Possible Large Earthquake Warning for Tokyo Area
August 31, 2011 • 9:23AM

An increased frequency of small earthquakes in the Tokyo area since the great March 11 quake to the North, raises the "possibility of a huge plate-boundary earthquake amplified by simultaneous moves in two or more focal areas," according to the University of Tokyo's Earthquake Research Institute. The institute said that since the March 11 disaster, pressure on the tectonic plates beneath the city has changed and two or more focal areas may move simultaneously, resulting in a massive quake.

The number of small-scale plate-boundary quakes that are not felt by people has drastically increased following the March 11 earthquake: the number of magnitude-3 or larger plate-boundary quakes between March 11 and Aug. 20 rose about fourfold in an area 60 to 70 kilometers below northern Tokyo Bay. Similarly sized plate-boundary quakes occurring 40 to 55 kilometers below southern Ibaraki Prefecture, an area about 100 miles to the Northeast of Tokyo, have increased about 20-fold. Inland of Tokyo, the frequency of quakes has not changed, but they are of different character.

It is not known if electro-magnetic, satellite-based, or other types of non-seismic precursor measurements are available to enhance this information.