The Effects of the 1755 Lisbon Earthquake and Tsunami on the Algarve Region, Southern Portugal

Article excerpt

ABSTRACT:

The 1755 Lisbon earthquake (magnitude c. 8-5Mw) killed between 15,000 and 20,000 people, of whom an estimated 1020 lived in the Algarve. The earthquake cost Portugal between c. 32 and 48% of its Gross Domestic Product, probably making it financially the greatest natural catastrophe to have affected western Europe. Using a combination of archival information and data collected in the field, this article discusses the devastating effects of the earthquake and tsunami on the economy, society and major settlements in the Algarve, and the recovery of the region in the years that followed. Today the Algarve is one of Europe's principal tourist destinations and a region vital to the Portuguese economy. The 1755 earthquake was not a one-off event and the Algarve, which now houses a resident population of over 400,000 - a figure that more than doubles with tourists in the summer months - is highly exposed to earthquakes and tsunamis. An earthquake of similar size (minimum estimated recurrence 614±105 years), is viewed as a worst-case future scenario. Although strict building codes which apply to the whole country were pioneered in Portugal following the 1755 earthquake, and have been revised on many occasions, there is a recognised need for more detailed hazard maps and emergency plans for the Algarve. These have already been produced for Lisbon and in the Algarve a start has been made, where a tsunami risk map has recently been completed for Portimão concelho1 (i.e. county).

Introduction

On Sunday 26 December 2004 the countries bordering the Indian Ocean were devastated by the fourth largest earthquake to have affected the world since 1900, and the highest magnitude event since Prince William Sound in Alaska was struck in 1964. The epicentre was located 225km south-south-east of Banda Aceh in Sumatra (Indonesia) and the earthquake had a moment magnitude (Mw - see glossary) of c. 9.0. Official tallies estimate the number of deaths at over 180,000, and a few months later more than 230,000 people in some 12 countries were still unaccounted for. More than 1.7 million people had lost their homes (Shepard, 2005; USGS, 2007).

It is easy to forget that western Europe has also suffered the effects of major earthquakes and that the greatest disaster to have befallen the region occurred just over 250 years ago when the Lisbon earthquake not only destroyed about a third of the buildings in Portugal's capital city, but also devastated much of southern Iberia and north Africa (Figure 1), with the effects of the related tsunamis being felt with decreasing force as far away as the Caribbean and the British Isles (Degg and Doornkamp, 1994). Comprising three main shocks and many aftershocks, the duration of ground-shaking in Lisbon was c. 10 minutes and, although estimates vary, it is likely that the earthquake's magnitude was at least 8.5 (Mw). It affected an area of c. 800,000km^sup 2^, through a combination of earthquakes and tsunamis (Kozák and Thompson, 1991; Tiedemann, 1991, p. 23). In recent years estimates of death have been reduced as more reliable historical data have been analysed. In the past, many textbooks quoted figures of 40-70,000 (e.g. Bolt, 1999), but the total number of deaths in Portugal probably did not exceed 12,000 from all causes (i.e. earthquake, tsunami and fire). Of those who died c. 10,000 lived in Lisbon. Many victims resided in Spain and Morocco, but in the latter case there is some confusion in both Arabic and European sources between the event of 2 November and the effects of local earthquakes which occurred on 18 and 27 November (Levret, 1991). For Portugal, Spain and Morocco as a whole a mortality figure of 15-20,000 has been proposed (Martínez-Solares and López-Arroyo, 2004), of whom an estimated 1020 resided in the Algarve (Costa et al., 2005). Estimates vary, but taking the population of Lisbon as 150,000 (Marques, 1976), a mortality statistic of c. 10,000 for Lisbon represents c. …