Question: Is it possible than 2 earthquakes begin simultaneously?

Asked by hatsuneirina to Alice, Andi, Bas, Daniel, Rhian on 14 Mar 2015.

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  1. Photo: Bas van den BergBas van den Berg
    answered on 14 Mar 2015:

    Hi Hatsuneirina,

    I’m sure Andi can formulate a better answer to this question but I’ll give it a try anyway. Andi, please tell me if i got things wrong here!

    earthquakes happen generally at plate boundaries, and since there are many plates, there are many plate boundaries, many of them move quite independently from each other, so yes it is definitely possible that, by pure coincidence, 2 earthquakes happen at the same time in 2 different plate boundary zones that have nothing to do with each other. But i would say that the chances are very unlikely since there are not so many (big) earthquakes happening frequently anyway.

    As for 2 earthquakes to happen within the same spot or within the same plate boundary at the same time would be very unlikely i think. 2 plates build op stress between each other, and at some point this stress becomes too much and at the point where the plates have the least resistance, the plates will move to release the stress, causing an earthquake. I would say that there is always just one point within the plate boundary zone which is weakest and so where the stress will be released.

    I hope this answered you question! if anything is unclear let me know 🙂

    cheers,
    Bas

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  2. Photo: Daniel Pastor-GalánDaniel Pastor-Galán
    answered on 15 Mar 2015:

    Hi haatsuneirina,

    As Bas says, Andi is the expert. Bas mentions that they can happen, and that is right. Why not? In fact probably every day are happening Earthquakes almost at the same time, but in most of the cases very small ones. So small that we do not feel them, we know that they exist because we have great seismometers. However, taking account that big Earthquakes are rather uncommon I would say that, even it is possible that two large earthquakes happen at the same time, it is very unlikely.

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  3. Photo: Rhian MearaRhian Meara
    answered on 16 Mar 2015:

    I have one other thing to add!

    you can get what are called “aftershock earthquakes”. this is when you have a big earthquake happen and then when you think that the disaster is over, you have another earthquake which is caused by the first one. lots of people die in the afteshock earthquakes as there is already damage to buildings and people are not expecting extra earthquakes!

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  4. Photo: Andreas RudersdorfAndreas Rudersdorf
    answered on 16 Mar 2015:

    Hi Hatsuneirina,

    thank you all for believing in my expertise! 😉 I am pretty fine with all the answers from the others!

    It is indeed a game of

    – location (Where?)

    – stress state
    (How strong are the two rock packages pressing against each other?)

    – timing
    (When is the stress is so high, that the fault breaks and moves?)

    – stress transfer
    (Can the two locations “communicate” with each other?)

    …and so on and so on.

    Two earthquakes that are not related to each other can of course begin simultaneously.

    But speaking of timing you maybe want to watch this video of the 2011 Tohoku, Japan earthquake:

    (be patient, the impressive stuff happens after 40 seconds)

    Some of the smaller earthquakes begin quasi-simultaneously.

    All the best,
    Andi

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