Citizen Science for Disaster Risk Governance: Towards a Participative Seismological Monitoring of the Mayotte Volcanic Crisis

The United Nations (UN) Sendai Framework for Disaster Risk Reduction 2015–2030 aims to mitigate natural disasters, specifically in developing regions. It promotes the adoption of people-centered disaster risk reduction approaches. Hence, citizen science represents an interesting tool to engage populations in the mitigation of disaster risk, through data collection and analysis, and in the dissemination of scientific and safety information. Herein, we evaluate the potential and feasibility of a citizen science project on the island of Mayotte (in the Mozambique Channel). Mayotte has been experiencing an unexpected volcano-seismic crisis since 2018, which has generated strong anxiety in the population. To address this, we have developed a citizen seismology program to engage Mayotte’s inhabitants in seismic data processing. First, we conducted an initial test of our protocol to identify seismic events with a set of university students. We then conducted 15 interviews with members of local administrations and associations to assess the potential for engaging the general population in this project. The results show that we are able to collect reliable data from citizens with non-professional backgrounds using the protocol designed in the project. We also show a strong demand for scientific information from Mayotte’s inhabitants, associated with a robust trust in science and scientists, despite the circulation of alternative explanations for the seismicity among the population. Based on these results, our citizen science project could be positively received by Mayotte’s inhabitants, if advertised adequately. Finally, we discuss the value of these results for disaster risk reduction in vulnerable territories

Automatic detection for a comprehensive view of Mayotte seismicity

International audienc

Initial results from a hydroacoustic network to monitor submarine lava flows near Mayotte Island

In 2019, a new underwater volcano was discovered at 3500 m below sea level (b.s.l.), 50 km east of Mayotte Island in the northern part of the Mozambique Channel. In January 2021, the submarine eruption was still going on and the volcanic activity, along with the intense seismicity that accompanies this crisis, was monitored by the recently created REVOSIMA (MAyotte VOlcano and Seismic Monitoring) network. In this framework, four hydrophones were moored in the SOFAR channel in October 2020. Surrounding the volcano, they monitor sounds generated by the volcanic activity and the lava flows. The first year of hydroacoustic data evidenced many earthquakes, underwater landslides, large marine mammal calls, along with anthropogenic noise. Of particular interest are impulsive signals that we relate to steam bursts during lava flow emplacement. A preliminary analysis of these impulsive signals (ten days in a year, and only one day in full detail) reveals that lava emplacement was active when our monitoring started, but faded out during the first year of the experiment. A systematic and robust detection of these specific signals would hence contribute to monitor active submarine eruptions in the absence of seafloor deep-tow imaging or swath-bathymetry surveys of the active area

Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures

Human activity causes vibrations that propagate into the ground as high-frequency seismic waves. Measures to mitigate the COVID-19 pandemic caused widespread changes in human activity, leading to a months-long reduction in seismic noise of up to 50%. The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record. While the reduction is strongest at surface seismometers in populated areas, this seismic quiescence extends for many kilometers radially and hundreds of meters in depth. This provides an opportunity to detect subtle signals from subsurface seismic sources that would have been concealed in noisier times and to benchmark sources of anthropogenic noise. A strong correlation between seismic noise and independent measurements of human mobility suggests that seismology provides an absolute, real-time estimate of population dynamics

Analyse de la sismicité du système volcanique de Mayotte

International audienceDepuis mai 2018, une intense sismicité accompagne l'activité volcanique qui a donné naissance au nouveau volcan sous-marin de Mayotte, le mont Fani Maoré. Cette sismicité est utilisée, depuis, comme indicateur de l'évolution du système volcanique et tectonique de la zone. Le travail s'est déroulé dans le cadre du REVOSIMA (Réseau de surveillance volcanologique et sismologique de Mayotte) et s'est concentré sur la re-détection et la localisation de la sismicité enregistrée par le réseau de capteurs installé à Mayotte. Depuis son renforcement en mars 2019, ce réseau permet une bonne localisation de la sismicité

Multi-phase seismic source imprint of tropical cyclones

International audienceThe coupling between the ocean activity driven by winds and the solid Earth generates seismic signals recorded by seismometers worldwide. The 2-10 s period band, known as secondary microseism, represents the largest background seismic wavefield. While moving over the ocean, tropical cyclones generate particularly strong and localized sources of secondary microseisms that are detected remotely by seismic arrays. We assess and compare the seismic sources of P, SV, and SH waves associated with typhoon Ioke (2006) during its extra-tropical transition. To understand their generation mechanisms, we compare the observed multi-phase sources with theoretical sources computed with a numerical ocean wave model, and we assess the influence of the ocean resonance (or ocean site effect) and coastal reflection of ocean waves. We show how the location and lateral extent of the associated seismic source is period-and phase-dependent. This information is crucial for the use of body waves for ambient noise imaging and gives insights about the sea state, complementary to satellite data

Capturing Mayotte's deep magmatic plumbing system and its spatiotemporal evolution with volcano-tectonic seismicity

Since 2018, an unexpected number of earthquakes have been occurring offshore Mayotte, in the Mozambique Channel. They are linked to the eruption of the Fani Maoré submarine volcano. Using a recently developed comprehensive automatic catalog, we explore two years of the volcano-tectonic (VT) seismicity between March 2019 and March 2021, and analyse in detail the active structures of the magmatic plumbing system using ~33,000 events. The VT earthquakes highlight three magma storage zones and two aseismic conduits that have never been observed before. The temporal evolution of the seismicity reveals a probable regime change in March 2020. While before, the plumbing system reacted to the drainage of magma from a deep reservoir and to the migration of magma towards the seafloor, it is now responding to new migrations of fluids and to the redistribution of the stress-load across the system's pre-existing faults. This analysis is key to better understanding long-term volcanism worldwide

Le syndrome néphrotique chez l'adulte

ANGERS-BU Médecine-Pharmacie (490072105) / SudocSudocFranceF

Evolution of the Volcano-Tectonic seismicity associated with Mayotte's active magmatic system

International audienceIn May 2018, a seismic crisis started East of Mayotte which was widely felt on the island and has been linked to the discovery of a new active submarine edifice. In order to reconstruct the evolution of the crisis with more details on the active structures we re-analyze the seismicity from March 2019 to February 2021 and focus on its evolution throughout the eruption. We use a catalog built by using the neural network-based method PhaseNet, which considerably increased the number of detected earthquakes and enabled a deeper analysis of the seismicity variations. Moreover, the development of a new velocity model for the region allowed a precise location of these earthquakes using only land-stations data. We show that the geometry of the seismicity has evolved in the two main clusters of activity with a general decrease in activity in the proximal cluster and no decrease in activity in the distal cluster. Spatial evolutions of different sub-clusters can be identified over time. This analysis is essential to understand the dynamics of the volcanic and magmatic processes beneath Mayotte island and will provide crucial details on the dynamics of submarine eruptions