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

• Published in: Comptes rendus. Geoscience Vol. 354; no. S2; pp. 317 - 341
• Main Authors: Roullé, Agathe, Baillet, Marie, Bertil, Didier, Cornou, Cécile
• Format: Journal Article
• Language: English
• Published: Paris Académie des Sciences. Institut de France 01-01-2022; Académie des sciences (Paris); Académie des sciences
• Subjects: Earth Sciences; Earthquakes; Geology; Islands; Lithology; Management of crises; Mapping; Mayotte; Sciences of the Universe; Seismic hazard; Seismic risk; Site effects; Spatial analysis; Topography; Volcanic formations; Weathering; Mayotte; Formations volcaniques; Risque sismique; Altération; Aléa sismique; Effets de site
• ISSN: 1778-7025; 1631-0713; 1778-7025
• DOI: 10.5802/crgeos.151

Since the 2000s, local seismic hazard studies have shown that Mayotte Island presented superficial geological formations prone to lithological site effects. The seismic sequence initiated in May 2018 confirmed the importance of such effects, both in terms of intensity and spatial extension. The analysis of the recorded strong motions showed that weathered volcanic formations are prone to significant site effects with mean amplification factors for peak ground acceleration (PGA) between 1.4 and 4.9 and that a complex combination of lithological and topographic site effects is in action. We thus implement a regional scale map of site effects for the fast calculation of strong motion and damage maps for crisis management purposes. We also provide a first estimate of key site parameters for eight stations: surface geology, resonance frequency, an amplification factor proxy for PGA, a \({V}_{{S},30}\) value, if available, and an estimated EC8 soil class.