An earthquake measuring 4.3 on the Richter scale was felt across the Greater Lisbon area this morning.
The tremor had its epicentre at Sobral de Monte Agraço, near Torres Vedras, and started at 07:44, lasting but a few seconds but was the third one in the past week from the same location.
At 10.15, an earthquake of magnitude 3.1 was registered by Seismic Network stations as having an epicentre about 65 kilometres south-southeast of Tavira.
Experts reassured the public, saying there is no reason for alarm despite today’s earthquake being the most violent for 12 years, as since 1961 there have been 16 earthquakes in mainland Portugal with a magnitude greater than 4.3 on the Richter scale.
The last time an earthquake with a magnitude greater than 4.3 hit the mainland of Portugal was on December 29, 2005 when two earthquakes of magnitudes 4.4 and 4.5 shook the region of Montemor-o-Novo in the Évora area.
According to Fernando Carrilho, the director of the Geophysics Division of the Portuguese Weather Service, an earthquake measuring 6 on the Richter scale, such as that felt in 2009 100 kilometers southwest of Cape St Vincent, "would have terrible effects" if the epicenter was on mainland Portugal.
“It is important to distinguish the differences between magnitude (Richter scale) and intensity (Mercalli scale). While the magnitude refers to the energy released in an earthquake, the intensity refers to its effects at a given location,” said Carrilho.
History
The 1755 Lisbon earthquake, (see picture above) also known as the Great Lisbon earthquake, occurred in Portugal on November 1st, All Saints' Day, at around 09:40.
In combination with subsequent fires and a tsunami, the earthquake almost totally destroyed Lisbon and adjoining areas.
Seismologists today estimate the Lisbon earthquake had a magnitude in the range 8.5–9.0 on the moment magnitude scale, with its epicentre in the Atlantic about 200 kilometres west-southwest of Cape St. Vincent.
Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the deadliest earthquakes in history.
