By Julian Ryall in Tokyo for Telegraph.co.uk
3:08 BST 13 Aug 2009
The earthquake had a magnitude of 6.5 and originated 40 km below the surface of the sea off Hachijo Island, south of Tokyo. The tremor on Tuesday morning, in which a woman was killed when a bookcase collapsed on her and 110 people were injured, was a short way to the west.
The earthquake, also measuring 6.5, was the largest in Shizuoka Prefecture since 1944 and forced the emergency shut-down of two nuclear reactors, caused a 60 cm tsunami to hit local beaches and damaged road and rail links.
But officials of the Japan Meteorological Agency said the tremors are not indicators of the quake that the region has been bracing itself for over the last 20 years.
Major movements in the crust of the Earth have occurred in the Tokai region, close to the major city of Nagoya, on average every 110 years. The last one with a magnitude of 8 was 155 years ago.
Researchers now put the likelihood of a serious earthquake - one that could cause around 6,000 deaths, 20,000 serious injuries and damage to 1 million buildings - within the next 30 years as high as 87 per cent.
"Old records show that there have been a series of gigantic quakes in this area," said Yohei Hasegawa, a spokesman for the agency's Earthquake and Tsunami Observation Division.
"In some cases, we know there are precursors and we hope that the early-warning system that was introduced in October 2007 will be able to give local people up to 20 seconds to prepare," he said.
Made up of a series of sensitive strain meters, seismographs and tilt meters, the warning system failed to issue a warning for any of the recent quakes because the energy emitted by a precursor wave was too small to be picked up, Hasegawa said.
"The quake on Tuesday was 6.5 and while in other countries that might be considered quite big, it was not so serious here in Japan," he said.
"If we could detect the precursors of smaller earthquakes, that would be ideal, but I don't think it's practical at the moment," he said. "This is a very difficult science and I have never heard of a researcher claiming to be able to detect a precursor to such a small earthquake."
Meanwhile, the government has been forced to downplay the failure of its early-warning alarm system, which did not detect Tuesday's quake.A collapsed section of the Tomei Expressway in
Makinohara, on August 11 (Photo: AFP)
TOKYO — A strong offshore earthquake jolted central Japan, including Tokyo, on Thursday, just two days after a powerful tremor left one person dead and 120 injured.
The 6.7-magnitude quake struck at 07:49 am (2249 GMT) in the Pacific Ocean, some 325 kilometres (202 miles) southeast of the capital, according to the US Geological Survey.
The Japanese meteorological agency did not issue a tsunami warning, and no immediate damage was reported.
An earthquake of magnitude 6.4 struck central Japan on Tuesday, damaging nearly 5,200 buildings and a section of the arterial road linking Tokyo with the western city of Osaka.
Construction workers for Central Nippon Expressway Co., which operates the Tomei Expressway, scrambled to repair the section damaged in a landslide before the weekend, a major summer holiday break in Japan.
But the company said it will take at least until Saturday before the highway will fully reopen.
Around 20 percent of the world's most powerful earthquakes strike Japan, which is located at the intersection of several tectonic plates.
Japanese rescuers and troops also continued searching for 10 people still missing after Typhoon Etau brought torrential rains to western Japan earlier this week, which left at least 19 people dead in landslides and floods.