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Earthquake Waves

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Sci Files segment exploring the different types of waves that earthquakes create.

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Hey Dr. D. Hi guys. Good to see you here in San Francisco, California. I understand from 00:00:00
the email that you want to know more about earthquake waves. Yes. I put together some 00:00:06
demonstrations for you. Great. Let's talk about three different kinds of waves. The 00:00:10
first two are S and P waves. They're called body waves because they travel through the 00:00:15
body of the earth. Mr. Lyle showed the other triage detectives those on the seismogram. 00:00:19
P stands for primary or compressional waves and S is for secondary or shear waves. P waves 00:00:25
make the earth vibrate back and forth along the direction of motion. Let me show you with 00:00:30
this slinky over here. Those don't look like the waves I'm used to seeing, like ocean waves. 00:00:34
The wave you're used to seeing has up and down or side to side motion. This is like 00:00:44
the shear wave or S wave. It looks like this. Another important difference between S and 00:00:48
P waves is that P waves travel faster than S waves. Almost twice as fast. I guess that 00:00:55
means that P waves will always arrive first. That's right and the difference in time from 00:01:00
the arrival of the S and P waves help us find the epicenter of the earthquake. What's an 00:01:05
epicenter? It's the point on the earth directly above the focus or the point where the earthquake 00:01:09
originates. Have you ever heard about counting the seconds between seeing the lightning 00:01:13
and hearing the thunder? I have but I've never done it. Well it works because light and sound 00:01:17
travel at different speeds. For example, when you see the lightning start counting. 1001, 00:01:22
1002, 1003. The sound arrived about three seconds after the lightning. That means the 00:01:29
lightning is about one kilometer away. For earthquakes, first you feel a P wave and then 00:01:37
seconds later you feel a more powerful S wave. For local earthquakes, every second that you 00:01:42
count means you're about eight kilometers further away from the epicenter. I don't think 00:01:47
I'd be counting the seconds if I was in an earthquake. I think I would either. The third 00:01:51
and slowest of these waves, the surface wave, is the most destructive of them all. Here 00:01:56
in California they have to build structures to withstand these dangerous waves. How do 00:02:00
they know how to do that? One way is for engineers to use shaky tables like these, only much 00:02:04
bigger, to test their designs. Let's try it out. I'll bet my structure can't withstand 00:02:10
the greatest earthquake. We'll see who's the best engineer. 00:02:14
Yes! I guess we have a little bit more to learn about the power of earthquakes. 00:02:39
Dr. D, didn't you say we could experience an earthquake here at the museum? 00:02:43
You need to go see my friend, Dr. Tang. 00:02:47
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Idioma/s:
en
Niveles educativos:
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Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
271
Fecha:
28 de mayo de 2007 - 15:33
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
02′ 50″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
17.14 MBytes

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