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Earthquakes: A guide to beginners (Manuela Villani)

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Subido el 14 de noviembre de 2015 por Francisco J. M.

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Lecture on seismology by Manuela Villani via Skype

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Okay, very good. So, good morning everybody, my name is Manuela, I'm a seismology, nanorobot, and enterprise company in London, and Alicia asked me to give you a presentation about earthquakes. 00:00:00
I hope I will say something useful for you, or maybe you know already everything. Just ask anything you want during or after the presentation. 00:00:15
Here I show you an image, this is a namazu, this fish is namazu, and the Japanese believed that it was this fish that caused the earthquakes. 00:00:28
Now of course we know that it's not like that, but this is a very nice picture. 00:00:42
In this talk, I will go through basic concepts about the pentatonics, hypo-effects, how we measure the earthquakes, and the effects of the earthquake. 00:00:47
And finally, I will talk a bit about what is the seismic risk and how we can reduce the seismic risk. 00:01:03
We all know here you have an example from the 1994 earthquake in California, Los Angeles. 00:01:10
But also sometimes cities can fall down. 00:01:24
This is a photo from the 1906 San Francisco earthquake in California with magnitude 7.8. 00:01:30
and you can see that the city was completely destroyed after the earthquake and the fire 00:01:38
that was caused by the earthquake. So where do the earthquakes occur? If we look at the 00:01:44
world map, we put on the map the epicenters of the earthquakes, so the location of the 00:01:53
earthquakes. You can see these dots, they are all epicenters and you can see that they 00:01:59
But they don't occur everywhere in the world, they have just very concentrated locations. 00:02:07
You can see in the oceans they follow this line and on the continents they are more spread. 00:02:15
It's not so clear, but also they follow some mountains as you can see here from the topography of the continents. 00:02:23
So the basic theory is the theory of plate electronics. 00:02:33
We have to say that the earthquakes occur along the boundaries of these plates. 00:02:39
You see we are here in Spain. This is the Euro-Asian plate. 00:02:46
It is moved, pushed in this direction toward northeast by the African plate. 00:02:52
This caused all those earthquakes in Italy, in Greece, in Turkey, in Hungary. 00:02:59
How did the earthquakes occur? 00:03:07
The basic theory is the elastic rebound theory. 00:03:12
If we have a fault that is perpendicular to this fence, 00:03:16
here you cannot see very well, but here there is a fault, 00:03:20
And there is some deformation beneath the surface of this land and this deformation will cause this side of the fault to go to one direction and this side to go to the other direction. 00:03:25
And eventually this will cause a breaking in the fault, the fault ruptures and we have the earthquake here. 00:03:41
And the earthquake will radiate certain waves. 00:03:50
The main waves are two types. 00:03:56
Primary waves are these waves that are in post-combustion and expansion. 00:04:00
And then we have secondary waves. 00:04:09
These are called primary because they are the first that are released during the earthquake. 00:04:11
So there are three waves. 00:04:17
And these are secondary waves, because they come later. 00:04:19
But after the E-wave and the S-waves, 00:04:25
we can have also some surface waves. 00:04:28
These will travel along the surface of the Earth, 00:04:31
while E-wave and S-waves will travel along all the body 00:04:35
of the Earth. 00:04:40
And you can just reference E-wave and S-waves 00:04:40
on the other side of the Earth. 00:04:44
The surface arrays are a very novel effect, but they are very, very destructive. 00:04:47
We have three types of folds. We have first fold. You can see here is the fold. 00:04:56
This side of the fold will go upward in this direction and will compress the other side of the fold. 00:05:04
This is a compressional fault. 00:05:13
We can have also this kind of a fault that goes below, that goes downward. 00:05:17
And in this case, we can have an extension. 00:05:23
But we can have also some side of the fault that moves just horizontally, not vertically. 00:05:27
In this case, one side of the fault goes in this direction, and the other side goes in this direction. 00:05:33
direction and this is a strike point. Here you can see an example of a truss fault. This 00:05:40
is the 1999 Qixi earthquake in Taiwan. The fault is, the trace of the fault is along 00:05:49
this line and you can see this is a truss fault because this side of the fault just 00:05:58
upward, it compresses the other side of the fold. 00:06:05
This is an example of normal fold. 00:06:12
So in the normal fold we said that one side pushed far away from the other, 00:06:16
and in this case you see that the space just was extended and it braked. 00:06:23
And this is an example of slightly fault. In this case, the fault is here, along this line. 00:06:32
This side of the fault moved in this direction, rightward. This side moved in this direction. 00:06:41
And you see the final effect is that the slit was completely shifted. 00:06:49
How do we measure our weight? So, this is a very old instrument to measure our weight, but it was invented by the Chinese. 00:06:54
You can see here you have, you have dragons, and here you have thoughts. 00:07:11
The dragons have a ball in their mouth, when an earthquake occurs, so the ball will fall, the dragon with the ball opposite to the center, just drop the ball that fall down in the mouth of the tot. 00:07:21
So when an earthquake occurs, the Chinese could go and see where the board was in the tors and understand where the earthquake was located. 00:07:39
Of course, now we will have more than one instrument to measure the earthquakes. 00:07:54
One is the seismometer. This is an example of a seismometer. 00:08:00
It is made by a rigid basis here, connected with some paper, a body circle, and here we 00:08:06
have a heavy mass connected to a pen. 00:08:19
When earthquake occurs, this basis will move horizontally in this direction, so this will 00:08:23
will move, but the mass doesn't move, and so the pen will draw a line on this paper. 00:08:31
This line is called seismogram, and you can see here an example of seismogram. 00:08:41
In the seismogram, you will see very clearly the arrival of e-waves. 00:08:48
they arrive first and they are primary waves. And after the P waves, we can see the S waves 00:08:56
arrival. S waves are normally very strong. They cause the strongest amplitudes on the 00:09:04
seismograms. And after the P and S waves, we will have the arrival of the surface waves 00:09:12
that are those that go on the surface, on the shallower layer of the Earth. 00:09:20
We can measure the force of an earthquake, and we normally use two types of measurements. 00:09:33
We have magnitude and the macrosatemic intensity. 00:09:39
What is intensity? 00:09:44
It is very intuitive. When there is an earthquake, we are in a certain location and we can feel the earthquake. 00:09:46
This is the scale. So we can be very close to the earthquake and say, oh it was very, very devastating. 00:09:57
or can be far away and we can see the earthquake as very weak or we can not feel at all the earthquake. 00:10:10
So the intensity is a measure of the effects of the earthquake and how we feel the earthquake was. 00:10:23
while the magnitude is a measure of the energy of the earthquake, not of the shaking that we feel. 00:10:32
The first person that proposed the magnitude was Richter in the late 30s. 00:10:44
He developed a method to describe the size of the earthquakes, but this method was a relative method. 00:10:53
He defined an aspect called the earthquake zero, and the magnitude Richter is a measure of the energy of the earthquake compared to the earthquake zero. 00:11:01
It's not a real measure of the energy of the earthquake. 00:11:16
What really measures the earthquake is the moment magnitude. 00:11:21
The moment magnitude is a measure of the energy released during this year's peak. 00:11:26
We have different scales of magnitude. 00:11:34
Richter's magnitude is called mL, and stands for local magnitude. 00:11:39
And you can see that if you have a moment magnitude A, for example, 00:11:48
and you go here local magnitude will be 6.8 because this magnitude scale just 00:11:53
saturates at certain point it's not very good after magnitude 7. so what we should refer to 00:12:01
is the moment magnitude but they know that the newspapers and everywhere you will see a greater 00:12:09
magnitude and when we can relate one another. But what means magnitude? When we change the magnitude 00:12:16
from one unit magnitude it means that the energy released was eight times the greater. So for 00:12:28
For example, if we have magnitude 5, the length of the fault will be around 0.8 kilometers. 00:12:39
But if we have magnitude 6, it would be already 5 kilometers. 00:12:48
And if we have magnitude 7, it will be 30 kilometers. 00:12:53
And in the magnitude 8, it will be 200 kilometers. 00:12:57
This is just to show that one moment doesn't mean very little change, it's a great, very large effect. 00:13:02
So in an aspect of curves, we have a hypocenter and we have seismic waves that radiate everywhere. 00:13:16
Closer to the epicenter, stronger the effect that we can feel. 00:13:26
So the effects of the earthquake will depend on magnitude, on distance, but also on the soil conditions. 00:13:32
If we are here, we are far from the earthquake, but if this soil is very very soft, for example it's sand, 00:13:43
The ground motion caused by the earthquake will be amplified a lot and the effect of the earthquakes on the buildings will be very strong. 00:13:53
So what are the effects of the earthquake? The first direct effect is just the ground shaking, so the motion of the earth. 00:14:05
And this is the primary cause of damage to buildings. 00:14:17
And here is an example. This is Northridge in California. The building completely collapsed during the earthquake caused by this strong shaking. 00:14:23
And also here is again California's Loma Prieta in 1989. This was a bridge with two decks and the upper deck, as you can see, completely fell down. 00:14:36
A secondary effect of the earthquake is the surface cold. Sometimes the cold is so shallow that it ruptures the surface. 00:14:49
You can see here an example where this was the fault of the earthquake and the space completely broke. 00:15:03
And this is another example, you have here a railway, and this side will default to our right, this side to our left, and you see that the rail was completely defromated by the earthquake. 00:15:15
Another effect of the earthquake is the tsunami. When we have an earthquake, of course, in the ocean, there will be a wave that is generated by the rupture with Freud. 00:15:31
And this wave is very, very destructive and can travel very far away from the center of the earthquake and many times destroy every single land. 00:15:47
Here, we have the example from the Tohoku Japan earthquake in 2011, and you can remember that most of the damage was caused by the tsunami, also the damage to the nuclear power plant in Fukushima. 00:16:00
Another effect of the earthquake are the land slides. 00:16:22
Here you see an example from Niigata in Japan in 2004. This house was on the top of the hill, but the hill just slide and the house fell down. 00:16:26
And another effect of the earthquake is liquefaction. What is liquefaction? 00:16:43
Sometimes when an earthquake occurs, what happens is that the soil liquefies. 00:16:49
It means that the soil becomes a liquid, so the buildings don't have anymore a basis where they can stand, and they just tilt. 00:17:00
If you see this example from Turkey, you can see that this building doesn't have any structural damage. 00:17:10
It just fell down because of the liquefaction of the soil. 00:17:21
This is another example from Ligada earthquake in Java in 1964. 00:17:26
So the questions that everybody asks, can we predict death phase? No, we cannot. We are not able nowadays to predict death phase. 00:17:32
But we can and we must reduce the risk. How? We should know first what is the hazard. 00:17:47
Hazard can be translated as peligrosidad, and in scientific terms, it's a probability that a certain level of grab motion will get exceeded in a timeframe. 00:17:56
What this means? That means that, for example, we can compute the probability of the direct effect of the earthquake. 00:18:09
So this is natural, and we cannot reduce the hazard. 00:18:21
This is the natural phenomenon, that is the earthquake. 00:18:25
But we can reduce the vulnerability and exposure. 00:18:29
The vulnerability is the tendency of the buildings to be damaged during an earthquake. 00:18:33
And the exposure is how many buildings we have. 00:18:39
So the combination of the hazard with the vulnerability and with the exposure will give us the risk. 00:18:43
So the probability that we will have a certain damage to the environment and we can reduce the risk. 00:18:51
This is the seismic hazard map for Europe developed by an international project called SHARE. 00:19:01
Here you can see where in Europe we have the higher seismicity. 00:19:10
Istanbul is a zone with very high seismicity. You can see that Madrid is a zone of low seismicity, if you're safe. 00:19:17
But the exposure is very important. If an earthquake occurs in this environment here, there are no buildings, very few people live. 00:19:27
We will have very low risk. If land space occurs in a city, in a very populated city as this one, the effect of the earthquakes will be very, very strong. 00:19:44
And the other contribution is the vulnerability of the buildings. Here you have three types of buildings. There are many more, I just want to show you the slides. 00:19:59
These are reinforced concrete buildings, so they are stronger. These are un-reinforced 00:20:13
masonry. Normally, our house is of this type. At Medici, if you live in a flat, it can be 00:20:21
of reinforced concrete. And here you have timber. Timber is just wooden buildings. This 00:20:29
this is an example. Normally buildings are designed to withstand the gravity force, so 00:20:37
they will resist to vertical forces. But earthquakes shake a building horizontally. So the problem 00:20:43
is that the buildings are not many times designed to resist horizontal forces. So what we can 00:20:54
do in the future is build something that is seismic resistant, in particular in an area 00:21:00
where we have high seismicity. And we have to design the buildings very well. In this 00:21:08
case, I want to show you a soft story building. Soft story means that it is a building where 00:21:16
there is a story that is very soft. Here is an example. You cannot see anymore, but 00:21:22
Below this there was another story that just collapsed after the earthquake. 00:21:30
You can see here the bars and columns just broke during the earthquake. 00:21:37
And here is another example. In this case the soft story was in the middle of the building 00:21:45
and it was less rigid than the other stories and during the earthquake 00:21:51
This building just, this story just collapsed, causing great damage to the air stability itself. 00:21:57
So we have to build the building in a way that the air resists seismic forces. 00:22:07
How we build air? We normally want the building to remain operational, frequent earthquakes. 00:22:16
This means that the building doesn't have any damage during a frequent earthquake that can be a low magnitude earthquake. 00:22:26
In occasional earthquakes the building should be built in such a way that it can be immediately occupied after the earthquake. 00:22:35
So people go away from the building but after the earthquake they should be able to go inside again. 00:22:45
In rare earthquakes, the buildings should be designed in such a way that we guarantee light safety. 00:22:54
So maybe the buildings cannot be reoccupied after the earthquakes, but people are not killed during the earthquake. 00:23:03
And for very rare earthquakes, so very large magnitude earthquakes, we should guarantee collapse prevention. 00:23:11
and so the building should not collapse in any case. 00:23:20
How can we prepare to face an earthquake? 00:23:30
In particular, when we live in a zone of high seismicity 00:23:34
like California, you can prepare before, during, 00:23:39
and after the earthquake. 00:23:43
There is on the California website 00:23:45
seven-step guide, for which they say that in step one, before the earthquake, you should 00:23:49
secure your space. So, for example, at home, you should secure the shelves, the walls, 00:23:58
you should move all the heavy objects, both up and down the shelves, in order to not fall 00:24:05
We should do a plan to be safe, so just sit down with the family and say, okay, if an 00:24:13
earthquake occurs, we should go away from the house and meet in a certain place altogether 00:24:23
if we cannot communicate. 00:24:31
We should organize a kit. 00:24:33
In a box, we should put some cans with food, some money, money but not, for example, 100 euros, but small tickets like 20 euros. 00:24:36
And we should minimize the risk of our house. 00:24:53
And during the earthquake, what we should do? 00:24:58
We should go on our knees and cover our head and go behind and below a desk, for example. 00:25:00
Please drop, cover and hold on during the shake. 00:25:08
And after the earthquakes, we should just follow our plan to go where we decide to go 00:25:14
to improve the safety and just see if somebody was injured during the earthquakes and then 00:25:20
reconnect with our relatives. 00:25:25
So this can seem very extreme, but I actually meet many families in California, but they have this, they have a kit with something, with cats, with tuna, or other food, with money, with crosses, and emergency kit, and so on. 00:25:27
Because if you live in a country where earthquakes can occur and will occur, you should prepare for that. 00:25:49
So this is the main point during the incubate, just drop, cover and hold on after the shaking will pass. 00:25:57
And this is the end of my presentation. Thank you. 00:26:07
Okay, don't you have any questions? 00:26:46
None of you? 00:26:51
No. 00:26:54
No worries. 00:26:55
Okay. 00:26:56
Manuela, . 00:26:57
Thank you for your conference. 00:27:23
Hola. 00:27:25
How are you? 00:27:27
I'm very well. 00:27:28
In Spanish? 00:27:29
Yes. 00:27:32
I wanted to ask you how you became a seismologist. 00:27:33
What did you do? What did you study? 00:27:37
Where are you now? 00:27:40
Can you tell us a little bit about you? 00:27:41
Because we have heard you and what Alicia has told us. 00:27:42
But well, so that we know a little bit about who you are, what you do. 00:27:45
I am from the south of Italy, I studied in Milan, in the Polytechnic of Milan, and one of my subjects was Engineering Seismology, so Seismology applied to Engineering, and I liked it a lot. 00:27:49
So I did a doctorate in seismology after the degree and I worked in research for a while, I worked in California, I worked in Italy and now I work in a company here in London. 00:28:09
and what I normally do is what is here, seismic hazard. 00:28:26
I mean, when someone wants to build an electric plant all over the world, 00:28:34
not in the United Kingdom, which is not very seismic. 00:28:44
So, the first thing you have to do, also in an area that is not very seismic, is a study of seismic peligrosity. 00:28:50
So, what I have to do is study the faults that there are in a certain area, the maximum magnitude that there can be, 00:28:59
y al final lo que tengo es algo como parecido a esto. 00:29:14
Por un símbolo, una ciudad o un sitio, calculo la peligrosidad sísmica, esto es lo que hago. 00:29:19
Luego normalmente los ingenieros estructuristas lo que hacen es construir los edificios 00:29:27
teniendo en cuenta este nivel de peligrosidad. 00:29:34
Eso es todo. 00:29:41
Thank you. 00:29:44
Idioma/s:
en
Materias:
Biología, Geología, Ciencias
Autor/es:
Manuela Villani
Subido por:
Francisco J. M.
Licencia:
Reconocimiento - Compartir igual
Visualizaciones:
89
Fecha:
14 de noviembre de 2015 - 11:32
Visibilidad:
Público
Centro:
IES ALPAJÉS
Duración:
29′ 45″
Relación de aspecto:
1.78:1
Resolución:
854x480 píxeles
Tamaño:
213.56 MBytes

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