Japan Earthquake Not the “Big One”?
Megaquake long predicted—but in totally different region.
Richard A. Lovett
Though Friday’s Japan earthquake—which spawned a tsunami and damaged a nuclear power plant—was the largest to strike the country since the dawn of modern seismology, it wasn’t the long dreaded “big one,” experts say.
Not because the magnitude 9 earthquake wasn’t big, but because it was in the wrong place. (See Japan earthquake and tsunami pictures.)
Seismologists have long predicted that the big one would probably be a repeat of the 1923 Kanto earthquake, which occurred in a dangerous fault zone close to Tokyo and killed an estimated 142,000 people.
Japan is a tectonically complex zone where three major plates, the Pacific plate, the Okhotsk plate, and the Philippine plate are all ramming into each other. (Learn more about tectonic plates.)
The 1923 earthquake—estimated to have had a magnitude of between 7.9 and 8.4—came from the collision between the Philippine plate and the islands of Japan, in a fault zone known as the Sagami Trough, offshore from Tokyo.
Last week’s earthquake occurred farther north, in the southern part of the Japan Trench, formed by the collision of the Pacific and Okhotsk plates.
“Most [experts] didn’t expect one so big from there,” Chris Goldfinger, director of the Active Tectonics and Seafloor Mapping Laboratory at Oregon State University, said by email.