Is it true that a series of small earthquakes help prevent a large eartquake?

  1. Is it true that a series of small magnitude earthquakes help prevent a large magnitude eartquake? Aren't earthquakes basically independent events from a statistical point of view?
  2. jcsd
  3. Yes it is true, usually. Smaller earthquakes let out some of the pressure built up along a fault line.

    The amount of slippage depends on the force integrated since the time of the last slippage. If a fault sticks for a very long time, for whatever reason, the amount of energy released will be greater as energy released is proportional to distanceXmass of the moved plate.
  4. Drakkith

    Staff: Mentor

    My knowledge of plate tectonics and related areas isn't really that great, but I would think that a series of small earthquakes could prevent a larger one if it allows the stress between the two plates to be released gradually instead of all at once.
  5. Interestingly, when there is slippage between points A and B on a fault, additional stress builds up along the fault just beyond points A and B. You can imagine this as just inside points A and B there has been some movement, but just outside no movement, and this difference in movement in a solid body produces shear strain.

    I think this is the usual cause of afterschocks, which are smaller earthquakes following a larger one.
  6. berkeman

    Staff: Mentor

    I think we are going to need to see some peer-reviewed research posted here, before we can make statements like this. I used to believe that what you say is true, but then I read in a credible paper that it is not true. I'll see if I can find that paper, but if you have mainstream research showing that minor quakes help to prevent larger ones on the same fault, I'd like to read it.

    (I live on the Hayward Fault in Northern California, BTW...)
  7. Unfortunately what I learned in Grade 11 Geology did not come with provided peer reviewed articles, so I can't give you direct source on that.

    It's possible what they teach in school is wrong.
  8. berkeman

    Staff: Mentor

    I think I found where I learned that it is false -- at the USGS website:

  9. What I'm seeing from this site:

    Indicates that preceding earthquakes do relieve pressure along a fault, however most cases there are an insufficient number of them to significantly postpone the larger quake that follows.

    Just goes to show that if intuition were at all accurate, we wouldnt need science.
  10. davenn

    davenn 4,353
    Science Advisor
    Gold Member
    2014 Award

    be a little wary of what you are posting ;)

    The aftershock sequence is use to define the rupture zone of a quake
    The areas outside that zone where stress has been transferred to is where you can look to the probability of future events that will occur usually well before the "return period' of the zone that has just ruptured.

    Aftershocks are basically the readjusting of stresses within the rupture zone. You need to realise that fault systems are rarely a simple single plane that slips. and that the system is most likely made up of multiple large and small faults. All of these intertwined faults can produce aftershocks as the stresses are released within the area.

  11. If you haven't already read this, six Italian scientists have been convicted of involuntary manslaughter because they were "criminally mistaken" in "falsely reassuring" people that major earthquake is unlikely after series of some low-level tremors.
  12. berkeman

    Staff: Mentor

    There is a long thread about this in the General Discussion forum. Please keep discussions about this subject in that thread:

    Thank you.
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