Geoscience Reference
In-Depth Information
Netherlands. The passage time between the “possible”
1
seismic source and Cape
Sao Vicente is esteemed in 6-7 min and in 1 h in relation to Cadiz. In Lagos, the
tsunami arrived about 15 min after the mainshock onset, and the waters first run-
down, then went up 13 feet, causing great destruction mainly in the walls protecting
the city. In Portimao, the waters rising 6 “bra¸as” (fathom) drowned too many peo-
ple. As referred, the biggest impact of the tsunami in the Algarve was in the bay of
Lagos which could no longer accommodate big boats (greater than 45 tones) due to
sediment transport and therefore the Harbour Administration has moved from Lagos
to Tavira. Also the Ria de Faro suffered great changes in its coast line (Faro Beach)
with significant sandy movements altering the deposition (Andrade 1992).
In Madeira and Azores Islands, the tsunami was also felt and caused great dam-
ages in the islands of Terceira (cities of Angra do Heroısmo and Praia da Vit oria)
and Faial (city of Horta) (Andrade
et al.
2006).
In Creston Ferry, near Plymouth, England, the waters raised around 16h:00. Two
boats that were in dry land, one and a half meters from the water were “drowned in
mud” after the tsunami. It took around 8 min for the waters to get back to normal
and for the boats to float again. The tsunami was also felt in the coast of America: in
Antigua, 6,000 km away from Lisbon, the first wave of the tsunami arrived at 19h:30
(Lisbon time). Here, the variations of the water level were felt during two and a half
hours, with the highest wave of about 3.5 m. It was also felt in Recife (Brazil) where
the waves destroyed the fisherman huts.
Pararas-Carayannis (1997) mentions for tsunami heights different values and dif-
ferent consequences: Lisbon - run-up with 6 m height entering inland 20 m, Cas-
cais - destruction of many boats, Peniche - many people killed, Set ubal - the water
reached the 1st floor of buildings, Algarve - run-up of 30 m and many fortresses in
the western portion destroyed, Lagos - the waves went over the top of City-walls
(11 m) and entered the river to a distance of more than half mile carrying vessels
to a great distance, Faro - not affected because of the sandy banks that protected
the town, Guadalquibir - the waters reached Seville, Gibraltar - the waves reach
2 m high, Agadir - waves passed over the fortified walls of the town killing many
people, Martinique - waves rose 1 m.
In summary, run-up was observed first in Gibraltar, Ceuta and Madeira; and run-
down was observed first in Lisbon, Lagos (20 fathom) and Cadiz. This allows the
definition of a source zone running EW to the south of Cadiz with uplifting in the
northern wall.
In distances larger than 1,000 km, the seismic waves caused floods originated by
seiches, the movement of the waters of the lakes, rivers and harbours, in a rhythmic
way. This was observed in Switzerland, England, Scotland, Finland and Sweden.
In Scotland, 2,000 km away, the waters of Lake Lamond oscillated with amplitudes
of more than 60 cm during more than one and half hours. In the Dal river, north of
Stockholm, 3,000 km away, these oscillations were also felt. No other earthquake in
1
The location of seismic source in this case is simply
∼
100 km to the west and is mentioned just
as a reference.
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