Tsu-Memo: November 1, 1755. The Lisbon earthquake and tsunami

«Vidi a un tratto una grossa trave del soffitto non solo muoversi ma girare verso destra e poi tornare, con un movimento lento e ininterrotto, al suo posto... Non dissi nulla, quasi rallegrato da quel fenomeno. Qualche secondo dopo la scossa si ripetè, e non potei più trattenermi dal gridare: Un' altra, un' altra, gran Dio, ma più forte!. Gli arcieri, spaventati dalla mia empia invocazione, fuggirono atterriti...». (G. Casanova diaries)

Screamed Giacomo Casanova, Venetian adventurer and writer (1725-1798), imprisoned since July 1755 in the prison inside the Dogi's Palace, called the Piombi, in Venice, hoping that a new earthquake, stronger, would open a breach in the prison walls allowing him to escape.

It is estimated that the earthquake, which happened on the morning of November 1, 1755, occurred in the Atlantic Ocean, a few tens of kilometers southwest of the city of Lisbon, with a magnitude of about 8.5. Felt in most of Europe, caused damage in an area of about 800,000 km2 and almost totally destroyed the city of Lisbon, where it is estimated that between 25 and 30% of the population lost their lives.

It was probably the biggest seismic disaster in Western Europe, causing about 100,000 deaths considering the damage caused by the earthquake, the effects of the tsunami and the fires that developed in urban areas (Gutscher et al., 2006).

It was not easy to identify the earthquake's seismic source due to the absence of advanced seismic detection instruments and the location of the epicenter in the ocean.

The earthquake generated a devastating tsunami. Numerous texts written by contemporary authors describe the effects that the tsunami caused along the Portuguese and African coasts. The city of Lisbon was seriously damaged by the tsunami, which penetrated inside the city following the Tagus river from its mouth. The tsunami destroyed most of the Algarve coastal towns, south of Portugal, causing widespread damage along the coasts of North Africa while its effects were observed up to the offshoots of the North American continent, in the Caribbean islands and Scandinavian countries.

The Lisbon earthquake stimulated the philosophical debate that characterized the "Age of Enlightenment", where the faith in optimism and in the progress of humanity guaranteed by God and expressed in the essays of Leibniz and Pope, was contrasted by a growing rationalism, theorized by Voltaire and other contemporary philosophers.

The French philosopher, following the catastrophe produced by a natural event of such dimensions, radically changes his opinion and, in his work: Poem on the Lisbon Disaster, he writes about his doubts on the existence of evil as a providential choice of God and rages against the philosophers - whom he defines as fallacious - of "Everything is good". The Poem is sent to Rousseau, who distances himself from Voltaire's pessimistic reading, identifying humans as responsible for the disaster. According to Rousseau, the Lisboners had offended nature and its simplicity by building a prosperous capital city where tens of thousands of people had amassed:

«per esempio, la natura non aveva affatto riunito in quel luogo ventimila case di sei o sette piani, e che se gli abitanti di quella città fossero stati distribuiti più equamente sul territorio e alloggiati in edifici di minor imponenza, il disastro sarebbe stato meno violento o, forse, non ci sarebbe stato affatto.»(Rousseau, 1756).

Even today, Rousseau's consideration keeps its value intact, as we unfortunately have to see after every major earthquake that hits our country.