. Near stations (1.5 m. Spatial models of projected N-S static and kinematic offsets show their asymmetrical distributions around the epicentre with maximum model offset of −1.84 m displaced towards south at ∼45 km north of the epicentre. The Tohoku-Oki earthquake produced a resultant kinematic offset of ∼10.2 m towards East at its offshore epicentre; while the estimated near field static offset is ∼9.82 m. However, both estimates are bigger than double the resultant offset measured value (∼4.3 m) in the Japanese mainland using GPS. The difference in the kinematic and static near field offsets highlight that the near surface had elastic or in-elastic kinematic strain dissipation as against the lithospheric level viscoelastic static response, which resulted rapid kinematic strain release (1.12 cm/km) within the limiting radius of ∼220 km from the Tohoku-Oki epicentre. Keywords: 2011 Tohoku earthquake, GPS time series, Near and far field, Static and kinematic offsets, Spatio-temporal model