View over the Maars de Moya on Petite-Terre (Moya, Mayotte, 2012). © BRGM - Dominique Tardy

Seismic activity in Mayotte: launch of an observation campaign

03.07.2019
Several hundred seismic events have been recorded on and around Mayotte since May 2018. In February 2019, several campaigns were launched on land and at sea to gain a better understanding of this ongoing seismic activity.

Since 10 May 2018, numerous earthquakes have occurred offshore from Mayotte, sometimes felt by inhabitants across the island. Accumulated observations to date suggest a phenomenon involving a combination of submarine seismic and volcanic activity. Starting on 23 February 2019, several land and sea missions, coordinated by the CNRS with support from the BRGM, the Paris Institute of Planetary Physics (IPGP), the IGN, Ifremer and the Ministry for the Ecological and Inclusive Transition, will be attempting to shed light on the mechanisms at work, in order to improve estimations of potential impacts.

In the past nine months, Mayotte has been experiencing sustained seismic activity. Despite the relatively low density of seismic coverage, given the region's moderate seismicity, the BRGM has been monitoring the phenomenon from three seismological stations on the island, with additional data from other more distant stations in the region, in the Comoros and Madagascar in particular. The analyses made by the BRGM, IPGP, the Earth Sciences School and Observatory (CNRS/University of Strasbourg) and the Karthala volcanology laboratory (CNDRS - National Centre for Scientific Documentation and Research, on Grand Comoro) have already improved the interpretation of the seismic signals.

More than 1600 earthquakes of magnitude 3.5 and more, about 50 km to the east of Mayotte, have been recorded. Of these, 29 earthquakes above magnitude 5 have been felt by the population across the archipelago and have affected buildings in some places. Furthermore, low-frequency signals of a different type, which propagate more easily over long distances, have been recorded by global networks, in particular on 11 November 2018. These signals could correspond to seismic tremors, which are imperceptible earthquakes triggered by rising magma. Since July 2018, moreover, regular signal processing by the permanent GNSS network run by the IGN shows that the six high-precision GPS stations on Mayotte have recorded a continuous eastward shift of around  14 mm/month, together with subsidence at a rate of 7 mm/month. Taken together, these observations suggest that this ongoing episode could be of the seismo-volcanic type.

Call for scientific tenders to characterise seismo-volcanic processes

In response to a BRGM initiative at the start of this seismo-volcanic episode, the scientific community has been seeking to understand the phenomena and how they are evolving. In these circumstances, the CNRS coordinated a call for tenders for co-funding by the Ministry for the Ecological and Inclusive Transition. This was sent on 29 November 2018 to over 20 French research laboratories working in the relevant field, with the aim of improving scientific observations and understanding of the phenomenon and producing better estimations of the hazards and potential impacts for this French region. This €420 000 effort will support ongoing observation missions by deploying instruments on land and at sea to produce data for immediate distribution to the scientific community. The call for tenders also covers data analysis and strengthening of the observation network.

After assessment of the proposals received by the scientific and operational committees, the steering committee selected three projects on 22 January 2019.  These projects involve 11 laboratories and 44 researchers, teaching researchers, engineers and technicians from the CNRS, IPGP, BRGM, Ifremer and the IGN.

Broad deployment of land and sea instruments from February to the summer of 2019

  1. Deployment of sea-bed seismometers: from 23 to 27 February 2019, using the SGTM's cargo ship Ylang, a team from the Paris Institute of Planetary Physics (CNRS/IPGP/Paris-Diderot University) will be deploying six sea-bed seismometers provided by CNRS-IPGP, together with  pressure sensors. The instruments are to be deployed for 6 months.
  2. Deployment of instruments in Mayotte: a team from the Earth Sciences School and Observatory (CNRS/University of Strasbourg) will travel to Mayotte in the week of 4 to 8 March 2019 to install high-precision seismology and GNSS stations in the municipal areas of Mtsamboro (northern Grande-Terre), Kani-Kéli (southern Grande-Terre) and Pamandzi (Petite-Terre). Deployment will be undertaken with support from the Mayotte and Orléans BRGM teams  and from the IGN for the retrieval and distribution of GNSS information (GNSS, the acronym for Global Navigation Satellite System, covers all satellite-based navigating systems, including the GPS and the European Galileo system).
  3. Installing a new geophysics station in the  Glorioso Islands: the OVPF-IPGP volcanology observatory on the Piton de la Fournaise has programmed a reconnaissance campaign across this uninhabited archipelago lying between the Comoros and Madagascar, and installation of a seismic station on 13 and 14 March 2019 during a rotation of troops. A second operation is planned for April 2019 to set up teletransmissions and a high-precision GNSS station.

An oceanographic campaign to undertake sea-bed observations and to detect and quantify any gas releases indicating a submarine volcano is now under discussion with Ifremer, the Ministry for the Ecological and Inclusive Transition and the Ministry of Higher Education, Research and Innovation. This could be undertaken in the spring or summer of 2019.

In addition to the deployment of instruments, a team from the University of La Réunion together with the OVPF-IPGP will undertake ground missions to consolidate knowledge on Mayotte's tectonic and volcanic history. This will include studies to clarify the island's tectonic structures, dating magmatic rocks and analysing the composition of soil gases.  All teams working in the field will be analysing and modelling the data collected.  The IGS team in charge of the permanent GNSS will be focusing on the retrieval of all GNSS data and its distribution to the entire community.

TO FIND OUT MORE

Find out more about the earthquake swarm in Mayotte

 

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