Challenges and rewards: a chronicle of vertical displacements during a seafloor spreading event at the Southeast Indian Ridge, from a seafloor pressure A0A recorder

Vertical ground deformation is a key parameter to document magmatic or tectonic processes occurring below the surface, such as magma movement, tectonic strain build-up or seismic rupture. When occurring underwater, vertical deformation can be quantified using ocean bottom pressure gauges. Although these gauges have an intrinsic resolution sufficient to document sub centimeter movements, the identification and precise quantification of vertical displacements face several challenges due to instrumental drift modeling, ocean dynamics or instrumental artefacts or orientation related sensitivity.

In 2024 and 2025, in the framework of the GEODAMS project (see related presentations Royer et al. and Olive et al., in session EGU26-GD5.1), we carried out repeated bathymetric surveys and deployed an A0A gauge - a bottom pressure recorder with a built-in drift controlling system - along with networks of seafloor acoustic transponders and moored hydrophones (Raumer et al., EGU26-SM3.2). This experiment allowed us to detect and characterize a major magmato-tectonic event which, luckily, occurred 2 months after the initial bathymetric survey and instrument installation. The detailed description of this unique event will be given in the presentation by Royer et al. (EGU26-GD5.1).

Our presentation will focus on the interpretation of the recorded pressure variations to derive a chronicle of vertical deformation, before, during and after the magmato-tectonic event. Although the instrument recorded a spectacular total subsidence close to 4 meters, the precise quantification of the deformation through the submarine eruption requires a precise modeling of the instrumental drift and changes in calibration parameters, which may be affected by likely changes in gauge orientation induced by the seafloor deformation.