Review of the 1755 Lisbon Earthquake Based on Recent Analyses of Historical Observations - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 284

Fig. 19 Damage caused to the “Torreao do Terreiro do Pa¸o” and West wing of “Terreiro do Pa¸o”:
a) vertical cracking caused by strong motion and soil settlement (on the left hand side). Damage
due to fire (on the right hand side). b) detail of “Torreao”
5.3 The Liquefaction Distribution and the Sinking
of “Cais das Colunas”
Liquefaction observed throughout the country was another source of important in-
formation. Jorge (1994) showed locations of confirmed and probable liquefaction
at sites near the coastal areas at large distances to the epicentre, denoting the large
amplitude of the event, Fig. 20. According to Ambraseys (1988) only magnitudes
above 9 would originate these phenomena at such large distances.
We should also add that a large number of people that run into the “Cais das
Colunas”, a pier built in front of the Tagus River just before the earthquake, were
drowned due to its collapse. The collapse, previously attributed to tsunami waves,
is now recognized as a liquefaction phenomenon with the sinking of the entire pier
whose foundation was sitting on a muddy sand.