A Method to Improve the Spatial Resolution of Coseismic Gravitational Signals Retrieved from Grace Time-Variable Gravimetry

Abstract:

Limited spatial resolution is a major challenge in studying earthquake deformations with observations from GRACE (Gravity Recovery and Climate Experiment) satellite gravimetry. Significant attenuation of signal amplitudes would be introduced by truncation of GRACE spherical harmonic (SH) coefficients, and spatial filtering applied to suppress noise in GRACE monthly gravity solutions. We correct the signal attenuation and recover the “true” coseismic gravity changes based on forward modeling, an algorithm used to reduce leakage errors in previous studies. Through coseismic gravity changes predicted by a dislocation model of the 2011 Tohoku-Oki earthquake, we evaluate the reliability of the method by synthetic tests with simulated GRACE stripe errors. The results from synthetic tests indicate that the forward modeling approach is capable of recovering not only signal amplitudes but also spatial patterns of the coseismic signals. We also recover coseismic gravity changes from 2 years of GRACE monthly solutions (RL05, released by Center for Space Research) after the Tohoku-Oki earthquake, which agree well with those predicted by the dislocation model. In addition, by improving the forward modeling algorithm with the constraint of fault plane geometry, we are able to recover the original coseismic gravity changes (with full spatial resolution) from GRACE observations. Preliminary results show that the recovery of coseismic signals helps better understand the distribution of fault slips.