Japan’s catastrophic March 11 earthquake was the biggest ever recorded in Japan and the costliest natural disaster in history, but in a way it was nothing new. Three other quakes of magnitude 8.6 or greater have struck worldwide in the past seven years — after a gap of four decades.
Two U.S. Geological Survey scientists contend that the Japan quake bolsters their idea that the planet is experiencing a spasm of great earthquakes, its second since 1900. Other scientists say that any apparent bunching is a statistical fluke that disappears if the data are analyzed in other ways. Researchers presented their opposing views on April 14 in Memphis, Tenn., at the annual meeting of the Seismological Society of America.
On the face of it, large quakes certainly do seem to have been popping off lately. The magnitude 9.1 Sumatra quake in 2004, which caused the disastrous Indian Ocean tsunami, was followed by a nearby magnitude 8.6 the following year. A magnitude 8.8 hit Chile in February 2010 and the Japan quake struck on March 11 of this year, leading many to question whether big quakes are becoming more frequent.