Earthquakes in Japan, Chile, Haiti: Are We In An Age Of Giant Quakes?

April 8, 2011— -- The devastating 2004 Indonesian tsunami, with its death toll of as many as 250,000 people, was caused by the first magnitude-9.0 earthquake since 1967. A succession of smaller but still destructive tremors in Haiti, Chile, and New Zealand -- surpassed by this year's magnitude-9.0 quake in Japan -- has some researchers wondering whether the number of large earthquakes is on the rise.

An earthquake represents the abrupt release of seismic strain that has built up over the years as plates of the Earth's crust slowly grind and catch against each other. Giant earthquakes live up to their fearsome name. The biggest ever recorded was the magnitude-9.5 Chile earthquake of 1960. It accounts for about a quarter of the total seismic strain released worldwide since 1900. In just three minutes, the recent quake in Japan unleashed one-twentieth of that global total according to geophysicist Richard Aster at the New Mexico Institute of Mining and Technology in Socorro.

The Indonesian quake "reinvigorated interest in these giants," said Aster, who is also president of the Seismological Society of America. The Chile and Japan earthquakes -- along with a magnitude-9.2 quake in Alaska in 1964 -- also triggered catastrophic tsunamis.

After a lull in large quakes in the 1980s and 1990s, we may now be in the middle of a new age of large earthquakes, Aster added.

Records from the past century reveal some periods that have seen an unusual number of giant earthquakes, defined as those with magnitude 8.0 or higher. For example, global seismic data show a dramatic spike in the rate of large earthquakes from 1950-67. But there have also been quiet periods with fewer large quakes. And with only 100 years worth of records to consult, researchers aren't sure what these patterns of large quakes might mean -- or whether they mean anything at all.

Even if clusters of giant earthquakes are a real phenomenon, Aster noted, researchers don't have any good ideas on how one big quake can trigger another big one in a different part of the world.