RGM04 to RGM23: A Coordinate Transformation for Mayotte Based on a Geophysical Model of the 2018–2022 Volcano-Tectonic Crisis

A volcano-tectonic crisis offshore the island of Mayotte, which unfolded between 2018 and 2022, generated significant deformation of the island, with absolute displacements of more than ~20 cm and relative displacements of up to ~10 cm. Because of this relative deformation, the reference network coordinates which defined the previous local reference frame, RGM04, was redetermined by GNSS in autumn 2023 to realize a new local reference frame, RGM23. A grid transformation has been computed that allows the transformation of RGM04 coordinates to RGM23 coordinates. A specific feature of this transformation is that it includes the cumulated deformation predicted by a geophysical model in addition to a standard 7-parameter transformation. The inclusion of the deformation model improves the standard deviation of the transformation post-fit residuals by 7 mm and provides a more realistic prediction of the coordinate differences between the two frames.