Toledo Legal News - News OSU study notes 'wobble' effect in Japan earthquake
In the months leading up to the magnitude-9 earthquake that shook Japan in 2011 and triggered a devastating tsunami, the island land masses shifted back and forth, an Ohio State University researcher said in a new study.
Published recently in Nature, the research described a "wobble" that may have the potential to alert seismologists to greater risk of impending, large-scale subduction-zone earthquakes - those in which a tectonic plate slides underneath another one.
The underthrusting action jams up or binds the earth, until the jam is finally torn or broken, resulting in an earthquake, the study found.
"What happened in Japan was an enormous but very slow wobble - something never observed before," said study co-author Michael Bevis, professor of earth sciences at The Ohio State University. "But are all giant earthquakes preceded by wobbles of this kind? We don't know because we don't have enough data.
"This is one more thing to watch for when assessing seismic risk in subduction zones like those in Japan, Sumatra, the Andes and Alaska."
The wobble would have been imperceptible - just a few millimeters each month during a five- to seven-month period - to people standing on the island, he said.
The research team, which included scientists from Germany, Chile and United States, analyzed that data and saw a reversing shift in the land - movements markedly different from the steady and cyclical shifts the Earth's land masses continuously make, a press release detailed
"The world is broken up into plates that are always moving in one way or another," Bevis said. "Movement is not unusual. It's this style of movement that's unusual."
Bevis said the wobble could indicate that in the months before the earthquake, the plate under the Philippine Sea began something called a "slow slip event," a relatively gentle and "silent" underthrusting of two adjacent oceanic plates beneath Japan, that eventually triggered a massive westward and downward lurch that drove the Pacific plate and slab under Japan, generating powerful seismic waves that shook the whole country.
The 2011 earthquake caused widespread damage throughout Japan, permanently shifting large parts of Japan's main island, Honshu, several meters to the east.
It launched tsunami waves in excess of 130 feet high, displacing more than 450,000 people and causing the melt down of several nuclear reactors at the Fukushima Daiichi Nuclear Power Plant.
Researchers who study earthquakes and plate tectonics try to pinpoint the approximate magnitude of the next large earthquakes and predict where and when they might occur.
Application of the study's findings won't be possible at all subduction zones around the world as the GPS systems don't exist in all of the areas, said the study's lead author Jonathan Bedford, a researcher at the GFZ German Research Centre for Geosciences.
He noted that Japan had one of the largest and most robust GPS monitoring systems in the world at the time of the temblor.
That system provided ample data, and allowed the research team to identify the swing the land mass made in the months leading up to the earthquake.
Other countries, including Chile and Sumatra, which were hit by devastating earthquakes and tsunamis in 2010 and 2004, respectively, had much less-comprehensive systems at the time of those disasters.
The researchers analyzed similar data from the 2010 Chile earthquake, and found evidence of a similar wobble; Bedford said the data was "only just good enough to capture the signal."
"We really need to be monitoring all major subduction zones with high-density GPS networks as soon as possible," he said.