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We just (20mn ago) suffered from another strong aftershock (of the initial March 11th earthquake) in Japan.

I have some questions related to seismic science.

  1. Why is there so much time between the initial quake and the following strong aftershocks (initial was March 11, the stronger aftershock happened 20mn ago, April 7)?

  2. Why does it seem that progress in seismic science (and quakes predictions) is so poor? It seems people have only raw probabilities, based on historical data.

  3. Would anybody have any graphical / imagery data of the physical fault move on March 11?

Thank you.

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Hi ring0. This is a quick language note - I assume you're not a native English speaker. With, "I expect knowledgeable answers," I know you mean to express confidence that the community can give you quality responses. Unfortunately, this usage is ambiguous in English, and could also mean that the speaker has an expectation and the reader is required to live up to it (think of a parent saying, "I expect your room to be clean before I get back.") This was the first interpretation that came to mind for me before I re-read the sentence. It's a minor point, but I thought it might be helpful. –  Mark Eichenlaub Apr 7 '11 at 15:14
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@Mark thanks, fixed the question to be less "authoritative"! –  ring0 Apr 7 '11 at 15:20
    
By the way, this is not really the place to ask about data recorded from the earthquake on March 11; that question would be better served on a geology or seismology site. (Actually, the same could be said of all your questions, but physics does have some bearing on the first two.) –  David Z Apr 7 '11 at 17:29
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As for your third question - Download Google Earth, if you haven't already. It has a layers section. Select "earthquakes" and zoom in near say Japan's coastline. Tons and tons of data lies there including satellite imagery and whatnot. Explore away. ps: For live earthquake data there is nothing better than the USGS earthquake.usgs.gov/earthquakes/recenteqsww/Maps/region/… –  user346 Apr 7 '11 at 17:52
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And go to this page for far more and better data on earthquakes, including ground movement maps. These are KML files which contain geographic data so you can open these in Google Earth (or other GIS). –  user346 Apr 7 '11 at 17:55
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2 Answers 2

up vote 1 down vote accepted

I also live in an earthquake prone region,in Greece, and we got a 6.3 a week or so ago, fortunately in the middle of the sea between Crete and Carpathos.

We got two stong ones in Athens during my life time: one in 1981 and one in 1990, from different fault lines, though all of them finally are due to the fact that the African plate is pushing against the European one. At the time of the shocks all physicists in my region read up on seismology. It is not an advanced science. Some tried to predict aftershocks with dubious results : large error for epicenter, large error on time, etc.

It is known that the pressure builds at the fault until it breaks. Then the system settles with "small" after shocks, going on for months. Large after shocks can also happen. Predictions are very uncertain.

This link may help.

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Thanks. An explanation about why there is so much time between large aftershocks would be appreciated. –  ring0 Apr 7 '11 at 15:45
    
@ring0 what follows is my opinion: It takes time for pressures to equalize after the main shock. Think of a pile of gravel with some sticks partly out from the bottom. Pull out one stick. The pile crumbles at that point. After a while, depending of how the other sticks got reoriented, an other avalanche can start. The time is random, roughly dependent on friction parameters, and weight distributions etc. In the real earth, the fault lines are km long, it takes time for the pressure to redistribute and upset a neighboring fault which became ripe, because of the main shock. The time is random. –  anna v Apr 7 '11 at 15:52
    
continued: some have tried to correlate tides with earthquakes. It is not clear. There are earth tides, the ground lifts about 40cms when the tidal bulge passes. It might trigger a balancing fault, so that might explain the month delay. No proof. Just handwaving. The large aftershocks in Greece happened a week after and then a month after too. Who knows ;). –  anna v Apr 7 '11 at 15:57
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Why does it seem that progress in seismic science (and quakes predictions) is so poor? It seems people have only raw probabilities, based on historical data.

It's because the actual earthquake depends on tiny initial events.

Imagine standing on a glass so it breaks. We can calculate how much force it takes for a glass to break. But it would be very hard to predict in advance at which microscopic atomic scale flaw in the material the crack will start and at exactly what nano-second.

An earthquake is just the same on a larger scale.

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"An earthquake is just the same on a larger scale." And in an inhomogeneous and not directly observable medium. –  Omega Centauri Apr 7 '11 at 18:15
    
Ok thanks. I got an explanation about why there is no progress... Now I'd dream to get an answer to the question number 1. –  ring0 Apr 9 '11 at 9:28
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