Seismic damage scenarios for Mayotte: a tool for disaster management

Abstract

A new marine volcano is erupting offshore Mayotte since May 2018, generating numerous earthquakes. The population felt many of them and the stronger shaking of the ongoing sequence caused slight damage to buildings. Historical records also confirm that damaging earthquakes had occurred in the past in this region. Seismic damage scenarios are a key tool for supporting the decision-making process, the preparedness, and for designing appropriate emergency responses. This paper provides the outcomes of a work consisting in improving the seismic risk assessment as a part of disaster risk governance and exposes the scientific background of this workflow. It illustrates its use with two earthquakes. Related post-seismic surveys provide observations that are useful to check the validity of the reference dataset. The paper also discusses the main characteristics of the rapid loss assessment tool that has been developed to provide operational information for crisis management.

Site effects observations and mapping on the weathered volcanic formations of Mayotte Island

“…Since the beginning of the 2000s, numerous local seismic hazard studies have shown that the Mayotte territory presents superficial geological formations likely to undergo lithological site effects [e.g., Audru et al, 2002Audru et al, , 2010. This led us to produce, in the first months of the crisis, a new lithological site effects map at regional scale dedicated to the calculation of strong motion maps and damage scenarios for crisis management purposes [Taillefer et al, 2019[Taillefer et al, , 2022.…”

“…This map has been upgraded since then including the analysis done in the framework of the revision of the local seismic hazard mapping of Mayotte, a study in progress on behalf of the local authorities. This paper describes the upgraded version of the preliminary map described in Taillefer et al [2019Taillefer et al [ , 2022. For practical reasons of constrained time delays and costs, we decided to use only the available data (i.e., without carrying out additional measurement) and to base our site effects classification on the soil classes A-E derived from the European building code EuroCode 8 (EC8) [NF EN 1998-5, 2005] and described in Table 3.…”

Relative Sea Level and Coastal Vertical Movements in Relation to Volcano-Tectonic Processes at Mayotte Island, Indian Ocean

“…Recent volcano-seismic events in unexpected places or with significant unforeseen impacts challenge our understanding of volcanic activity. First, these events suggest that the role of volcanic activity on local natural hazards should be reconsidered [1][2][3][4][5], promoting specific studies on the reduction in risk [6] associated with volcanic activity [7][8][9][10][11][12]. Second, the potential interrelationship between short-term volcanic activity and long-term volcanotectonic evolution challenges our understanding of volcanic processes and the evolution of Earth's surface.…”

“…Mayotte Island (Comoros archipelago, SW Indian Ocean, between Africa and Madagascar) has experienced significant seismic activity since May 2018, with more than 11,000 reported earthquakes of up to magnitude 5.9, including unusually long-period events (more than 400) and surface deflation of up to 200 mm/yr [19,32]. This seismic activity [19,[32][33][34] GeoHazards 2024, 5 and petrological and geophysical analyses [35,36] underline the presence of magma reservoirs at 20-30 km depth, 50 km [37] and 70 km from Petite Terre Island, Mayotte. Details of the geometry of the active system have been improved by tomography of the area [38] and petrological analysis suggests that the primitive magma came from a >10 km 3 magma reservoir of evolved basanites (~5 wt % MgO) [14].…”

Special issue Comptes-Rendus Geoscience: The Mayotte seismo-volcanic crisis of 2018–2021 in the eastern Comoros archipelago (Mozambique channel)

“…Knowledge of the geological nature of the surface rocks and deposits constrain possible site effects during seismic shaking [Roullé et al, 2022]. Being prepared and preventing damages in case of seismic shaking can be explored for crisis management [Taillefer et al, 2022]. The unstable submarine slopes of Mayotte could be prone to landslides themselves triggering tsunamis [Poulain et al, 2022].…”