Numerical Modelling of Fault-Slip-Induced Satellite Gravity Signals in a 3D Viscoelastic Earth: Application to the Japanese Subduction System

The spatio-temporal variations of the Earth’s gravity field recorded by satellites have been shown to provide unique insight into mass redistributions during and after major subduction-zone earthquakes, and to reveal anomalous signals preceeding two great ruptures, attributed to rapid aseismic deformations of subducted plates. Understanding these gravity signatures is important for studying subduction system dynamics throughout the earthquake cycle and for improving regional seismic risk assessment. Physics-based numerical simulations are therefore needed in order to model pre- to post-seismic satellite gravity signals, taking into account the 3D structure of the subducting zone, including lateral heterogeneities in the mantle rheology and lateral variations in crustal thickness. In this study, we apply a novel numerical approach to simulate gravity perturbations induced by fault dislocations in a 3D viscoelastic Earth using a Spectral-Infinite-Element (SIE) method, implemented in the SPECFEM-X numerical code. Considering examples of dislocation within a subducted slab, we examine the sensitivity of the surface gravity signals to 3D slab geometry and material structure, including the effects of low-viscosity layers, mantle wedge and cold nose. This approach enables us to investigate the sources of the pre-seismic gravity anomalies prior to the 2011 Mw 9.1 Tohoku earthquake through realistic 3D Earth models and state-of-the-art simulation setups. The findings of this study underscore the importance of numerical simulations in gravitational geodesy as well as in seismic hazard assessment.