THE 1755 LISBON, PORTUGAL EARTHQUAKE, TSUNAMI, & FIRE

Geographical Background
Lisbon is the capital city of Portugal as well as its largest city. It lies on the coast of the Atlantic Ocean, where the Tagus River and the ocean meet.
Portugal lands between Spain (on the right of it) and the Atlantic Ocean (on the left of it). In addition, the continent of Africa lies below it.


Portugal_Map.gif
The map above shows Portugal lying next to Spain, with the Tagus River flowing through its country. Lisbon, the capital city, lies on the edge of the Portugal, where the Tagus River and the Atlantic Ocean meet.


Previous Natural Disasters
Portugal contains numerous fault lines and lies nearby the Atlantic Ocean which also contains a large amount of faults underwater. Additionally, Lisbon is at the mouth of the Tagus River, which further enhances the hazards of Lisbon, because the lower part of the Tagus River is on top of a fault line. All of these result in the historical earthquakes experienced by Portugal, Spain, Morocco, and other adjacent countries.
Being the capital city that lives on the edge of the Eurasian Plate, which collides with the African Plate, Lisbon experiences constant earthquakes. In the 14th century, Lisbon has eight recorded significant earthquakes, while in the 15th century, it had five recorded large earthquakes.
Because Portugal happens to be on the edge of where the two plates collide, Portugal has a long history of earthquakes, followed by tsunamis and other natural disasters caused by these large quakes.

Although the frequency of these natural disasters is not extremely high, the effects of each event are enormously great. The impacts on the country of Portugal and other close-by nations have resulted in major deaths and damages on the economy. Because of these devastating losses for the country, Portugal began its studies of seismology, hoping that understanding the natural hazards of their location would lower their losses in the future.
Some of the most significant historical disasters that impacted Portugal include the 1531 earthquake (which totaled a loss of roughly 30,000 citizens) and the 2007 earthquake (which measured a 6.1 on the Richter Scale but did not result in any damage or deaths).
Other less tragic events include the 1551 earthquake that collapsed 200 houses and the 1597 earthquake that shook down the buildings of three streets.


The 1755 Lisbon Earthquake, Tsunami, & Fire
On November 1st, 1755, Lisbon faced their greatest natural disaster of their history. At 9:30 am in the morning, an earthquake with an estimated intensity of magnitude 8.7 hit the city. Most of the population was in churches celebrating All Saint’s Day. The majority of the city structures began to collapse, either crushing the city residents inside or trapping them in. The shaking lasted for 9 minutes, one of the longest earthquakes in historical records. In other parts of Portugal, as well as nearby countries such as Spain and Morocco, other cities were also devastated by this natural catastrophe.
Following a few minutes after the earthquake, Lisbon experienced a large tsunami. The citizens that did escape the earthquake had run to the coast to avoid the crumbling buildings, but were ultimately swallowed up by the harbor waves. Effects of the tsunami were said to have been felt all throughout the Atlantic Ocean, impacting western Europe, North Africa, North America, and the Caribbean Islands.
The rest of the city had broken out in fires due to the remains of candles that set off on the debris of the city ruins. The fires lasted for five days and destroyed most of Lisbon, the city capital.
In Lisbon alone, an estimate of 30 to 40 thousand people were killed due to the 1755 earthquake, tsunami, and fire. The number of casualties throughout all of the locations that felt this event added up to an approximation of 90,000 to 100,000 deaths.

Engravings.jpg
Historical engravings displayed the city on fire, shook to shambles, and engulfed by the sea. Citizens are trapped with no where to go.

Origin Hypothesis of the 1755 Lisbon Tsunami

The 1755 earthquake that neared a magnitude 9.0 occurred 200 kilometers from the Portugal coast, in the Atlantic Ocean. In this area, the major fault that exists is the Azores – Gibraltar Fracture, where the Eurasian and African Tectonic Plates collide.
Some believe that the 1969 earthquake that occurred in the Atlantic Ocean had the same epicenter as the 1755 quake, but records say that the travel time from the epicenter to Portugal took 40 minutes during the 1755 quake while the 1969 had a travel time of 50 minutes. Scientists agree that due to the different time lengths, the two earthquakes could not have originated from the same epicenter.
Even until today, the epicenter or origin of the 1755 Lisbon earthquake is still unknown. Because society lacked the technology during 1755, it has been difficult to calculate the exact number of fatalities, injuries, building damages, and so on. However, through the studies of journals and land cores, scientists have been able to formulate hypotheses and estimates.
Many believe that the Azores – Gibraltar Fracture Zone is the cause of the 1755 Lisbon earthquake. Since the east part of the Azores – Gibraltar Fracture separates the Eurasian and African Plates, there is a lot of complex activity that takes place there. The east portion of the fracture is also known as the compression zone, where subsidence occurs. Because the 1755 Lisbon earthquake resulted in a magnitude of 8.5-9.0, theories suggest that the only fault line within the Atlantic Ocean in this area that could impact such a great natural disaster is the Azores – Gibraltar Fracture.
Due to the subsidence of one plate under another, the sea waters become displaced. The small waves become large harbor waves as they near the coast, because the ocean dept decreases near land. As the ocean level becomes shallower, the sea floor pushes the waves higher into the air, creating the monstrous 1755 Lisbon tsunami that took part in becoming Europe’s greatest natural disaster of its history.


Influences on Technology
Experiencing such a tragic natural disaster that caused numerous deaths and great economic loss, Europe took immediate action and began their first researches into seismology. As Europe become more educated and technologically advanced, their awareness of natural hazards allowed them to prevent the same events from repeating. Today, there are many ways to communicate early alerts to the public about potential natural disasters. In addition, there are better building codes in urban cities to help buildings withstand these hazards.



Resources
About.com. "Lisbon Earthquake, 1 November 1755." <http://geology.about.com/od/historicearthquakes/Historic_Earthquakes.htm>
Holmes, Oliver Wendell. Updated Mar 2008.Viewed Nov 2008. <http://www.phenomena.org.uk/>
Kozak, Jan T., and James, Charles D. Updated Nov 1998. Viewed Nov 2008. http://nisee.berkeley.edu/lisbon/
Pararas-Carayannis, George. "The Great Lisbon Earthquake and Tsunami of 1 November 1755." Updated 2000. Viewed Nov 2008. <http://www.drgeorgepc.com/Tsunami1755Lisbon.html>
Pereira, Alvaro S. The Opportunity of a Disaster: The Economic Impact of the 1755 Lisbon Earthquake. Cherry Discussion Paper Series: Mar 2006. Viewed Nov 2008. <http://www.york.ac.uk/res/cherry/docs/Alvaro3.pdf>
Risk Management Solutions WebPage. <http://www.rms.com/Catastrophe/Models/Portugal.asp>
Tilling, Heliker, and Wright. United States Geological Survey WebPage. Updated 1997. Viewed Nov 2008. <http://vulcan.wr.usgs.gov/>
United State Geological Survey WebPage. Updated July 2008. Viewed Nov 2008. <http://earthquake.usgs.gov/regional/world/>
Wynn, Russell. Updated April 2002. Viewed Nov 2009. <http://www.science.soton.ac.uk/science_news/current_issue/>