Geoscience Reference
In-Depth Information
This means that the first 5% of victims were increased to 10% due to the injuries. In
Lagos many large and small churches were destroyed by the strong shaking. Only
one (Sao Sebastiao) out of 5 or 6 large churches had minor damage. Also, the town
walls facing the ocean and fortresses in the beach were greatly damaged.
In Oporto, 300 km to the north of Lisbon, very little damage was observed (Rosas
da Silva 1939).
In Madeira Island the tower of the Cathedral (Se) fall off to the south over
the “Capela-Mor”. In the Northern coast the tsunami caused first a run-down of
100 m. Then, the run-up flooded the villages of San Vicente, Ponta Delgada and
Porto Moniz. There still exist some speculation on the formation of the Faja,
a place where many people may have died (Baptista, personal communication,
UAveiro 2004).
Claudio da Concei¸ ao (1829) presented some complementary data worth men-
tion. Around the so-called Greater Area of Lisbon there has been quite severe
damage in locations like Sintra, Cascais, Ericeira, etc. The great Convent in Mafra
did not suffer much, neither Alcoba¸a, even though in this one water feeding the
monastery disappeared during a few days. To the north of the country the shaking
was less felt. In Coimbra there were several ornamental objects that fall from their
top walls. Also, the bells sound in the University tower and the river waters became
very agitated. In Madrid the duration was about 8 min. The shaking was felt and in
two situations the fall of the front wall in churches took place.
To the above numbers we should add the tremendous economic impact caused
by the earthquake, which is also a matter of great uncertainty. Values vary from as
low as 40% of the Portuguese GDP to values that can add up to 3-4 times. Twenty
percentage were attributed to the losses from the collapse of the new buildings in
“Terrreiro do Pa¸o”, another 20-30% to losses of stocked goods of high value,
20-30% to the housing stock, and 20% to the monumental structures in general.
In a recent paper, Pereira (2005), after studying new archival and existing data
concludes that direct losses from the earthquake were much lower, of the order
of 40-60% of the Portuguese GDP, but the indirect consequences in the years that
follow the event were major for the economical situation. “In the long-term, in spite
of the terrible casualty toll and significant wealth losses, the 1755 earthquake was
beneficial to the economy”. In contrast, for Spain the total losses may represent
as much as 20% GDP, 5% of which could be attributed to the tsunami damage
(Martinez-Solares 2000).
5 Information from the Behaviour of Simple Structures:
The Inverse Problem
To obtain more precise information to determine a few parameters of ground motion
felt in various sites and to contribute to the establishment of the seismic source of
this event in a more convincing way, we should use the most varied pieces of data.
Besides the distribution of damage which is translated into the isoseismal map, the
tsunami effects on the coastal areas and harbours, the behaviour of simple structures,
Search WWH ::
Custom Search