Planet has unusual period of silence between large earthquakes

April 24, 2013 GEOLOGY In the global aftershock zone that followed the major April 2012 Indian Ocean earthquake, seismologists noticed an unusual pattern. The magnitude (M) 8.6 earthquake, a strike-slip event at intra-oceanic tectonic plates, caused global seismic rates of M=4.5 to rise for several days, even at distances thousands of kilometers from the main-shock site. However, the rate of M=6.5 seismic activity subsequently dropped to zero for the next 95 days. This period of quiet, without a large quake, has been a rare event in the past century. So why did this period of quiet occur? In his research presentation, Fred Pollitz of the U.S. Geological Survey suggests that the Indian Ocean earthquake caused short-term dynamic stressing of a global faulting system. Across the planet, there are faults that are “close to failure” and ready to rupture. It may be, suggests Pollitz and his colleagues, that a large quake encourages short-term triggering of these close-to-failure faults but also relieves some of the stress that has built up along these faults. Large magnitude events would not occur until tectonic movement loads stress back on to the faults at the ready-to-fail levels they reached before the main shock. Using a statistical model of global seismicity, Pollitz and his colleagues show that a transient seismic perturbation of the size of the April 2012 global aftershock would inhibit rupture in 88 percent of their possible M=6.5 earthquake fault sources over the next 95 days, regardless of how close they were to failure beforehand. –SD
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3 Responses to Planet has unusual period of silence between large earthquakes

  1. wayne pearson says:

    Alvin, there has just been in the last hour another MAJOR earthquake. This time in the New Ireland Region of Papua New Guinea at a very shallow depth of 17.8 Kilometres according to the United States Geological Survey at a magnitude of 6.4 on the richter scale. Geoscience Australia recorded the quake at a magnitude of 6.5 at a very shallow depth of 5 Kilometres. This is now the FIFTEENTH MAJOR or GREAT quake in the last 19 days.

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  2. Louise Page says:

    My take on what is said in this article and what I feel, is that I tend to think that a major event occurs (because of built up stress – then release), and the reverberations of such can disturb already jittery faults and those which just need such a reverberation to set them off.
    The power (energy) released from a large quake is thus transferred through to other faults, where some will give and others (more stable) will just be slightly irritated. Regular irritation may set some off at a later stage.
    Sometimes the actions of volcanoes and the underlying magma movements contribute, may relate and/or may provide (re: fluidity) some impetus for plate/earth shifting.
    The relative seismic ‘quiet’ following major movements may be due to stabilizing of the various energies, post-release, only to gradually build over time as further energy shifts compound – to again release and give in various places. There can be quicker energy build-up with periods of M5’s or M5+’s coming as somewhat of a surprise on occasions as nature doesn’t always ‘follow’ a predictable energy build- and- release clock.
    Some EQ’s can be pre-empted when one studies the behaviour of seismographs daily.
    Mother Nature never ceases to amaze me.
    Peace to all

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