Geoscience Reference
In-Depth Information
nity (Martinez-Solares 2000). Coelho (2007), in studying the possible origins of
both inquiries, classifies this accomplishment as the first scientific quantification of
earthquake damage in history.
Based on the inquiries of the Marquis of Pombal and of the “Memorias Paro-
quiais” (Parish Memories), Pereira de Sousa (1919-1932) compiles a remarkable
amount of information about the damages occurred in the construction and mainly
in the monuments, developing at the same time maps of Mercalli Intensities, as-
signed in different geographical scales, but always with a strong connection with
the geological units in which they were built. For Lisbon, Pereira de Sousa works
with the map drawn by Filipe Folque in a scale of 1:10,000, identified the location
of the existing monuments and classified them by damage classes.
In 1986, Oliveira tried to systematise the information about the damages occurred
in the monumental constructions by the time of the earthquake. Using a wide bibli-
ographic list, with special incidence on the work of Pereira de Sousa, he builds up a
new file of information and presents a new classification of the damages. His work
is supported in traditional methods of organization and registration made on cards
and manual charts using the same cartographic base of Pereira de Sousa.
All this work is now under a final revision, with a transfer of treatment to mod-
ern tools of Geographical Systems of Information (GIS) to proceed to an accurate
location of the monuments worked in the 1980s (San-Payo
et al.
2005) and with
the possibility to easily correlate the class and degree of damage for each structural
typology with other local parameters, such as geotechnical strata, soil frequency,
topography, etc.
3 Description of the Earthquake
The earthquake of 1755, better known as “Terramoto de 1755”, is considered as the
biggest earthquake historically known. It was strongly felt in Lisbon, Algarve, South
of Spain and Morocco. Although without causing any damages, it also left signs of
its occurrence in almost all Europe and in the Azores and Madeira Islands.
The seismic activity during the years that preceded the great quake of November
1st, 1755 was not intense, although references can be found to small quakes from
1750 (the day King John V died). It is interesting to note (National Archive of Torre
do Tombo) that “the day before, meaning October 31st, something happened that
pre-announced this catastrophe. I am referring to the fact that, during that day, the
tide was delayed in more than two hours, fact that was noticed by a pilot, who,
noticing the same during December 10th, shouted throughout Lisbon for people to
stay out during that night because another earthquake could happen”. This prophecy
seemed to be accurate, and if so a good sign of immediate foreshock, as a similar
observation was made on the eve of December 11th, when the earth trembled twice,
violently at 4h:55 in the morning.
On November 1st 1755, Saturday, the weather was too hot for the epoch, with a
temperature of 14
◦
C and a weak wind from NE. The main shock happened at 9h:40
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