Reading media accounts, it seems the past decade has witnessed what seems to be a cluster of large earthquakes, with massive events in Sumatra, Chile, Haiti and Japan since 2004.

Some hypothesize that this cluster has occurred because the earthquakes may be "communicating" across large distances, possibly triggering each other. 

Each of the devastating quakes in the 2000s drew huge media coverage and required extensive rebuilding and economic restoration. The intense interest in the earthquakes has led some to wonder if we are living in the middle of an "age of great quakes," similar to a global cluster of quakes in the 1960s. It's important to know whether these clusters occur because big earthquakes can trigger others across the world, say
Tom Parsons and Eric Geist of the US Geological Survey, and predicting whether more severely destructive quakes might be on the way is important.

To determine if the quake clusters in the 1960s and 2000s were clusters or random chance, the researchers looked at the timing between the world's largest earthquakes - magnitude 8.3 and above- at one-year intervals during the past 100 years. They compared simulated lists of large quakes and the list of real quakes during this time with the between-quake intervals expected from a random process.

The intervals between the real-life large quakes are similar to what would be expected from a random process, they found, they found. In other words, the global hazard of large earthquakes is constant in time. Except in the case of local aftershocks, the probability of a new large quake occurring isn't related to past global quakes.

It's disappointing news for researchers who believe global communication between quakes might offer a way to predict the most severe seismic activity but it's good news for everyone else.  Since global great earthquakes are occurring at random, then a specific number of quakes that cluster together within a short time is unlikely to be repeated in a similar way over a 100-year span.

Published in Bulletin of the Seismological Society of America