Friday, January 22, 2010

Earthquakes in Haiti

I discovered an old book, Geologie d'Haiti, that I bought in Haiti around 1981. It appears to be a textbook for an introductory geology course. In light of recent events the section on seismology was interesting. It begins with a brief description of a seismograph and a definition of earthquakes in general, then gives a description of earthquake damages to be expected according to the Rossi-Forel scale. The language is a little quaint, translated from French.

There are devices for recording earthquakes. They are seismographs, which are essentially a sheet of paper wound on a cylinder that rotates. A needle draws a line on the cylinder. In times of calm, this is a straight line, but when the earth trembles, it becomes sinuous.
Earthquakes, like volcanoes, are due to internal operations of the globe. Earthquakes correspond to ruptures of equilibrium in different compartments of the earth.

Degree one and two: shaking recorded by some devices.
Degree three: tremors felt by people at rest.
Degree four: tremors recorded by all, with noise from doors and windows (shaking).
Degree five: in addition to previous effects: cracking ceilings, furniture oscillating.
Degree six: sleepers are awakened by the uproar and clock pendulums stop.
Degree seven: the walls have cracks.
Degree eight: old houses topple and contents are damaged.
Degree nine: panic -- buildings collapse and oscillate. Fires.
Degree ten: complete disaster: the destruction of buildings, bridges, drying up of wells.
Degree Twelve: uplift and subsidence of parts of mountains, breaking land, complete destruction.

Then it goes on to give a history of seismic events in Haiti from 1701 to 1953.
Quelques tremblements de terre historiques d'Ha'iti Some earthquakes of historic Ha'iti

In his book "Geology of the Republic of Haiti " (1924), the American geologist Wendel Woodring writes: " Earthquakes are frequent in Haiti. At the time of the colony and of the Republic, disastrous earthquakes, from time to time, have caused the complete or nearly complete destruction of Port-au-Prince, Cap-Haitian, and other cities."

Indeed our country is often the seat of earthquakes whose disastrous consequences are intensified in the cities because they are generally built on alluvial land (soft ground).

November 9, 1701. It caused the destruction of the plain Leogane (degree VI).
From November 21, 1751 to December 8, Port-au-Prince, which had just been founded, undergoes a series of shocks. It is reported that after the first shock of November 21, one house remained standing, but was in turn destroyed by the earthquake that took place on the second day (degree VIII and IX).
June 3, 1770. New quake Port-au-Prince, in the plain of Cul-de-Sac. 200 deaths in the city of Port-au-Prince. Petit-Goave and Leogane were destroyed (IX degree).
May 7, 1842. One of the most violent. It completely destroyed the cities of Cape Ha'itien, Port de Paix and Mole St. Nicolas. There were 5000 deaths in the city of Cap Haitien alone, and no building was left standing in Port de Paix (degree X).
April 8, 1860. It was felt throughout the whole southern peninsula. (V degree).
September 23, 1887. It spared nothing in Mole St. Nicolas, and its effects were felt very far to South (Jérémie, Anse-d'Hainault) (IX degree).
March 20, 1910. It shook the whole North and North-West of the country causing extensive damage (degree IV).
August 3, 1910. The whole Republic was shaken, but with a particularly marked effect in Jérémie (VII degree).
August 21, 1911. The whole country was shaken with different intensities. Gonaives, Mole St. Nicolas, Pilate, Cap-Haitien. Gros Morne were the cities hardest hit (VIII degree).
October 6, 1911. The shock was particularly strong in Puerto Rico and Dominican Republic, but it seriously damaged the city of Cerca La Source (degree X).
6 and September 7, 1912. It was general, but particularly reached the towns of Plaisance, Limbe, Grande-Riviere-du-Nord and St-Michel de I'Atalave (degree. VIII).
July 31, 1914. Very intense shock affecting Port-au-Prince and its environs. It lasted 50 seconds (VII degree).
July 26, 1917. Very strong shaking in Port-au-Prince, Cap-Haitien, Limonade (degree VI).
4 February 1918. It caused partial destruction of the Mole St. Nicolas (degree VII).
From 1909 to 1920. Several series of shocks, fortunately weak one, recorded at I'Anse-a-Veau (level III).
January 15, 1922. Quake which shook all the southern peninsula: from Jeremie to Port-au-Prince and from Jacmel to Cayes. (degree VI).
1953. L'Anse-a-Veau is again the seat of a series of tremors, but their effects are fairly localized (degree IV to VII).

Thus we see that things had been fairly quiet there for the last fifty years. Amid their many other problems and other disasters, most people had forgotten that threat from earthquakes was still a danger. On the scale given above, it looks as if the quake this month was a ten. Interesting that they don't have an eleven; at that level of destruction the details are moot.

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