Review of the 1755 Lisbon Earthquake Based on Recent Analyses of Historical Observations - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 286

the sedimentology of tsunami events from strong storm surges. 1755 Lisbon tsunami
deposits have been also reported in Cadiz province, Spain (Luque et al. 1999).
Whelan and Kelletat (2005) observed large littoral debris and accompanying
geomorphic features and they speculate about their relationship to a tsunami event
at Cape of Trafalgar, located on the southern Spanish Atlantic coast, 500 km east of
Gorringe Bank. Relative dating of weathering features as well as minor bioconstruc-
tive forms in the littoral zone, suggest the Lisbon tsunami of 1755 AD as the event
responsible for the large deposits described. They consider that tsunami run-up or
wave heights for the Cape of Trafalgar boulders of 14-16 m are conservative values.
Banerjee et al. (2001) also found elements for another tsunami 1,000 years ago.
According to Luque et al. (2002) the presence of washover fan deposits on the inland
margin of the Valdelagrana Spit bar, Cadiz, indicates the occurrence of a high energy
marine event around 2300 cal. year BC. Historical, geomorphological, sedimento-
logical, palaeontological and geochronological data suggest that a tsunami could
have affected the area during Roman times.
In a recent study on the Aveiro lagoon, to the north of Portugal, Sarmento and
Cardoso (2006) realized that the salty water flooding occurred in the Spring of 1756
may have been originated by the accumulation of water that entered the lagoon during
the tsunami of 1755, together with the occlusion of the lagoon caused by the anomalous
tsunami sedimentary process in the sandbank (Mem orias Paroquiais, Aveiro).
New investigations on boulder deposits ( 1 ton) found several west of Lisbon,

and signatures of run-up to 50 m asl in vegetation scars with datings of about 200-
300 years ago. This is another indication for the presence of a tsunami associated
to the 1755 event. But it also gives indications of the occurrence of older tsunami,
about 2400 BC and 6000 BC(?), see Scheffers and Kelletat (2005).

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Fig. 21 Reccurrence rate for events in the most important seismic sources of Portuguese region
(adapted from Rio, 1996)