Limitations of gravimetric forward modelling in gravity inversion with seismic constraint: lithospheric studies

Joint gravity–seismic inversion is a strong approach for imaging crustal and lithospheric structure, yet its success  highly depends on the formulation of the gravimetric direct problem and the quality of input datasets. Here, we investigate how commonly used global and regional grids affect forward gravimetric modelling and the subsequent interpretation of crustal structure in complex tectonic environments.

Following the methodology of Uieda et al. (2017), we construct forward gravimetric models for the Moho depth, based on multiple datasets: SGG-UGM2 gravity measurements, CRUST1.0 crustal thickness models, GlobSed sediment grids, and Gebco bathymetry. We explore the effects of grid resolution, interpolation strategies, and reference model choices on the gravity response, highlighting their influence on the information available to joint inversion schemes.

Previous applications to passive margins provide an example for assessing robustness and sensitivity of the forward-modelling strategy. Extending the approach to a tectonically and magmatically complex region – Azores triple junction – demonstrates how variations in input datasets reveal lateral and vertical heterogeneities. Forward-model experiments indicate which features of the crust are robustly resolvable and how gravity inversion with a seismic constraint can illuminate the nature of the crust, including magmatic additions and crustal thickening.

Our results emphasize that careful selection and treatment of gravity and auxiliary datasets is crucial to maximize geological information from inversions. Explicit consideration of forward-model assumptions, grid effects, and seismic constraints enhances confidence in inferred lithospheric structures, providing a practical framework for integrating multidisciplinary geophysical data in tectonically complex regions.

In addition to regional-scale studies, this methodology can be applied in platform extension projects, providing a cost- and time-efficient preliminary assessment of extensive areas. By highlighting lateral and vertical heterogeneities and identifying zones where gravity responses are most sensitive to subsurface structure, forward-model experiments can guide the prioritization of future data acquisition. Such an approach allows for targeted deployment of more detailed seismic or geophysical surveys, reducing overall exploration effort while maximizing geological insight across large and complex tectonic domains.