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How Long After an Earthquake Can Aftershocks Hit?

Aftershocks are smaller followup quakes that are mostly thought to hit within two days after an initial earthquake. Some aftershocks may occur days or even weeks later. Repeated aftershocks over an extended period of time are more likely after large, destructive earthquakes. Although uncommon, possible cases of aftershocks have been reported years after an earthquake. For example, some researchers argue that the small earthquakes in China's Tangshan region in 2012 may actually have been aftershocks from the Tangshan Earthquake of 1976.

More quake facts:

  • Aftershocks tend to be less powerful than earthquakes, but have the ability to destroy bridges, buildings, and roads.

  • China refused all international relief aid after the 1976 Tangshan Earthquake, which is thought to have contributed to the death toll of over 240,000. By the time the suspected 2012 aftershocks occurred, this policy had been overturned.

  • A frequently used formula to attempt to predict aftershocks is Omori’s Law, which states that the likelihood of an aftershock decreases by the reciprocal of the number of days after an earthquake. For example, the odds of an aftershock two days after an earthquake would be one in two, and by day 10 the probability would decrease to a one in 10 chance.

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More Info: agu.org

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