[martok2112]

My roomie is a little better versed on the how's and why's of why we've never seen this before with Japan, Saquist, but I do remember seeing as an additional report regarding this tragedy that earthquakes in the ocean do not always produce tsunamis. This was an eventuality, but not a certainty with each quake.

[kevin]

Originally Posted by Saquist

how come we've never seen this before with japanesse earthquakes...tsunamis and such? Was it just because this was in the water?

According to an interview with a seismologist that I saw on the day of the disaster in order to create a tsunami you have to have an earthquake of around 7.5 or more.

This is to create one that is a danger, you can get them with lesser quakes but they would be unlikely to be as devastating. For perspective, the 2004 Indonesian Tsunami was caused by a 9+ richter scale event. It's also important to remember that much of the scale of devastation on both these events was not caused by the quake - which Japan is pretty well prepared for - but by the size and scope of the Tsunami it created under the ocean.

Unfortunately, I think the death toll may rise much further than it currently sits. There are reports there are at least 10,000 people unaccounted for in just one town alone that has been obliterated by the wave.

[MagaditH]

Originally Posted by Saquist

how come we've never seen this before with japanesse earthquakes...tsunamis and such?
was it just because this was in the water?

The Quake came from the Marianas Trench which is a subduction zone that follows the coast of Japan and which is why Japan is subject to earth quakes quiet often and the quake has to be large to push that much water.

[Quark]

They did mention Santa Barbara and Santa Monica, the latter being where I live. And it's right on the Pacific.

[Akula2ssn]

Originally Posted by Saquist

how come we've never seen this before with japanesse earthquakes...tsunamis and such?
was it just because this was in the water?

There are numerous different types of earthquakes such as fault earthquakes of which there are 3 types of faults associated with them that can take place, and as far as I know, not all of them are associated with tsunamis. Nor does there need to be an earthquake to cause a tsunami. Landslides can cause them as well as explosions.

The simplest way to put it is that in order to create a tsunami you need a sudden displacement of a large body of water. The classic example is in the case of a megathrust earthquake. It's not the shaking of the earth that causes the tsunami but something much larger. In these megathrust earthquakes, entire sections of faultline on the order of thousands of kilometers can be displaced vertically on the order of 10s of meters. The Cascadia earthquake of 1700 is one such example and even today we still see evidence of it here in Washington state. During that earthquake, the length of the fault rupture is estimated to be around 1000m or 620mi and the displacement was about 20m or 22yds. It's not the rumbling that causes the tsunami, it's the sudden displacement of 620 miles of rock that causes it. Not all earthquakes cause that kind of displacement and if they do, not all of them cause a vertical displacement, in some cases its a horizontal displacement. Since the pacific Northwest of the US hadn't been settled yet in 1700 there are no immediate records of the quake. However, it's believed that the quake took place around 0900 on January 26, 1700. However, hours afterward, Japan was hit by a devastating tsunami. The source of that tsunami had remained a mystery until recent years when studies of tree rings from an entire forest of dead red cedars showed that the last growth rings in those trees were from 1699. This would have been the last growth before the earthquake. When I went out into the field as part of an ocean geology class for my major, we went to see some of those trees. To put it bluntly that quake lowered an entire coastal forest down into the intertidal zone and the seawater killed the forest.

So let's say I have a pool of water and there's a fault in the center that runs across the width of the pool. If I cause some horizontal displacement of the floor at the fault line where the pieces of floor (ignore the walls, we're keeping them stationary) on either side of the fault just slide horizontally, there's not much if any displacement of the water. So no wave is generated. However, if I were to suddenly drop one side of the fault, or raise one side there is going to be huge displacement of the water over the displaced floor. That will actually create a wave and a huge one. With the 2004 megathrust earthquake in the Indian Ocean, the fault length was 1600km or 994mi with a 40m vertical displacement. I haven't followed the news all that closely, but I suspect that this quake from yesterday is probably a megathrust quake.

[horatio]

I hope this won't be second Chernobyl and radioactivity "just" leaks out. That's already bad enough in a high population density country like Japan.

[Quark]

Yeah, and the effects of Chernobyl are still occurring to this day...

[kevin]

Originally Posted by horatio

I hope this won't be second Chernobyl and radioactivity "just" leaks out. That's already bad enough in a high population density country like Japan.

According the news I've been following it's not currently rated as being as severe an event as that. It's currently not even being rated as being as bad as Three Mile Island.

That's at least according to the people who do this kind of rating analysis.

[Akula2ssn]

I heard about the explosion at one of the plants last night, but I didn't pay much attention to the article. Everything I read was completely devoid of any factual information to draw any conclusions. It just said explosion, which means almost nothing for numerous reason. People tend to mistake things for explosions that aren't really explosions, and even if it was an explosion it's not necessarily associated with the reactor. From what I've been reading today, it's not even a meltdown which is what Chernobyl was, or a partial meltdown like Three Mile Island. The reactor and the structure it is contained in, is supposedly still intact.

Edit: the one thing I'm concerned about is how badly damaged is the cooling system.

[horatio]

Originally Posted by kevin

According the news I've been following it's not currently rated as being as severe an event as that. It's currently not even being rated as being as bad as Three Mile Island.

That's at least according to the people who do this kind of rating analysis.

The company tricked the public before, the regulators have only imperfect insight and more than 100.000 people are evacuated so it's safe to assume that a meltdown is happening. The chances that the thing explodes might be small but we all know Murphy's Law.
I am not anti-nuclear but with three nuclear worst case scenarios during the short time in which we have used nuclear energy I am not a technology apostle either.