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Scott G. Winterton, Scott G. Winterton, Deseret News
Keith Koper, director of University of Utah Seismograph Stations, says that large earthquakes can occur in clusters.

SALT LAKE CITY — The earthquake that struck Sendai, Japan, was the fifth-strongest temblor in the past century.

The magnitude 8.9 quake was the fourth in the past 10 years with a magnitude of at least 8.0. Prior to 2004, the last such major seismic event occurred when a 9.2 quake struck Alaska in 1964, according to Ron Harris, professor of geology at BYU.

"It was a time of seismic quiescence in terms of large events," he said. "(Now) there has been a cluster of these events that have happened in the last decade."

Harris said contrary to what recent evidence might suggest, earthquakes have not gotten stronger of late, the spate of major quakes is rather coincidental. Prior to ’64, there had been another period of "seismic storm." Unfortunately, the more recent events have had especially devastating consequences.

Another local geological expert concurred.

"Earthquakes are essentially random," said Keith Koper, the director of the University of Utah Seismograph Stations. "You expect to have clusters in a random process."

He said just as stars are randomly grouped in the night sky, with areas of sky virtually empty and others filled with bright lights, seismic events can occur in clusters over some periods and seldom in others.

"The thing that would be really unusual is if we had a magnitude 8.0 (quake) every year, once a year," Koper said. "What we see now is an uptick, but it's what we expect from the chaotic random nature of the big earthquakes."

Based on scientific data, the Sendai quake struck deep under the ocean and lasted for 150 seconds — a seismic eternity.

Koper said the deep sea geologic "rupture probably moved over an area covering hundreds of kilometers."

"This was a massive, massive, massive earthquake," he said.

Likening the event to unzipping a sleeping bag, Koper explained, "You can imagine that the zipper has moved for 150 seconds and while it's doing that, energy is being generated in seismic waves (moving outward). … It’s a serious event."

The 8.9 quake launched a tsunami that wreaked devastation across Japan's eastern coast, destroying buildings, roadways and killing hundreds near Sendai, Myagi, prefecture.

"When you see these buildings floating inland and they've been decoupled from the ground and you have this big mass of water, it's terrifying," Koper said.

Katherine Whidden, research seismologist at the University of Utah, said Japan sits on top of two tectonic plates that press together deep underground. Enormous pressure forces one plate to slide beneath the other resulting in "the largest earthquakes in the world."

While Japan has had only one of the top 10 magnitude quakes since 1900, the densely populated island nation has experienced numerous large-scale events over the years resulting in thousands of fatalities and billions of dollars in damage.

She said the Friday event spawned 10-meter waves all long the coastline and even prompted emergency alerts as far away as Hawaii and the West coast of the U.S. mainland. Luckily, states such as California, Oregon and Washington were spared any major wave damage.

Meanwhile, in Japan, Whidden said residents could expect to experience significant aftershocks for months to come.

"The good news is Japan is probably the best prepared country in the world for large earthquakes," she said. "(The bad news is) there is definitely the potential for more large earthquakes." 

E-mail: jlee@desnews.com