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Tokyo at risk from massive aftershock, expert says

March 15, 2011

John Rundle on Tokyo earthquake

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Videography by Academic Technology Services/MediaWorks

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Earthquakes in the past 110 years

This video, made with KeckCAVES visualization software, first shows global earthquakes over the past 110 years (green dots) then zooms in on Japan to show earthquakes in the past week. Green dots are the smallest earthquakes and red the largest.

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Videography by Cara Harwood, Oliver Kreylos, Braden Pellett and Louise Kellogg

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[Editor's note: UC Davis has many more media experts on the Japanese earthquake and tsunami.]

Tokyo may be at serious risk from a massive aftershock and associated tsunami as a result of the devastating March 11 earthquake near Sendai, Japan, according to UC Davis seismologist John Rundle.

Friday's magnitude 9.0 temblor has been followed by hundreds of powerful aftershocks that have migrated southwards, noted Rundle, who is professor of geology and physics at UC Davis.

"Initially, the major aftershocks were confined to the region near Sendai, but the steady southward march of the aftershocks is cause for alarm for Tokyo and surrounding regions," Rundle said.

There is historical evidence of major earthquakes off the coast of Japan being followed by another similarly large earthquake nearby within a relatively short period of time, he said.

These include the magnitude 8.4 Ansei-Nankai and Ansei-Tokai earthquakes of 1854, separated in time by only 31 hours; and the 1944-1946 Tononkai and Nankai earthquakes, with magnitudes of 8.0 and 8.1, respectively. Typically, an earthquake of magnitude 9 would be followed, in no particular order, by one aftershock of magnitude 8, ten aftershocks of about magnitude 7 and many smaller aftershocks.

That 8.0 aftershock has yet to occur. If it happened in Tokyo Bay, it could set off a tsunami that would devastate the densely populated region, similar to the events of September 1, 1923 during the great Kanto earthquake (magnitude 7.9).

Rundle's research uses computer modeling to understand systems that can go through abrupt and catastrophic changes, such as earthquake faults and financial markets. He has collaborated with researchers at NASA's Jet Propulsion Laboratory and other universities on Quakesim, which studies earthquake fault systems and has produced earthquake forecasts for California and other parts of the world.

In a blog entry posted July 30 on the website Openhazards.com, Rundle forecast that of four Japanese cities -- Tokyo, Osaka, Niigata and Sendai -- Sendai was the second-most likely to be hit by a major earthquake within 150 miles over the next year. Tokyo was the most at risk, he calculated. He has updated this forecast as of 3 p.m. on March 13.

In addition to his research and teaching position at UC Davis, Rundle is the co-founder of Openhazards.com, a startup company that provides earthquake forecasting and hazard analysis services to the public, homeowners and businesses.

About UC Davis

UC Davis is a global community of individuals united to better humanity and our natural world while seeking solutions to some of our most pressing challenges. Located near the California state capital, UC Davis has more than 34,000 students, and the full-time equivalent of 4,100 faculty and other academics and 17,400 staff. The campus has an annual research budget of over $750 million, a comprehensive health system and about two dozen specialized research centers. The university offers interdisciplinary graduate study and 99 undergraduate majors in four colleges and six professional schools.

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