Problems of the Joint Inversion of Temporal Gravity Variations with the Data on Land and Seafloor Displacements: a Case Study of the Tohoku-Oki Earthquake of March 11, 2011

Abstract

The methodology for joint inversion of various types of data on the Tohoku-Oki earthquake is presented. It is shown that data of satellite geodesy (GPS), SAR interferometry, and co-seismic GRACE gravity anomalies are overall fairly well consistent with each other. However, the resolution of these data is not high and the rupture surface model based on them is smoothed. Meanwhile, the measured and calculated data agree very well which creates the illusion that the resulting solution is close to the real process. The solution of the inverse problem based on displacements of the ocean bottom stations shows that the rupture surface models based on the measurement data on land and/or GRACE gravity anomalies alone may significantly differ from the real co-seismic displacement field. If the rupture surface is specified inaccurately, then the high quality of data fitting and the chessboard test do not guarantee high accuracy of the solution. A similar situation is also observed in estimating the degree of locking along the plate contact within locked segments of a subduction zone. In the paper it is emphasized that the accuracy of inverse problem solution mostly depends on how the geodynamic model matches the real process. For increasing the accuracy and degree of detail of the solution, the efforts need to be focused on a more adequate description of the physics of the co-seismic and post-seismic process in parallel with a more detailed description of the geological structure of a rupture area with allowance for the discontinuities of the medium and a more detailed assignment of the distribution of physical parameters.