A magnitude 3.5 earthquake woke part of the Alentejo at 3.08am
The epicentre sat about 18 kilometres east of Odemira. Ourique felt it most strongly, at intensity IV, with weaker shaking in Almodôvar and Santiago do Cacém. No damage was reported.
It happened at 3.08 on Monday morning. Portugal’s institute for the sea and atmosphere, the IPMA, recorded a magnitude 3.5 earthquake with its epicentre roughly 18 kilometres east of Odemira, in the Beja district. No injuries and no damage have been reported.
The shaking reached a maximum intensity of IV on the modified Mercalli scale in the Ourique council, and was felt more faintly in Almodôvar and in Santiago do Cacém, across the line in the Setúbal district.
What intensity IV means
The two scales are worth separating, because they measure different things. Magnitude describes the energy released. Intensity describes what people actually felt, and it falls off with distance from the epicentre.
Grade IV is a quake that is widely felt. Hanging objects swing, windows and crockery rattle, parked cars rock, and the vibration feels like a heavy lorry going past. It is enough to wake someone and to give them a fright, but it sits below the threshold that normally causes structural damage — which is why the fire services had nothing to log.
Tremors on the southwest coast
The region is no stranger to this. Southwest Portugal lies relatively close to the Azores-Gibraltar fracture zone, where the African and Eurasian plates meet, and low to moderate quakes are recorded there routinely without ever becoming news.
The IPMA said it will issue further statements if the situation warrants. Updated seismological data, including the past few hours of records, is published on the IPMA portal — worth bookmarking if you live in the area, since the official bulletin almost always lands before social media does, and without the embellishment.
The same institute also put four inland districts under a yellow heat warning today, on a day when it is working two fronts at once.
Photo: Vitor Oliveira / Wikimedia Commons (CC BY-SA 2.0)
