The recent cluster of huge quakes around the Pacific Ocean has fueled speculation that they are seismically linked.

The December 2004 Sumatra quake, the February 2010 Chile quake, and now, Sendai have struck in just over six years. This presents a horrifying possibility: that there is a link between these megaquakes and that, as a result, more could strike.

What is clear is that for the 6.2 years since 2004, there have been more great earthquakes around the world than in any 6.2-year period throughout the 110-year history of seismic recordings,” says Thorne Lay at the University of California, Santa Cruz. He cites specific doublets — pairs of comparably large quakes that happen on the same or neighboring faults within months of each other.