On a day like today in 1693, a powerful earthquake destroyed parts of Sicily, Calabria and Malta and The Grandma has wanted to remember it.
The 1693 Sicily earthquake struck parts of southern Italy near Sicily, Calabria, and Malta on January 11 at around 21:00 local time. This earthquake was preceded by a damaging foreshock on January 9.
The main quake had an estimated magnitude of 7.4 on the moment magnitude scale, the most powerful in Italian recorded history, 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 and causing the death of about 60,000 people.
The earthquake was followed by tsunamis that devastated the coastal villages on the Ionian Sea and in the Straits of Messina. Almost two-thirds of the entire population of Catania were killed. 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 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.
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.
More information: Visit Sicily
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, 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.
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 and 800 metres 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.
A destructive earthquake occurred two days before the mainshock at 21:00 local time, centered in the Val di Noto. It had an estimated magnitude of 6.2 and a maximum perceived intensity of VIII–XI on the Mercalli intensity scale.
Intensities of VIII or higher have been estimated for Augusta, Avola Vecchia, Floridia, Melilli, Noto Antica, Catania, Francofonte, Lentini, Scicli, Sortino and Vizzini. Augusta lies well outside the main zone of severe shaking; its extensive damage is probably due to its construction on unconsolidated sediments.
From the shape and location of the area of maximum damage, this earthquake is thought to have been caused by movement on the Avola fault.
More information: Visit Calabria
The earthquake lasted for four minutes, according to contemporary accounts. The estimated magnitude of 7.4 is taken from the extent and degree of the recorded damage, with a very large area that reached X (Extreme) or more on the Mercalli scale. The maximum shaking reached XI in the towns of Buscemi, Floridia, Melilli, Occhiola and Sortino.
The source of the January 11 earthquake is debated. Some catalogues give an onshore epicentre without any direct association with a known structure, while others propose that the source was offshore due to the associated tsunami, involving either rupture along a normal fault, part of the Siculo-Calabrian rift zone, or rupture along the subduction zone beneath the Ionian Sea.
An analysis of the distribution of tsunami run-ups along the coast suggests that a submarine landslide triggered by the earthquake is the most likely source, in which case the tsunami provides no constraint on the epicenter. A landslide origin is supported by the observation of possible landslide bodies along the Hyblean-Malta escarpment.
Historic documents in the Archivo General de Simancas mention dozens of aftershocks, some as late as August 1694, and some reportedly as strong as the initial quake of January 11, 1693. Aftershocks continued until at least 1696, with their effects concentrated in towns along the coast, supporting an epicenter either near the coast or offshore.
The tsunami triggered by the earthquake affected most of the Ionian Sea coast of Sicily, about 230 kilometres 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 height, possibly as much as 8 metres, that inundated part of the town. The maximum inundation of about 1.5 kilometres was recorded at Mascali.
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.
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.
The initial reconstruction efforts concentrated on restoring the military defences of Syracuse, Augusta, Catania and Acireale, due to their strategic importance. The reconstruction plans were of three types: move the town to a new site, rebuild at the same site with a completely new town plan or rebuild using the existing town plan.
Examples of towns that fell in the first category were Avola and Noto, their former locations now being known as Avola Antica and Noto Antica. Catania is an example of a city that was rebuilt on the same site to a new plan, while adapting some of the existing structures.
Syracuse is an example of a city rebuilt entirely to its existing plan. Ragusa was partly rebuilt on its old site to the medieval plan (Ragusa Ibla) and partly on a new, but neighbouring site, to a modern plan (Ragusa Superiore).
The degree and extent of the damage caused by the earthquake prompted an architectural revival in the towns of Sicily and Malta, a style that has become known as Sicilian Baroque. At this time many of the palazzi, public buildings, cathedrals and churches were reconstructed in this style.
Towns that suffered serious damage from the earthquake in which many of their structures were rebuilt, include Syracuse, Ragusa, Catania, Caltagirone, Palazzolo Acreide, Modica, Comiso, Scicli and Mdina on Malta. Many of these towns now form part of the UNESCO World Heritage Site Late Baroque Towns of the Val di Noto (South-Eastern Sicily), inscribed in 1992, referring to the exceptional quality of the region's art and architecture.
More information: Visit Malta
from earthquake records,
it became obvious that the problem
could not be reduced to a single peak acceleration.
In fact, a full frequency of vibrations occurs.
Charles Francis Richter
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