Cyclones and earthquakes

By Riwan KERGUILLEC et Dominique SELLIER

L’Atlas Bleu / Exploring

cyclone, earthquake, oceanic fronts, vulnerability

The article highlights the physical characteristics and formation mechanisms of tropical cyclones and earthquakes on a global scale. Two maps provide visualization of the concentration zones for each of these phenomena and demonstrate the very high level of exposure of the planet’s oceanic fronts.

Carte planisphère des cyclones par zone océanique

Tropical cyclones are large-scale seasonal weather phenomena (gusts of up to 118 km/h) that count as one of the hazards specific to coastal fronts due to the factors that dictate their behaviour and movement. They are formed at latitudes of between 8° and 30° in one of the six main tropical cyclone basins, above warm oceans (>26°C), therefore, mainly in summer and autumn. They then travel towards coastal areas due to the deflection caused by the Coriolis effect. Given that cyclones are located where the continent meets the ocean and lose power as they move over land due to reduced evaporation, oceanic coastal fronts and islands are seasonally exposed to their direct (high winds, heavy rain, flooding, storm surges) or indirect (landslides) effects.

Planisphère des séismes sur les façades oceaniques

Earthquakes are caused by a strain between two lithospheric plates and are accompanied by a sudden release of energy deep below and at the earth’s surface. Oceanic crust formation at oceanic ridges and its destruction at oceanic trenches are two major global tectonic phenomena that involve extreme mechanical stress, thus leading to high seismic activity. A survey of earthquakes over the last 20 years in countries with oceanic coastal fronts has clearly shown that there are zones of high seismic activity at active plate margins (the Ring of Fire in the Pacific). Earthquakes are therefore one of the most frequent and destructive risks faced by these coastal fronts.

Riwan KERGUILLEC, géographe, est ingénieur de recherche OSUNA, coordinateur de l’Observatoire Régional des Risques Côtiers en Pays de la Loire.

Dominique SELLIER, géographe, est Enseignant-Chercheur à l’Institut de Géographie et d’Aménagment Régional de l’Université de Nantes et à LETG UMR 6554.

Riwan KERGUILLEC, Dominique SELLIER, « Cyclones et séismes », L’atlas Bleu, Revue cartographique des mers et des littoraux. Mis en ligne le 11 janvier 2020,

(version digitale adaptée d’après l’article paru dans L’Atlas Permanent de la Mer et du Littoral n°7 « Risques littoraux et maritimes ». Ed. LETG-Nantes, 2015. p.11)

URL : https://atlas-bleu.cnrs.fr/

DOI : 10.35109/atlasbleu-fr.10025