Investigation on the Postseismic Deformation Associated with the 2011 Tohoku Earthquake Based on Terrestrial and Seafloor Geodetic Observations: To Evaluate the Further Seismic Hazard Potential on the Plate Interface Beneath the Northeastern Japanese Islands
The 2011 Tohoku Earthquake (M9.0), which occurred on the plate boundary between the subducting Pacific plate and continental plate has been associated with postseismic deformation, including aseismic slip at the plate interface (postseismic slip). In order to evaluate the potential for further seismic activity, we investigated the spatial and temporal evolution of the postseismic slip based not only on terrestrial GPS data but also on seafloor geodetic data. We estimated the displacements due to the postseismic slip by subtracting the displacements due to large aftershocks and viscoelastic relaxation from the original displacement time series data and used a time-dependent inversion method to estimate the postseismic slip distributions. The resultant postseismic slip distributions depend strongly on the assumed value of the viscosity. However, the following two features are independent of the viscosity assumption: (1) large postseismic slip has been occurring at a very shallow ( ≤ 20 km in depth) portion of the plate interface south of the area of huge coseismic slip and (2) significant postseismic slip has occurred at a deep (approximately 50 km in depth) portion of the plate interface. The results suggest that the elastic strain and the stress concentrated at the plate interface at a depth of approximately 30 km in the segment off the Boso Peninsula have not yet been released and continue to generate large aftershocks.
KeywordsGPS Interplate coupling Postseismic slip Postseismic deformation Seafloor geodesy Viscoelastic relaxation
The authors would like to thank JCG for providing GPS/A data. GPS data were provided by JNES, GSI, and NAO. The present study was supported through the MEXT project, “Evaluation and disaster prevention research for the coming Tokai, Tonankai and Nankai earthquakes” and by JSPS KAKENHI (20244070). Figures were created using GMT software (Wessel and Smith 1998).
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