1693 Sicily earthquake
The 1693 Sicily earthquake struck parts of southern Italy near Sicily, Calabria, and Malta on 11 January at around 21:00 local time.[1] This earthquake was preceded by a damaging foreshock on 9 January.[7] The main quake had an estimated magnitude of 7.4 on the moment magnitude scale, the most powerful in Italian recorded history,[8] and a maximum intensity of XI (Extreme) on the Mercalli intensity scale, destroying at least 70 towns and cities, seriously affecting an area of 5,600 square kilometres (2,200 sq mi) and causing the death of about 60,000 people.[5][6]
Local date
11 January 1693
4 minutes
7.4 Mw
37°18′N 15°06′E / 37.3°N 15.1°E[3]
The exact location of the epicentre remains uncertain
5–10-metre high waves devastated the coastal villages on the Ionian Sea and in the Straits of Messina. (Ambraseys-Sieberg intensity V tsunami)
A magnitude 6.2 on 9 January[5]
60,000 deaths[6]
The earthquake was followed by tsunamis that devastated the coastal villages on the Ionian Sea and in the Straits of Messina.[9] Almost two-thirds of the entire population of Catania were killed.[5] The epicentre of the disaster was probably close to the coast, possibly offshore, although the exact position remains unknown. The extent and degree of destruction caused by the earthquake resulted in the extensive rebuilding of the towns and cities of southeastern Sicily, particularly the Val di Noto, in a homogeneous late Baroque style, described as "the culmination and final flowering of Baroque art in Europe".[10]
According to a contemporary account of the earthquake by Vincentius Bonajutus, published in the Philosophical Transactions of the Royal Society, "It was in this country impossible to keep upon our legs, or in one place on the dancing Earth; nay, those that lay along on the ground, were tossed from side to side, as if on a rolling billow."[1]
Tectonic setting[edit]
Sicily lies on part of the complex convergent boundary where the African Plate is subducting beneath the Eurasian Plate. This subduction zone is responsible for the formation of the stratovolcano Mount Etna and considerable seismic activity. Most damaging earthquakes however, occur on the Siculo-Calabrian rift zone. This zone of extensional faulting runs for about 370 kilometres (230 mi), forming three main segments through Calabria, along the east coast of Sicily and immediately offshore, and finally forming the southeastern margin of the Hyblaean Plateau. Faults in the Calabrian segment were responsible for the 1783 Calabrian earthquakes sequence.[11]
In the southern part of the eastern coast of Sicily, investigations have identified a series of active normal faults, dipping to the east. Most of these lie offshore and some control basins that contain large thicknesses of Quaternary sediments. The two largest faults, known as the western and eastern master faults, border half-grabens with fills of up to 700 metres (2,300 ft) and 800 metres (2,600 ft) respectively. Onshore, two ages of faulting have been recognised, an earlier phase trending NW-SE and a later phase trending SSW-NNE that clearly offsets the first group, including the Avola fault and the Rosolini-Ispica fault system.[12]
Tsunami[edit]
The tsunami triggered by the earthquake affected most of the Ionian Sea coast of Sicily, about 230 kilometres (140 mi) in all. The first thing that was noted at all localities affected was a withdrawal of the sea. The strongest effects were concentrated around Augusta, where the initial withdrawal left the harbour dry, followed by a wave of at least 2.4 metres (7.9 ft) height, possibly as much as 8 metres (26 ft), that inundated part of the town. The maximum inundation of about 1.5 kilometres (0.93 mi) was recorded at Mascali.[15]
Tsunami deposits linked to the 1693 tsunami have been found both onshore and offshore. At Ognina, just south of Syracuse, at the head of a ria, a sequence containing several coarse clastic layers has been found, inconsistent with its lagoonal setting. The uppermost coarse layer, which has a strongly erosive base, consists of coarse sand with up to granule size clasts. The layer has been dated as 17th to 18th century based on pottery shards and one well-preserved clay pipe, consistent with the 1693 tsunami.[16] Offshore from Augusta, a sequence identified using chirp sonar data was sampled with a 6.7 metres (22 ft) gravity core in 72 metres (236 ft) of water. Following detailed analysis of both grain size and foraminifera assemblages, eleven possible high-energy events were found based on the presence of large numbers of shallow water forams combined with a greater proportion of fine sand in the same interval. The uppermost two events correlate well with the tsunamis from the 1908 Messina earthquake and the 1693 earthquake.[17]
Link to eruption of Etna[edit]
Although there are reports of an eruption at the time of the earthquake, most sources suggest that the volcano had been inactive since the destructive eruption of 1669. Analysis of the relationship between eruptions and earthquakes has found that earthquakes are followed by long periods without activity in the 'rift zones' that extend out to north and south from the summit. Estimates of Coulomb stress transfer due to the dyke intrusion in the rift zones associated with the 1669 eruption, suggest that this could have helped to trigger the 1693 earthquake, by increasing stress levels on the faults.[18]