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It's certainly interesting how the coastlines are so immune period down to where it narrows big-time, but how vulnerable inner parts of the provinces surrounding Rome, Naples and Bari actually are...
Role reversal complete when compared to how it is in California for example!
I know that this post is some months old, but I want to try to give some explanation about this. The different distribution of high seismicity areas in the two cases is mostly related to different kinds of tectonic movements and kind of seismic faults.
- California has some huge seismic faults, the most famous being the San Andreas fault. This fault is characterized by a horizontal movement of the two land masses on the two sides of the fault, that move parallel to the fault trace. https://en.wikipedia.org/wiki/San_An...Sanandreas.jpg
I don't know in detail the distribution of all the seismic faults of California, but I'm quite sure that the driving force that formed a lot of them can be ascribed to this antiparallel movement of the North American plate and the Pacific plate.
- The Italian fault system is formed by a completely different kind of movement: it is caused by the African plate moving toward Europe. This movement tends to form seismic faults in which one land mass slips above the other: https://www.google.it/search?q=fagli...GpSYQLbPCwB_M:
This phenomenon also caused the formation of the Apennines mountain range, over a really long time span of course.
So, in practice the most of seismic areas in Italy are mountainous areas because the seismic activity itself formed those mountains. Also, earthquakes are continuing to go on in those areas because those mountains are still forming and changing.
*Borders of the tectonic plates over the Mediterranean sea (yes, they are pretty complicated) https://www.google.it/search?q=fagli...VvupZSMOM92vM:
*Main seismic faults in Italy: http://www.focus.it/site_stored/imgs...-2.630x360.jpg
By the way, what is the earthquake preparedness in urban zones like Reggio Calabria, Messina and Catania these days? Are those isolated urban areas getting as well-drilled as San Francisco/Tokyo or are they just as vulnerable as L'Aquila and those areas around there?
I guess lessons there better have been learned from 1908...
By the way, what is the earthquake preparedness in urban zones like Reggio Calabria, Messina and Catania these days? Are those isolated urban areas getting as well-drilled as San Francisco/Tokyo or are they just as vulnerable as L'Aquila and those areas around there?
I guess lessons there better have been learned from 1908...
About this, we don't demonstrate to be much prudent, and the overall situation is quite shameful. We have a new strong and destructive earthquake every few years (the last ones being in 2009 in L'Aquila, the sequence in 2012 in Emilia and the sequence that started last August in the central part of the Apennines), and every single time everyone says "we should build only anti-seismic structures, we know that our country is really prone to earthquakes!". Even so, after 6 months from the end of the seismic sequence everyone seems to forget about prevention (or, more likely, a lot of people prefers to ignore the problem. Sadly, in Italy we are ignoring too many problems already...).
From what I have seen, the areas in which there are more anti-seismic buildings are the ones that have been reconstructed after a large earthquake in the after WWII period (so when the people started to take seriously anti-seismic buildings). So, right now, L'Aquila is probably more anti-seismic than Reggio Calabria and Messina.
This article has some numbers about this topic: In Italia le nuove case antisismiche sono il 27%
The first information given in this article is that only the 27% of new buildings are anti-seismic (considering all the country). It also shows the percentages region by region: it is immediately evident how regions who had some strong earthquake in the last decades have the largest percentages (Abruzzo with 39%, Friuli Venezia Giulia with 38%, Umbria with 37%, Calabria with 33%....), while the last one is Sardinia (which is practically considered a not-seismic area). Strangely, Sicily is the second last with only the 13% of new buildings made following the anti-seismic rules. This is only about new building, so overall the percentage is probably shamefully low.
According to our national laws, new buildings should be build according to the seismic risk of that area: the more likely a strong earthquake is, the most anti-seismic buildings should be. The laws are even stricter for public structures (such as schools and hospitals), that should always be completely anti-seismic.
This is the theory, but the practice is all another thing.
Sadly, about housing we have a huge issue which is called "abusive house building". With "abuse house building" I mean that a lot of people build new houses without any authorization, without paying any tax, and often in places in which it is completely forbidden to build because it is too dangerous (seismic risk, volcanoes risk, more likely hydro geological risk).
Abusive building can also indicate unreported modifications of an existent building, which sometimes can cause structural problems too.
The most classical example are the houses build on the side of the Vesuvius
As an example, even the hotel that was destroyed by an avalanche caused by the last strong earthquakes in January was abusive. So it makes 30 deaths that could have been avoided. (I'm talking about this --> https://www.theguardian.com/world/20...valanche-hotel )
Even public buildings have huge issues, which in this case are called corruption, mafia infiltration into the project and so on. In practice, it can happen that the company that gets the contract doesn't follow the original project and switch to cheaper materials just for increasing their profits. They just want to get the money, they don't care at all about rules and our safety.
This problem is really widespread, and it's a huge problem both for economy and for our safety.
The most common situation I have heard of is the substitution of construction sand (taken from rivers and other inland places) with seaside sand. The second is much less expensive, but it is also full of salt. This favors the deterioration of the steel used in reinforced concrete, making the whole construction much less durable that how it was supposed to be.
Apart this, a lot of public buildings and infrastructure are not anti-seismic just because they are too old.
Just for making a couple of examples, during the L'Aquila earthquake a building for university students was destroyed, killing 8 students. That one was an old building, that underwent several modification that compromised its structural stability. Albeit this, it has passed an antistismic control just one week before the famous earthquake, and it was labeled as safe. The responsibles for the safety of that building have been definitively condemned to a couple of years of jail just last summer (7 years after the disaster).
Another example, the elementary school in San Giuliano di Puglia, that was destroyed by an earthquake in 2002, killing 26 children and one teacher https://en.wikipedia.org/wiki/2002_Molise_earthquake
Even in this case, tribunal condemned the constructors of that school for this disaster. In this case, they added one floor to the school without paying too much attention to the stability of the building.
In practice, I would sadly conclude saying that we are considering even the earthquake issue in a really Italian way...
Thanks for letting me know, in other words something like 20 k people could easily die again if a 8.0 struck the Messina strait?
That is just madness.
Even here houses are very strong. The roofs have to be able to cope with strong storms occasionally and basically no roof fell in on itself during the 2005 winter storm. Therefore I think houses in this non-seismic area should be able to cope very well if a very freak (1 per million years) quake would happen. I think it's a general issue that Italy needs to develop building standards as seen in the rest of the western world, even that would be a major step from the shambles its poorer area's buildings are in.
Thanks for letting me know, in other words something like 20 k people could easily die again if a 8.0 struck the Messina strait?
That is just madness.
Even here houses are very strong. The roofs have to be able to cope with strong storms occasionally and basically no roof fell in on itself during the 2005 winter storm. Therefore I think houses in this non-seismic area should be able to cope very well if a very freak (1 per million years) quake would happen. I think it's a general issue that Italy needs to develop building standards as seen in the rest of the western world, even that would be a major step from the shambles its poorer area's buildings are in.
Your area looks faily safe though Urania?
If an earthquake with a magnitude of 8.0 struck on any densely inhabited area of Italy the number of victims would be huge. As you pointed out, a lot of the most seismic areas of Italy are mountainous places, with a relatively low population density. But several important cities are in areas with the highest seismic risk, such as Campobasso (49 241 inhabitants), Potenza (67 211 inhabitants), Benevento (60 102), Terni (111 376), Isernia (21 850), Cosenza (67 538), Catanzaro (90 435), Catania (313 540), Siracusa (122 049 )... and of course Messina (237 603) and Reggio Calabria (182 596).
The northern half of the country is generally less seismic (apart the really north-east part), but it has a much higher population density. So even a weaker earthquake on those areas could cause large damages.
Just to read the number of people who live in an area with a really high seismic risk is really scary for me.
The earthquake that hit Messina and Reggio Calabria in 1908 was the worst in our records, and the recorded magnitude was "just" 7.1. The earthquake was followed by a tsunami, that together destroyed both the cities and killed 120 000 people (estimated).
In the last 50 years, the earthquake that caused the most victims is the one in Irpinia (https://en.wikipedia.org/wiki/1980_Irpinia_earthquake). The magnitude was "just" 6.9, but it killed nearly 3000 people, injured 8800 and left homeless 280 000 (other than victims, also the number of people who remain homeless is really important).
Looking at our actual situation, even if really sadly I have to conclude that the worst scenario* I can think of would not have a much different development than those examples.
(*Worst scenario I can think of = earthquake with an high magnitude, with a long-lasting shake, that hit over an highly populated area without any previous weak shake that makes the people evacuate the building before the strong one*).
About our building, traditional housing consists in bricks, concrete and (more recently) reinforced concrete. All those materials are really rigid, and don't behave well at all during an earthquake.
If I'm not wrong, Sweden traditional housing is much more into wood than us. So, ironically, Sweden not-antiseismic houses would probably behave better than our not-antiseismic houses during an earthquake (which is quite depressing...)
About my place, I live on the westernmost part of Italian Alps, which is classified as an seismic risk 3 area (there is a scale of 4 points, in which 1= really high seismic risk and 4= really low seismic risk). This means that my place is unlikely to get a strong and destructive earthquake, but this is not impossible.
Anyway, those estimations are not always completely reliable. For example North eastern Italy was not considered an highly seismic area before the earthquake that hit the region in 1976 https://en.wikipedia.org/wiki/1976_Friuli_earthquake
In Ischia superficial and destructive shakes, that volcano* is still active, says Gianluca Valensise (national institute of geophysics and volcanology) The seismologist says: "the episode that hit the island is completely different from the Central Italy ones. No effects on Vesuvius nor Campi Flegrei are predicted.
(*they are referring to the island of Ischia itself, which is actually a volcano too*)
We are in the hearth of a volcano which is still considered active, here in Ischia. Next to the Campi Flegrei, which are still rising and have been in warning conditions since 2012. Earthquake in this area have a completely different nature from the ones in central Italy, explains the Ingv seismologist and head of the research department Gianluca Valensise. "These are shallower shakes, thus more destructive but also really localised."
What's the mechanism of volcanic earthquakes?
"They don't generate because of plates movement. They are caused by the periodical collapsing of the volcano under its own weight. Last Ischia eruption dates back to the middle ages, so it is still considered fully active. At depths greater than 5 Km, rocks heat and melt, and thus earthquakes cannot generate at these depths. All the shakes registered in volcanic systems are thus generated at really low depths."
Why superficial earthquakes cause so much damage?
"Because the shakes happens near the surface, where houses are. On the other hand, the area covered by the phenomenon is really limited. The first measured indicated a depth of about 10 Km, but it was only a prefixed value, automatically broadcasted before it was possible to fix the real depth."
Volcanic earthquakes can cause never-ending earthquake swarms, like in central Italy?
"No, we expect some other shakes, but not really a year-lasting earthquake swarms like in central Italy (*the area in central Italy hit by last year earthquake is stil shaking quite often, but they didn't have any great shake for a while*
How often does Ischia have earthquakes?
"The greatest shake of the island history is the 1883 one. The Casamicciola (*town in Ischia*) earthquake nearly happened in the same area of today's one. Even that time the magnitude was relatively low, but it caused a huge number of fatalities. Among the ruins also Benedetto Croce's parents died. (*more about this earthquake in here ) Since then no other important shakes were reported. Therefore, on the island could be present a large number of old and run-down buildings.
Can this earthquake awake Vesuvius or the Campi Flegrei supervolcano?
"No, the three volcanoes of this area (Ischia, Vesuvius and Campi Flegrei) are considered as independent one from each other. We don't expect nothing like that."
Just had a 4.9, 23km SE of here. 90km deep, but still a bit of rattling.
Now a 5.0 and 74km deep.
Last edited by Joe90; 12-07-2017 at 01:49 AM..
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