Limitations of dislocation models for quantifying surface displacement induced by the buoyancy of ascending dikes

Dislocation models, whether analytical or numerical, are widely used to interpret surface displacements induced by magmatic intrusions. Deep learning methods developed for interpreting InSAR data are also trained using synthetic data produced by dislocation models. While these models are well suited to describing the deformation and stresses induced by the emplacement of magma within a planar structure, they neglect buoyancy, which is the main driving mechanism for magma ascent within the crust. We use analog experiments to highlight the effect of buoyancy on dike-induced surface deformation. Finite volumes of air or silicone oil are injected into gelatin, which is characterized by elastic behavior. The fluid-filled crack rises vertically through the gelatin due to buoyancy. Its position, shape, and orientation are tracked by side cameras, and the surface displacement of the gelatin is measured simultaneously by photogrammetry and pixel shift tracking from images acquired by four synchronized cameras located at the top of the experimental setup. We compare the displacement field estimated from the dislocation model with the recorded displacement field in the laboratory. We show that while dislocation models with realistic opening distributions are able to reproduce the displacement field profile fairly accurately, they systematically underestimate vertical displacement in the near field and overestimate horizontal displacements for a buoyant ascending crack. Our study shows that buoyancy of dikes triggers upward displacement of the Earth’s surface, which is not accounted by dislocation models. We discuss in more detail the potential consequences of this bias in dislocation models for the interpretation of geodetic data in volcanic areas.