Observation of a meteotsunami on July 27, 2012 in the Western Mediterranean

 

A mini-tsunami was measured Friday, July 27, 2011 by the French tide gauges at Port-Vendres and Sète. It manifested along the Spanish and French coast as high amplitude oscillations of sea level.

Port de Sète avec son phare (à gauche en arrière plan) et l'observatoire marégraphique (bâtiment à droite de l'image). Crédits SHOM, février 2011

 

Observation of the event by Spanish tide gauges

This mini-tsunami was observed by the French RONIM tide gauge network and the Spanish tide gauge network in the northwestern part of the Western Mediterranean. 20 to 45 cm high port seiches were measured at several locations, probably due to this event. The period of these oscillations was between a few minutes and a few tens of minutes and varied according to the configuration of each port. No seismic activity was reported on the date in question by the relevant bodies so the event may have been gravitational (underwater landslide) or meteorological in origin related to sea states or more likely a high atmospheric pressure gradient, in the case of a meteotsunami. Meteotsunamis are well known in the Balearic Islands and along the Mediterranean coast of Spain, where they are called Rissaga. 

 

Oscillations de hauteurs d'eau filtrées par un filtre passe-haut de fréquence de coupure à 2h – cliquer sur la figure pour l'agrandir

 

Period and amplitude measured by tide gauges

High-frequency oscillations of sea level are visible on the water levels filtered by a high-pass filter to eliminate oscillations at periods longer than 2 hours. The figure shows the oscillations of water level measured by the tide gauges along the coasts of Spain, France and in the Balearic Islands. The amplitude of the oscillations reached 30 cm along the Spanish coast and the Balearic Islands, 45 cm in Port-Vendres and 35 cm in Sète.

 

Carte des stations marégraphiques ayant mesurées les oscillations de hauteurs d'eau. Cliquer sur la figure pour l'agrandir

 

Estimate of the propagation

The meteotsunami appears to propagate from the Valencia region eastward towards the Balearic Islands and north along the Catalan and French coast. The maximum oscillations were measured along the coast of Languedoc Roussillon in Port-Vendres and Sète. In Provence, the oscillations were no longer visible.

 

A similar event was observed by French tide gauges in June 2011 in the English Channel and the Atlantic coast.

 

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References

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