The earthquake of 4.5 degrees on the Richter scale, according to the National Geographic Institute (IGN) -of 4.2, according to the Cartographic and Geological Institute of Catalonia (ICGC) -, which took place this Wednesday, the largest recorded this century in Catalan soil, has had a hundred small replicas, which have not caused damage either.
As reported by the ICGC, the first replica, of a magnitude of 2.2, occurred five minutes after the earthquake and was not perceived by the population, and all other replicas have had a lower magnitude.
The earthquake was caused by a movement in the African and Eurasian plates at 5:29 pm yesterday with an epicenter in Alt Urgell, although it was perceived in a large part of Catalonia.
The analysis of the seismic recordings has made it possible to obtain the location of the hypocenter -the point of the subsoil where the movement takes place- and calculate the magnitude.
The epicenter - the point of the surface located on the hypocentre - is located between the municipalities of Ribera d'Urgellet, Les Valls d'Aguilar and Montferrer i Castellbò.
In the area closest to the epicenter, the earthquake was felt with stronger intensity (IV-V), while in the metropolitan area of Barcelona and the Camp de Tarragona was perceived with an intensity between II-III, without evidence that it caused no harm.
According to the historical seismic data of Catalonia, each year there are an average of five earthquakes of magnitude greater than 3. Every two and a half years there is an earthquake with magnitude greater than 4, and every 30 years, one more than 5.
The simologists have knowledge of two earthquakes of magnitude higher than 6 during the Middle Ages in the area of La Garrotxa and El Ripollès.
According to the ICGC, seismicity in Catalonia is presented "diffusely", but it is mainly located in the Pyrenees, the Selva and in the coastal zone.
The most recent earthquake that has caused damage (light and moderate in some buildings) was on September 21, 2004 in the Ripollès, of magnitude 4.
The Alt Urgell earthquake recorded yesterday, of magnitude 4.2, is the largest earthquake that has occurred so far in the Catalan western Pyrenees in the 21st century.