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earthquake info
earthquake info
interesting article from the algarve observer web news site today about earth quakes.
It is 250 years since Portugal’s biggest ever natural disaster occurred
The Algarve has cause to shake with fear
10/31/2005 12:20:00 PM
The Algarve is the most vulnerable seismological region in the country. The consequences of an earthquake like that of 1755 would be catastrophic, as shown in a simulation carried out by the LNEC.
About 3% of the population could die and 30% of residential properties would collapse or be seriously damaged, if there was a major earthquake. These figures emerge from a simulation recently carried out by the National Civil Engineering Laboratory (LNEC).
In a total population of 390,000, this study suggests that there would be some 11,000 dead and almost 7,000 injured. About 16,500 buildings would collapse, while over 31,000 would suffer severe damage.
In reality, the numbers could be much more serious as the study is limited by the fact that it does not include a seasonal or demographic component, meaning that the main concentration of Portuguese and foreign tourists during the Algarve’s summer season is not taken into consideration.
Ema Coelho, head of the LNEC’s Centre for Seismic Engineering and Dynamics of Structures told the “Expresso” newspaper that there is a certain margin of uncertainty in the simulation, and that even if there was appreciable material damage and catastrophic and economic losses, even without taking indirect costs into consideration, the number of dead would be lower than on 1st November 1755 (250 years ago), because, despite everything, today’s population is better prepared to deal with a major earthquake and the Civil Protection has done important work.
Furthermore, most specialists argue that, in Portugal, the return period for an earthquake of similar magnitude to that of 1755 – between 8.7 and 9 on the Richter scale – is quite long, in the order of 1,000 years or more.
The origins of the quake are still a mystery
The puzzle about the epicentre of the 1755 earthquake has still not been solved, despite the scientific progress that has been made. Specialists confirm that this will only be done by finding out more about the seafloor between the southwest of the Algarve coast and the Gulf of Cadiz, where almost all the major earthquakes that have hit Portugal in the last 2000 years have originated.
The only thing that is certain for some scientists is that the main rupture that is thought to have caused the catastrophe is located in the Marquês de Pombal fault, 100 kilometres west of Cape St Vincent.
But not on its own. Another suggestion is of a link between the Marquês de Pombal fault and the Ferradura fault, located 140 kilometres south of cape St Vincent, to explain the origins of the biggest natural disaster ever to occur in Portugal.
Luís Matias, of the Faculty of Science in Lisbon, points out that the seismic activity in the zone to the south of the Algarve is linked to the collision between the Eurasian and African tectonic plates, and that the boundary between them is complex. The specialist said that this was why the origin of 1755 has not been found.
Meanwhile, it has been concluded that the faults in the Gorringe Bank, a big underwater mountain 300 kilometres from Cape St Vincent, could not be the origin of the catastrophe as had been previously thought, as it is too far from the Portuguese coast.
Luís Matias stressed the importance of discussion about the issue because they need to know where the 1755 earthquake started in order to determine where the boundary zone between the tectonic plates still has to rupture, which could cause major earthquakes in the future.
It is 250 years since Portugal’s biggest ever natural disaster occurred
The Algarve has cause to shake with fear
10/31/2005 12:20:00 PM
The Algarve is the most vulnerable seismological region in the country. The consequences of an earthquake like that of 1755 would be catastrophic, as shown in a simulation carried out by the LNEC.
About 3% of the population could die and 30% of residential properties would collapse or be seriously damaged, if there was a major earthquake. These figures emerge from a simulation recently carried out by the National Civil Engineering Laboratory (LNEC).
In a total population of 390,000, this study suggests that there would be some 11,000 dead and almost 7,000 injured. About 16,500 buildings would collapse, while over 31,000 would suffer severe damage.
In reality, the numbers could be much more serious as the study is limited by the fact that it does not include a seasonal or demographic component, meaning that the main concentration of Portuguese and foreign tourists during the Algarve’s summer season is not taken into consideration.
Ema Coelho, head of the LNEC’s Centre for Seismic Engineering and Dynamics of Structures told the “Expresso” newspaper that there is a certain margin of uncertainty in the simulation, and that even if there was appreciable material damage and catastrophic and economic losses, even without taking indirect costs into consideration, the number of dead would be lower than on 1st November 1755 (250 years ago), because, despite everything, today’s population is better prepared to deal with a major earthquake and the Civil Protection has done important work.
Furthermore, most specialists argue that, in Portugal, the return period for an earthquake of similar magnitude to that of 1755 – between 8.7 and 9 on the Richter scale – is quite long, in the order of 1,000 years or more.
The origins of the quake are still a mystery
The puzzle about the epicentre of the 1755 earthquake has still not been solved, despite the scientific progress that has been made. Specialists confirm that this will only be done by finding out more about the seafloor between the southwest of the Algarve coast and the Gulf of Cadiz, where almost all the major earthquakes that have hit Portugal in the last 2000 years have originated.
The only thing that is certain for some scientists is that the main rupture that is thought to have caused the catastrophe is located in the Marquês de Pombal fault, 100 kilometres west of Cape St Vincent.
But not on its own. Another suggestion is of a link between the Marquês de Pombal fault and the Ferradura fault, located 140 kilometres south of cape St Vincent, to explain the origins of the biggest natural disaster ever to occur in Portugal.
Luís Matias, of the Faculty of Science in Lisbon, points out that the seismic activity in the zone to the south of the Algarve is linked to the collision between the Eurasian and African tectonic plates, and that the boundary between them is complex. The specialist said that this was why the origin of 1755 has not been found.
Meanwhile, it has been concluded that the faults in the Gorringe Bank, a big underwater mountain 300 kilometres from Cape St Vincent, could not be the origin of the catastrophe as had been previously thought, as it is too far from the Portuguese coast.
Luís Matias stressed the importance of discussion about the issue because they need to know where the 1755 earthquake started in order to determine where the boundary zone between the tectonic plates still has to rupture, which could cause major earthquakes in the future.