Meteorological Agency's strong quake prediction proves wrong
The Meteorological Agency's warning that a powerful earthquake would jolt Chiba and
Ibaraki prefectures as well as downtown Tokyo early Tuesday has proven wrong.
The temblor actually registered less than one on the 7-point Japanese intensity scale. However, the warning forced Tokyo subway operators to temporarily suspend services.
Agency officials attributed the false prediction to far higher warning data than actual figures, which was sent to the quake alert system from one of the seismometers near the epicenter. The agency apologized for the error and is investigating why such erroneous data was sent to the alert system.
At around 6:37 a.m. on Tuesday, an earthquake, estimated at 4.1 on the open-ended Richter scale, jolted the Kanto region. The focus of the quake was situated about 20 kilometers below the seabed east of Chiba Prefecture.
An emergency earthquake alert system at the agency analyzes data from seismometers near the epicenter of an earthquake immediately after it occurs. If the quake is expected to register up to lower 5 on the Japanese intensity scale, it announces the areas where it is estimated to register 4 or more.
The agency warned that Tuesday's temblor would register at least lower 5 in northeastern Chiba Prefecture and southern Ibaraki Prefecture, and 4 or more in other areas of these prefectures as well as Tokyo's 23 wards among other locations.
One of four seismometers installed in the city of Minamiboso, near the quake's epicenter, showed a tremor of 25 micrometers, but data sent to the agency's emergency earthquake alert system was 525 micrometers, 21 times the actual figure.
Agency officials say they believe that the seismometer was functioning properly and have suspended the operations of the quake alert system to see why such false data was sent to the system.
(Mainichi Japan) August 25, 2009