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Thread: Himalayan Earthquakes

  1. #1 Himalayan Earthquakes 
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    This is just a shameless plea for people to share their knowledge/ references (web links would be good ) regarding Himalayan Earthquakes. I want to know how and where they are generated, I am particularly interested in the role that the Tibetan plateau has to play.

    So far I have it that India is being subducted beneath Tibet, the crust beneath Tibet seems to be unusually plastic and it is extending at right angles to the subduction. There is debate as to where the strain energy is released which causes earthquakes: people have assumed that the release of compressional strain accumulating close to the Greater Himalaya has been responsible for earthquakes, but now there is a group whi suggest that a 'significant fraction of the southernmost 500 km of the Tibetan plateau participates in driving great ruptures'.

    (Feldl & Bilham, Great Himalayan earthquakes and the Tibetan plateau, Nature, Nov 2006)


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  3. #2  
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    Usually subduction zones are paralleled by chains of volcanoes, I think you will find the indian plate and asian plate are merely pressing together and causing the mountains to rise. BUt you might want to check this. PLate tectonics came out way after I left school!


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  4. #3  
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    It is often said that continental crust cannot be subducted, however, according to my structural geology lecturer this is 'just something we tell first years'. I must admit I don't know much about the area, hence the need for a thread, and perhaps there are no volcanoes, although geophysical studies have found anomalously plastic material in the crust beneath Tibet so I guess it's quite possible that there is partial melting down there but it just hasn't been able to penetrate through the immensely thick crust.
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  5. #4  
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    It would have to come back up somewhere, it always does! you can't just have an ever increasing bubble gas/water vapor etc indefinitely building up.
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  6. #5  
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    Quote Originally Posted by Megabrain
    Usually subduction zones are paralleled by chains of volcanoes, I think you will find the indian plate and asian plate are merely pressing together and causing the mountains to rise. BUt you might want to check this. PLate tectonics came out way after I left school!
    I think that perhaps we can make a distinction and an exception of the Himalayan subduction zone because it is not a typical subduction zone. The most obvious distinction is that it is a continental collision zone, most subduction zones have ocean lithosphere colliding with continental lithosphere. There are a couple (that I can think of) major differences which might explain why you don't get backarc volcanism. First, the continental lithosphere is not going to be so enriched in hydrous volatiles, so the melting temperature is going to be too high for magma generation. Second, the actual dip of the subducting slab is going to be too shallow to promote back-arc extension, which helps relieve the pressure which lowers the melting point. That's why the Tibetan Plateau is so high.
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  7. #6  
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    I can't argue with you it's not my field, when i get some time I will have a look but I'm looking into GW at the moment...
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  8. #7  
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    The article in Nature that I reference in my OP is quite interesting. It basically says that Tibet soaks up lots of strain energy and kind of stores it. When there are earthquakes in the Greater Himalaya if the rupture lengths are less than about 150 km (which they typically are) then strain energy isn't drained from Tibet. After that strain energy can be released from Tibet which more than doubles the slip available to drive earthquakes along the frontal thrusts, these happen occasionally and are quite large events. However, every 1,000 yrs or so there is geological evidence that suggest there is a megaquake, where lots of strain energy from Southern Tibet is released. So perhaps there will be a really big one > Mw=9.2 (<--possibly?) in the Himalayas in the not-so-distant future.
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