Vertical displacement off Mayotte

Vertical displacements off Mayotte: In the rapid response phase to the volcanic crisis, INSU DT SBE37 pressure sensors have been deployed since February 2019 and the first INSU OBS deployments in Mayotte, with the objective of acquiring data that would allow the quantification of possible sudden multi-centimetric or decimetric displacements, should they occur (Feuillet et al., 2021, Peltier et al., 2022)

Currently, given the absence of probable earthquakes and movements at shallow depths, the scientific questions require the quantification of slow movements (deep subsidence, transients). The inherent drift of pressure sensors (whether SBE37s or Paroscientific-type geodetic sensors) limits our ability to determine slow movements since the geophysical trend may be of the same order of magnitude or less than that of the sensor drift. A new type of instrument, called an AOA, which alternately measures the ambient pressure (seabed) and a zero (atmospheric pressure), allows us to estimate the sensor drift in situ. This type of sensor has been deployed in Mayotte since the MAYOBS15 campaign (April 2020, Peltier et al., 2022).

The second factor limiting our ability to assess vertical motion from pressure is ocean dynamics which generates a signal of the order of a few centimetres with periods ranging from hours to weeks (or months). One option to significantly reduce the impact of ocean dynamics is to look at the differential signal between different sites, since the common ocean signal is then removed in the difference.

Since July 2022 (MAYOBS23), two AOAs have been installed, one in the centre of the Crown and the other at a reference site to the north and outside the area of active microseismicity.