"Long before it's in the papers"
January 27, 2015


Spate of recent big quakes looks like a fluke, scientists say

Aug. 2, 2012
Courtesy of the Seismological Society of America
and World Science staff

A spate of re­cent, large earth­quakes ap­pears to be just a fluke, and thus un­likely to con­tin­ue, sci­en­tists have con­clud­ed.

The past dec­ade has been plagued with what seems to be a clus­ter of large earth­quakes, with mas­sive quakes strik­ing Su­ma­tra, Chil­e, Hai­ti and Ja­pan since 2004. Some re­search­ers have sug­gested this clus­ter has oc­curred be­cause the earth­quakes may be “com­mu­ni­cat­ing” across large dis­tances, pos­sibly trig­ger­ing each oth­er.

But the new anal­y­sis by Tom Par­sons and Er­ic Geist of the U.S. Ge­o­log­i­cal Sur­vey con­cludes that the clus­ter could just as well be the re­sult of chance.

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 trig­ger oth­ers across the world, Par­sons and Geist say, in or­der to pre­dict wheth­er more se­verely de­struc­tive quakes might be on the way.

To de­ter­mine if quake clus­ters in the 1960s and 2000s could be at­trib­ut­ed to 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: in oth­er words, the glob­al haz­ard of large earth­quakes is un­changed. Ex­cept in the case of lo­cal af­ter­shocks, the prob­a­bil­ity of a new large quake oc­curring is­n’t re­lat­ed to past glob­al quakes.

This could be dis­ap­point­ing news for re­search­ers who thought glob­al com­mu­nica­t­ion be­tween quakes might of­fer a way to pre­dict the most se­vere seis­mic ac­ti­vity. But there al­so may be some good news af­ter a dec­ade of de­struc­tion, the scien­tists said: if great quakes 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.

The find­ings are pub­lished in the Bul­le­tin of the Seis­mo­log­i­cal So­ci­e­ty of Amer­i­ca.

* * *

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A spate of recent, large earthquakes appears to be just a fluke, and thus unlikely to continue, scientists have concluded. The past decade has been plagued with what seems to be a cluster of large earthquakes, with massive quakes striking Sumatra, Chile, Haiti and Japan since 2004. Some researchers have suggested this cluster has occurred because the earthquakes may be “communicating” across large distances, possibly triggering each other. But the new analysis by Tom Parsons and Eric Geist of the U.S. Geological Survey concludes that the cluster could just as well be the result of chance. 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 trigger others across the world, Parsons and Geist say, in order to predict whether more severely destructive quakes might be on the way. To determine if the quake clusters in the 1960s and 2000s could be attributed to 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: in other words, the global hazard of large earthquakes is unchanged. Except in the case of local aftershocks, the probability of a new large quake occurring isn’t related to past global quakes. This could be disappointing news for researchers who thought global communication between quakes might offer a way to predict the most severe seismic activity. But there also may be some good news after a decade of destruction. If global great earthquakes are occurring at random, the authors say, 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. The findings are published in the Bulletin of the Seismological Society of America.