I wanted to know if two earthquakes can happen at the same time in the same area? I "think" this can happen, but I'm not totally sure? I understand tectonic plates sliding against each other can cause an earthquake, but is it possible for two to happen at the same time in the same area?

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    $\begingroup$ It's quite possible for two earthquakes with different epicenters to occur at nearly the same time. If the epicenters are close enough, some areas will experience both earthquakes at the same time. $\endgroup$ – Barry Carter Nov 11 '16 at 4:57
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    $\begingroup$ I remember reading in a Nat Geo book that the '64 Anchorage quake was actually three separate earthquakes occurring in rapid succession. I can no longer find a source for that, however. $\endgroup$ – BillDOe Nov 11 '16 at 21:00
  • $\begingroup$ Related: physics.stackexchange.com/questions/191636/… $\endgroup$ – Tactopoda Nov 27 '16 at 1:09
  • $\begingroup$ It happens often enough that before the use of supercomputers in high resolution seismic mapping of earthquake epicenters, nuclear weapons were illicitly tested underground during nearby earthquakes. Back then, it was easy to camouflage a nuclear explosion to look like an ancillary earthquake if it happened close enough to a real earthquake in space-time. $\endgroup$ – Knob Scratcher Feb 28 '17 at 22:32
  • $\begingroup$ This is a question of definition: If two earthquakes happen in the same place at the same time, isn't that really just one big earthquake? $\endgroup$ – Spencer Jan 12 '18 at 0:16

The 2016 paper "A case for historic joint rupture of the San Andreas and San Jacinto faults" reports of research suggesting that simultaneous large earthquakes occurred in 1812 in California, the researchers used

dynamic rupture modeling to show that paleoseismic and historic observations associated with the earthquake of 8 December 1812 can be explained by joint rupture of the SAF and SJF.

(SAF = San Andreas Fault and SJF = San Jacinto Fault)

But the author stresses that what they have is a model, rather than a certainty.

Alot of research centres around the notion of 'near-simultaneous earthquakes', such as the 2009 South Pacific earthquake, as described in the article "Double Shake: Multiple, Nearly Simultaneous Earthquakes Triggered Deadly 2009 Tsunami" where studies suggest that at least 2 quakes of similar magnitude occurred within 50km of eachother, separated by minutes - another similar study suggests that one of the quakes 'obscured' another nearby rupture of equal or higher magnitude.

Italy is another place where simultaneous or near-simultaneous earthquakes seem to occur and resulted in several studies, one of which being reported in the article "Likely near-simultaneous earthquakes complicate seismic hazard planning for Italy", stating that

It's very important to consider this scenario of earthquakes, occurring possibly seconds apart, one immediately after another

Stating that this scenario would have an 'amplification' effect of the the effects of the shhaking (hence, the researchers' concern). A particular example they cite is

The 1980 Irpinia earthquakes included a sequence of three events, occurring at intervals within 20 seconds of each other.

Another compelling example, reported in the article "Sumatran strike-slip earthquakes challenge seismologists" that occurred in April, 2012 - a strike-slip fault induced quake of a magnitude of 8.6 on the richter Scale, one of the theories for the great magnitude is explained as

Another apparent reason for the large magnitude, says Miaki Ishii, a sesimologist at Harvard University, is that multiple faults appear to have slipped almost simultaneously, creating a composite earthquake. “If it was just a single fault activation, it wouldn’t have been large as 8.6.

An important note the Harvard seismologist makes, that essentially answers your question regarding simultaneous (and near-simulatneous earthquakes), is that observations of this kind of fault activation, which is described as "a cascading failure of faults" are seen in a lot of large earthquakes.

  • $\begingroup$ Is this another example? $\endgroup$ – uhoh Nov 19 '16 at 12:03
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    $\begingroup$ @uhoh yes, I would think that would be a very good and recent example (good question too!) $\endgroup$ – user7009 Nov 19 '16 at 12:07

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