3D numerical modelling of gravity perturbations due to short-term slab deformations at the Japan subduction zone

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ID: 321936
2026
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Abstract
Summary Anomalous medium-scale gravity gradient changes reported prior to the 2011 $\rm M_w$ 9.0 Tohoku and the 2010 $\rm M_w$ 8.8 Maule earthquakes have been attributed to transient extensional deformations of the subducting slabs at depths of ~150–300 km. With a regional-scale extent and weak associated surface displacements, these signals and their deformation sources are not well understood. Our aim here is to improve their modelling by taking into account the 3D elastic structure of the subduction zone, and by assessing how the surface observables respond to variations in the spatial distribution and the depth of the deformation source. Taking the case of the pre-Tohoku signals, and representing slab extension with ensembles of dislocations, we investigate the corresponding gravitational and surface displacement signals using fully three-dimensional spectral-infinite-element simulations implemented in the numerical code SPECFEM-X, incorporating a realistic subduction-zone geometry. For the considered deep deformations, our results show a limited impact of the lateral elastic structure on the surface displacement and geoid signals, which differ by less than ~2% and ~3% respectively from the purely radially layered case. The degree of the spatial distribution of the deformation and the depth more strongly impact the relative amplitudes and the smoothness of the gravity and surface displacement signals. Broadly distributed slab deformation leads to a reduction in the extremum amplitude of the vertical surface displacements by up to ~40% compared to the results obtained for highly localized slab deformation of similar magnitude, whereas the amplitude of the medium-scale gravity gradient signals decreases by ≤20% only. These surface displacement and gravity gradient signals are attenuated by ~90% and ~60%, respectively, when moving the source depth from 100 to 500 km. In all cases, broader-scale gravity gradient signals are obtained. Thus, while distributed deformations contribute to smoothing the gravity signals and reducing the amplitude of the corresponding surface displacements, they still do not account for the required sub-centimetric level of ground motions. Our results finally provide a quantitative framework for interpreting intermediate-scale GRACE pre-seismic anomalies at subduction zones.
Reference Key
openalex_W7169872018 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Rajesh Parla, Isabelle Panet, Hom Nath Gharti, R Martin, Dominique Rémy, Bastien Plazolles
Journal geophysical journal international
Year 2026
DOI
10.1093/gji/ggag293
URL
https://doi.org/10.1093/gji/ggag293
Keywords Keywords not found

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