Observability of Seafloor Deformation in OBP Records: an A-0-A Experiment in the Context of the Mayotte Volcanic Crisis, Using Ocean Models

Ocean bottom pressure (OBP) records are an important source of information for monitoring seafloor motion due to tectonic and magmatic processes, such as earthquakes and volcanic eruptions, at a centimeter-level precision. Although centimeter-level resolution is commonly accessible with high-resolution sensors;  monitoring seafloor deformation of a few centimeters through time with OBPs is challenging due to the instrumental drift and the existence of oceanic variations at different timescales.

In the context of the Mayotte volcanic crisis, which occurred in the western Indian Ocean in 2018 and was characterized by a series of more than 10,000 small-magnitude earthquakes and a subsidence of tens of centimeters (Peltier et al., 2022), three RBR Ambient-Zero-Ambient (A0A) drift-controlled pressure gauges were consecutively deployed in 2020, 2021 and 2022 for seafloor vertical deformation monitoring. The A0A system allows the in-situ estimation of the instrumental drift  by periodic venting from ocean pressures to a reference atmospheric pressure (Wilcock et al., 2021). Since no significant vertical ground displacements are recorded by ground GNSS stations since 2020, the overall objective of this study is to assess the calibration method of these innovative pressure gauges, reduce the oceanic “noise” in corrected OBP records and thus discuss our ability to observe any seafloor deformation in the Mayotte region.

To do so, we investigated the use of numerical models, including available global ocean circulation reanalyses (OGCMs) and barotropic simulations, in order to better understand the relative influence of each processes evolving at different timescales, to reduce the oceanic “noise” in drift-corrected OBP records and thus improve our ability to derive accurate estimates of seafloor motion in the Mayotte region. In addition, we exploited temperature and salinity collected by repetitive glider transects to validate OGCMs in the region and quantify the contribution of unresolved fine-scale processes, such as sub-mesoscale eddies, to OBP records. 

Our results provide valuable insights into the feasibility of using numerical modeling for improving the accuracy of OBP-based monitoring in the context of the Mayotte seismic crisis as well as for other seafloor deformation monitoring. It also has important implications for future A0A deployments and in the perspective of the planned MARMOR seafloor cabled observatory.

References 

Peltier, Aline, et al. "Ground deformation monitoring of the eruption offshore Mayotte." Comptes Rendus. Géoscience 354.S2 (2022): 1-23.

Wilcock, W. S., Manalang, D. A., Fredrickson, E. K., Harrington, M. J., Cram, G., Tilley, J., ... & Paros, J. M. (2021). A thirty-month seafloor test of the A-0-A method for calibrating pressure gauges. Frontiers in Earth Science, 8, 600671.