What would happen if a strong earthquake occurred around some of Iran’s underground Nuclear sites? Would they be destroyed?
Since they were built with enemy bombardment in mind, my guess is that they’re pretty well hardened and secured. Obviously, if the earthquake is BIG enough, then nothing is safe.
This site notes that, in France, nuclear power plants are designed to withstand a quake that is twice as strong as the calculated/expected “1000 year event” quake. The Iranians may or may not have built to those standards. And, of course, events in Japan are also instructive…and maybe a bit worrying.
There was an earthquake in 1980 which destroyed 6000 plus centrifuges in Pakistan. A fact which was only revealed in 2010.
From this source, it was a 7.6 Richter quake, pretty damn hefty. Says it killed over 73,000 people. I don’t know if this qualifies as a “1,000 year event” or not. (Hope so!) So, yeah, if the quake is big enough, it can destroy damn near anything.
That was in 2005. The 1980 one was relatively minor, did not even damage the building, but it destroyed the centrifuges.
Also, caves and underground structures are pretty safe in earthquakes. The surface motion is what causes damage during earthquakes and if you’re not at the surface, there’s no motion. There might be damage to support structures there are at the surface, but the stuff inside the underground bunkers (or whathaveyou) would be fine. Depending on how deep these things are, the people working there might not even feel the earthquake-- people who have ridden out strong earthquakes in caves have reported only a rumbling noise, but no actual motion.
Really? That’s exactly the opposite what I would’ve thought.
Not an expert, but I gotta dispute this. I think that natural caves can be surprisingly strong and may in cases be safer than you would expect. However there is always a danger of rockfall and even little stuff can kill. I don’t think I would want to be underground.
Earthquake mechanism involves localised slipping on a fault plane. The centre of the slip zone is the focus and may be close to the surface but can be many km deep. Example. Shock waves of various kinds propagate in all directions (vertically as well as horizontally). Structures (natural and man made) fail by a variety of mechanisms but principally by the ground acceleration experienced causing weakening and detachment of structural components. This acceleration is not just experienced at the surface but in all rock material that the seismic waves pass through.
Centrifuges and assorted machines are sensitive equipment. An earthquake does not need to destroy the structure, the shaking can damage the equipment on its own.
I think you might be a little confused here. Movement along a fault plane is what releases the energy in an earthquake, but that doesn’t mean there’s a whole coherent block of crust moving from however many kilometers deep all the way up to surface.
Nope. With earthquakes, the P and S waves are what send the energy from the hypocenter to the surface, but these waves merely propagate through the solid material without actually causing any acceleration until they arrive at the surface. Imagine one of those executive stress relievers with the dangling balls, where you whack one end and the ball on the other end moves. Being in a cave would be like being inside one of the center balls-- the energy is transferred through the material around you but you don’t actually feel any acceleration as a result.
Now, granted, most tour-able caves (and presumably nuclear bunkers) are near the surface, so sometimes they’re near enough to be affected by surface vibration. The entrances are also usually vulnerable. With underground structures, there can also be risk if they’re dug into soft sediment, but a Cheyenne Mountain style bunker blasted right into the bedrock should be fine.
(Incidentally, this is why you can get limestone caves with fairly delicate speleothems in very seismically active areas.)
How large of a void within solid material (like a cave) do you need before the P and S waves treat the void like “the surface” and start causing accelerations? Does it need to be some significant fraction of the wavelength? And do any reasonable caverns approach that size?
Iran has lots of quakes, and nasty ones, to boot.
I suspect they’ve planned for them.
I didn’t say that. I did say that the slip zone is the origin of seismic waves. The waves are a propagation of energy. There is acceleration of rock material as the waves propagate. That’s what the wave is.
This doesn’t make sense. The seismic wave is movement – vibration – not a whole lot different in concept from a sound wave. Alternating movement means there is acceleration. We are not just talking about force transfer here.
Are you suggesting that the P waves and S waves convert to surface waves once they reach the surface? I have a couple of comments.
- Note that I am not an expert. Just a school teacher. And I have lived most of my life in a geologically active country. And I have been reading, researching and following the Christchurch quakes closely for a couple of years. This is the first I have heard of this.
- P waves, S waves and surface waves propagate at different speeds. Surface waves reach seismometers some time after the P and S waves. This seems contradictory to what you are saying.
- If there is such a conversion, then surely it would occur at any surface where the P waves and S waves reached open space or a void. Therefore being in a cave would not be any different from being on the surface. If I locked myself in a safe that was bolted to the bedrock I am sure that I would feel some shaking. Even if said safe was in a mine several km underground.
Fine if it was just transmission of force. However we are talking vibration here. Jiggle that end ball and you will get movement all the way down the line at any point where the structure allows relative movement between the components.
I suppose I phrased that poorly. Yes, there is acceleration as P waves pass through rock, but it’s small-scale acceleration of particles within the rock, not actual coherent chunks of rock moving. It is indeed much more comparable to sound waves than the destructive shaking that causes damage at the surface. And yes, people who have been in caves during earthquakes have felt shaking, but mostly in their eardrums!
That’s exactly right.Cite:
It’s odd that most of the pages describing seismic waves don’t explicitly say that, but since surface waves can only travel along the surface, how else would they get there?
Although, keep in mind that if you have something like the San Andreas fault where there’s actual fault movement at the surface, surface waves may be generated right there. With deep earthquakes, though, surface waves are only formed when P and S waves reach the surface.
Surface waves do travel slower, but they’re also taking an indirect route. The P and S waves travel directly to the seismometer from the hypocenter, but the surface waves don’t exist until the P waves arrive at the surface. After that, they propagate out (most intensely) from the epicenter along the surface. If you had a seismometer right on epicenter, the first P waves and the surface waves would indeed appear to arrive at the same time.
Okay, so admittedly I’m a little shaky on this point (:D), but somehow with cave-sized voids the P and S waves are able to simply deflect around instead of getting trapped and having to convert into surface waves.
Background: IAAGeologist, but not one that regularly deals with seismology. I did take an intro geophysics class where the “earthquakes in a cave” topic came up tangentially, though. I actually did a little bit of research with the journals I had access to at the time and my impression was that the fact that earthquakes are heard but not felt in caves was fairly well-established but not particularly well understood. But I suppose that’s veering dangerously close to “my post is my cite” territory.
Here’s one of the few publicly-available pages I could find that deals with the topic when it came up here a couple of years ago, although a National Park newsletter isn’t exactly an authoritative text. Oh, also (PDF): http://www.nps.gov/wica/naturescience/upload/RM%20Ramblings%20Fall%2008%20v.%206%20n.%208.pdf