01 November 2005

The Earthquake That Changed Europe

The Great Lisbon Earthquake

Two hundred and fifty years ago, at about 9:20 in the morning on All Saints Day, 1755, a magnitude 8+ earthquake occurred, a rupture on the Azores-Gibraltar fracture zone in the Atlantic off the coast of Portugal. The city of Lisbon, the heart of the Portuguese empire and arguably the richest city in Europe, was ruined. Most of the buildings were destroyed, either by the quake itself, by the following fires (which burned for three days), or by the tsunami that surged up the River Taugus half an hour after the earthquake.

Why Lisbon?

Africa rides on one of Earth's great crustal plates, which is slowly moving north. Europe sits on another plate, which is in the way. As the African plate crunches into the Eurasian one, stresses build up. From time to time these stresses cause sudden slips along fault lines (like the one shown in red on the map above), which is what we call an earthquake. (Check here to see animations of the movement of these plates over the eons.) This site on "plate tectonics" shows why earthquakes occur where they do, like the recent one in Kashmir, where the Indian plate is ramming into the Eurasian plate.

Economic Impact

Between 70,000 and 90,000 people were killed in Lisbon, then a city of about 250,000 population. Another 10,000 died in Morocco, also hard hit by the quake. The shaking was felt as far away as the Baltic, and the tsunami reached Britain and North America (although it was only about one meter high by the time it arrived on those distant shores -- in Lisbon it was about six meters high). It is said that the temblor was strong enough in Paris to cause churchbells to ring.

In addition to the loss of life and the destruction of buildings and infrastructure, countless artworks, precious books and manuscripts, and historical records were lost. Lisbon was a rich imperial city (built on the wealth of Portugal's trade in spices -- see related article, slaves from Africa, and gold from Brazil). This Wikipedia article details the destruction. Portugal's days as a leading trading empire with outposts in Asia, Africa and America were already over by 1755, though its colony in Brazil continued to generate wealth. But the ruin of the imperial capital, and the cost of reconstruction, was a further blow to Portugal's status as a great power.

It also affected Portuguese politics of the period. Prime Minister Sebastião de Melo (later Marquis of Pombal), a commoner, took charge and responded effectively after the earthquake (perhaps the first comprehensive disaster response). His power grew, which was a blow to the nobles who had opposed him before the quake. Their opposition festered, and led to subsequent upheaval with the attempted assassination of the King Joseph I, de Melo's patron.

Intellectual Impact

1755 was during the "age of enlightenment" in Europe, a period when rationalism, empiricism and science were beginning to lay the foundations for the modern world. Thus the Lisbon quake was the first in the West to be subjected to scientific inquiry -- the beginnings of seismology. For example, questionnaires were sent to all the parish priests in Portugal to gather information on the local character and impact of the quake. These responses are still archived and used by modern siesmologists. This was the first systematic effort to quantify the effects of an earthquake geographically -- to understand what had happened.

The enormity of the quake profoundly affected many European intellectuals. Immanuel Kant published three works on the quake, drawing on available reports and information, and developing the first modern theory of the causes of earthquakes -- one attributing them to natural rather than supernatural causes.

Just as the 20th century had to come to terms with the Holocaust, so 16th century Western philosophers had to try to understand the great Lisbon earthquake. How could God have permitted such a tragedy, the loss of so many innocent lives, and on a high holy day, just as the faithful were assembling in the churches and cathedrals of Lisbon! The Essais de Théodicée sur la bonté de Dieu, la liberté de l'homme et l'origine du mal of Leibniz (1710) had been an attempt to explain the existence of evil in a world controlled by a benevolent God. Other philosophers objected to this view, in particular Voltaire, who used the tragedy of Lisbon to ridiculeucule Leibnitz's ideas. In his Candide (1759) he places his heroes in Lisbon during the earthquake, after which
. . . Pangloss endeavored to comfort them under this affliction by affirming that things could not be otherwise that they were. "For," said he, "all this is for the very best end, for if there is a volcano at Lisbon it could be in no other spot; and it is impossible but things should be as they are, for everything is for the best."

Disasters Yet To Come

Lisbon had been hit by a significant earthquake in January of 1531, when thousands died. Although the 1755 quake is being commemorated today, are the people of Lisbon, or any other earthquake-exposed city, ready for the next one?

Here is another interesting site on the Lisbon quake.

The image is in the public domain, from Wikipedia Commons, more info here.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

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1 comment:

Gustavo Rocha said...

I can say they are, somewhat. I live in Lisbon and all the major structures have been constructed bearing in mid the seismic characteristics of the city. Nevertheless, time after time, after decades of perhaps over-regulation in terms of engineering, some other decades of under-regulation have came through, followed by yet some other decades of over or under regulation, depending on the political regime being less or more economically liberal. Despite of that nowadays most urban people in Portugal are living in steel reinforced concrete buildings.