Today, The Grandma has been reading about one of her greatest passions: Naples. She has learnt more things about the earthquake that occurred in Pompeii and Herculaneum on a day like today AD 62.
On 5 February AD 62, anearthquake of an estimated magnitude of between 5 and 6 and a maximum intensity of IX or X on the Mercalli scale struck the towns of Pompeii and Herculaneum, severelydamaging them.
The earthquake may have been a precursor to the eruption of Mount Vesuvius in AD 79, which destroyedthe same two towns.
The contemporary philosopher and dramatist Seneca the Younger wrote an account of the earthquake in the sixth book of his Naturales quaestiones,entitled De Terrae Motu (Concerning Earthquakes).
The epicentre of the earthquake lies within a zone of active extensional faulting, but close to the southern flank of Vesuvius. Analysis of focal mechanisms from the area around Vesuvius indicates that active faulting in the area involves NW-SE and NE-SW trending oblique-slip normal faults and E-W trending normal faults, part of the zone of active extension that extends the full length of the Apennines mountain chain, associated with continued opening of the Tyrrhenian Sea.
An association between earthquakes in the central Apennines and eruptions of Vesuvius has been proposed, but is not yet proven.
There is some uncertainty regarding the year of this earthquake. Seneca, who was writing soon after the event, describes the earthquake as occurring during the consulship of Memmius Regulus and L. Virginius Rufus, which would suggest the year was AD 63. In contrast Tacitus, who was writing some forty years later, describes it as occurring during the consulship of P. Marius Celsus and L.Asinius Gallus, which indicates AD 62. The page for this event in the online Catalogue of Strong Earthquakes in Italy (BC 461-1977) discusses this discrepancy and considers that AD 62 is the more likely date.
The extent of damage has been used to estimate the magnitude of the earthquake. Estimates lie in the range from about 5 to 6.1. The maximum felt intensity is estimated to have been in the range IX to X, and the area of highest intensity was elongated roughly WNW-ESE. Shaking was reported to have continued for several days, presumably referring to a sequence of aftershocks. The focal depth is estimated to have been in the range 5–6 km.
The earthquake is likely to have been a precursor to the renewed activity of Vesuvius in AD 79, following a long dormant period.
The towns of Pompeii and Herculaneum both suffered major damage, with damage to some buildings also reported from Naples and Nuceria. Seneca reported the death of a flock of 600 sheep that he attributed to the effects of poisonous gases.
The damage caused by the mainshock and the subsequent series of tremors was at least partly repaired in both Pompeii and Herculaneum by the time of the AD 79 eruption. A pair of bas-reliefs, probably from the lararium in the house of Lucius Caecilius Iucundus in Pompeii, are interpreted as depicting the effects of the earthquake on structures including the Temple of Jupiter, the Aquarium of Cesar, and the Vesuvius Gate.
The earthquake led Roman philosopher, statesman and dramatist Seneca the Younger to devote the sixth book of his Naturales quaestiones to the subject of earthquakes, describing the event of 5 February and giving the cause of earthquakes as the movement of air.
As seismologists gained more experience 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.
Today, The Grandma is still relaxing at home. The weather is better but not enough to go out and enjoy the city. She has been reading about one of her favourite themes, the earthquakes.
On a day like today in 1693, a powerful earthquake destroyed parts of Sicily, Calabria and Malta and TheGrandma 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 coastalvillages 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 culminationand 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.
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.
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.
Offshore from Augusta, a sequence
identified using chirp sonar data was sampled with a 6.7 metres gravity
core in 72 metres 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.
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 exceptionalquality of the region's art and architecture.
As seismologists gained more experience 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.
An earthquake is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves.
Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.
An earthquake may cause injury and loss of life, road and bridge damage, general property damage, and collapse or destabilization (potentially leading to future collapse) of buildings. The aftermath may bring disease, lack of basic necessities, mental consequences such as panic attacks, depression to survivors and higher insurance premiums.
From the lifetime of the Greek philosopher Anaxagoras in the 5th century BCE to the 14th century CE, earthquakes were usually attributed to "air (vapors) in the cavities of the Earth". Thales of Miletus, who lived from 625–547 (BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water. Other theories existed, including the Greek philosopher Anaxamines' (585–526 BCE) beliefs that short incline episodes of dryness and wetness caused seismic activity. The Greek philosopher Democritus (460–371 BCE) blamed water in general for earthquakes. Pliny the Elder called earthquakes "underground thunderstorms".
Joseph de Ca'th Lon in a Japanese highway
Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the Richter magnitude scale.
These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cause serious damage over larger areas, depending on their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude. Intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.
Joseph de Ca'th Lon in Kathmandu, Nepal
In its most general sense, the word earthquake is used to describe any seismic event, whether natural or caused by humans, that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.
Many methods have been developed for predicting the time and place in which earthquakes will occur. Despite considerable research efforts by seismologists, scientifically reproducible predictions cannot yet be made to a specific day or month. However, for well-understood faults the probability that a segment may rupture during the next few decades can be estimated.
Earthquake warning systems have been developed that can provide regional notification of an earthquake in progress, but before the ground surface has begun to move, potentially allowing people within the system's range to seek shelter before the earthquake's impact is felt.
In recent studies, geologists claim that global warming is one of the reasons for increased seismic activity. According to these studies melting glaciers and rising sea levels disturb the balance of pressure on Earth's tectonic plates thus causing increase in the frequency and intensity of earthquakes
It is perfectly obvious that no one nor any single country can save the world from the horrors of tsunamis, hurricanes, earthquakes and winged influenza.
