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MAYOBS sea campaign following the seismo-volcanic crisis in Mayotte

Deployment of OBS and acquisition of marine geophysical data to observe and monitor the seismo-volcanic crisis in Mayotte.

MAYOBS sea campaign following the seismo-volcanic crisis in Mayotte

Publication date: 15/05/2019

Observatories, Press, Research

Related teams :
Volcanic Systems

As part of the INSU TELLUS SISMAYOTTE programme, funded by the Ministry of Research, the Ministry of Ecological Transition and Solidarity and the institutes involved (IPGP, IPGS, BRGM, IFREMER), a team of scientists from IPGP, CNRS, BRGM and IFREMER are currently on board the oceanographic vessel Marion Dufresne for the MAYOBS campaign, scheduled for May 6th to 18th  2019.

The island of Mayotte has been facing an unprecedented seismic-volcanic crisis for the past year. The activity is reflected in the presence of a highly active seismic swarm that began on May 10th 2018, 50 km east of the coast of Mayotte. Several thousand earthquakes have been recorded since then and several hundred have been felt by the population. The largest earthquake, with a magnitude of 5.8, occurred on May 15th 2018 and caused great concern among the population of the island. Since July 2018, the island has moved eastwards and sunk by more than 10 cm, which is considerable in such a short space of time. Preliminary deformation models suggest that the source of this phenomenon is the deflation of a very voluminous magma pocket located between 20 and 30 km deep, 50 km off the island (Lemoine et al., 2019).

MAYOBS campaign position map. Planned profiles and layout of the wide-area OBS network to be deployed in early 2019 (yellow circle + stars) and retrieved from the Marion Dufresne/ The precise redeployment zone is to be defined (green circle) during the campaign. Bathymetry Bathymay and SHOM campaign. Red circles: earthquakes located by the local network (BRGM catalog). Orange circles: USGS catalog locations.
The oceanographic vessel Marion Dufresne docked on Reunion Island.

The MAYOBS campaign aims to better constrain the origin of this seismic-volcanic crisis and the mechanisms involved. It is part of the SISMAYOTTE project, which has already increased the amount of instrumentation on land and at sea. On land, three new seismological stations as well as GPS and INSU mobile networks were installed last March by BRGM and IPGS. A fourth station (seismometer + GPS) was installed on Grande Glorieuse, an island neighbouring Mayotte, by the IPGP/OVSG. At sea, six INSU seismometers were deployed by the IPGP in the crisis zone in February, using the vessel Ylang.

Mission objectives

  • To recover the 6 OBS from the INSU fleet deployed in February so that the data acquired can be analysed onboard to pinpoint the location of the earthquakes also recorded by the stations on land. This will make it possible to better constrain the location of the swarm and then redeploy the OBSs over a smaller area, better suited to understanding the processes involved. Eight IFREMER micro-OBSs will also be deployed on this occasion.
Training in earthquake location software on the scientific PC.
  • Acquiring high-resolution marine geophysical data (bathymetry and bottom reflectivity using multibeam echosounders, sediment echosounder data) in the swarm area, where existing data was very patchy. Acquiring new data is essential for understanding the context of the crisis and imaging the structures, whether pre-existing or not, in the vicinity of the seismic events. Gravimetry and magnetism data will also be collected to investigate the possible presence of volcanic structures buried beneath the sediments.
  • Imaging the water column using the multibeam echosounder to detect any outflow of fluids or gases. If they are found, these fluids and gases can be sampled and analysed using a bathysonde.
  • Carrying out rock dredging on recent or ancient volcanic outpourings in order to better constrain the composition of the lavas associated with volcanism in Mauritius.
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