Tokyo quake fault line is re-evaluated

July 15, 2005

A new survey suggests the fault line beneath Tokyo is miles closer to the surface than seismologists realized, reported Thursday.

Seismologists might not have accurately determined the depth of Tokyo's fault line since jolts at the interface of the two plates are quite rare, said Hiroshi Sato of the University of Tokyo's Earthquake Research Institute. Sato led the new study.

He and his colleagues sent vibrations into the ground from trucks, air guns and explosives, reported. The scientists then examined the pattern of the waves that bounced back to determine the composition of the sub-surface rocks.

They determined the fault line is between two miles and 16 miles below the city, the researchers report in this week's Science1. Previously, seismologists estimated the fault line depth at 12-to-25 miles.

Sato said the new findings might mean an earthquake occurring at the fault line might cause more extensive damage than previously thought.

Scientists said the study will have to be replicated, since Sato might have seen waves bouncing off a fault offshoot running closer to the surface, rather than from the main fault.

Copyright 2005 by United Press International

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