Japan Rocked By New Earthquake

An earthquake off the north-east coast of Japan puts the region on high alert, but a tsunami warning is lifted after 90 minutes.

Japan: Earthquake prompts Fukushima evacuation

Authorities in north-east Japan ordered a general evacuation and workers at the damaged Fukushima Daiichi nuclear plant took shelter after an earthquake triggered a new tsunami warning.

However, the tsunami warning was lifted after 90 minutes and the earthquake - with a magnitude of 7.1 - did little obvious damage.

Fukushima officials said the quake had no detectable effect at the plant.

Last month's 9.0 earthquake set off a tsunami which devastated the region.

Shelter

The earthquake - at a depth of 49km (32 miles) - struck off Japan's north-east coast, close to the epicentre of the 11 March quake.

All seven of the workers at Fukushima Daiichi were safe, a spokesman for plant operator Tepco told a news conference in Tokyo.

"They have not been injured and they have all taken shelter in our seismic-resistant building. We are continuing to inject water, or we are continuing the injection operation at reactors 1, 2 and 3," said the spokesman, whose name was not given.

The workers are trying to keep the damaged reactors cool to stop further releases of radioactive material.

Thursday's quake struck at 2332 local time (1432 GMT) on Thursday, 118km (78 miles) north of Fukushima, 40km offshore.

First reports said it had a magnitude of 7.4 but that was later revised downwards to 7.1, according to the US Geological Survey (USGS).

Last month's earthquake had a magnitude of 9.0 and struck at 32km deep.

USGS geophysicist Paul Caruso said Thursday's quake struck at about the same location as the 11 March quake, the AP news agency reported.

The quake was strong enough to shake buildings in Tokyo, 265km to the south.

"The earthquake was moving in an up-and-down motion," Miri Gono in Tokyo told the BBC by e-mail. It started off with small shakes, then shook bigger. I was alone in my house with my brother and we were so scared... We took our bottles of water and hid under the table."

Japan's meteorological agency issued tsunami warnings and advisories for a stretch of coast 420km long, from Aomori prefecture in the north to Ibaraki prefecture in central Japan, just north of Tokyo.

Hundreds of aftershocks have shaken north-eastern Japan in the wake of the earlier earthquake, but few have measured higher than 7.0.

About 28,000 people are dead or missing, and hundreds of thousands were left homeless after the tsunami which ripped through north-eastern Japan.

Caesium fallout from Fukushima rivals Chernobyl

Radiation levels in towns north of the stricken reactor are

particularly high (Image: Christian Alund/Greenpeace)

The readings were taken by the Japanese science ministry, MEXT, and reveal high levels of caesium-137 and iodine-131 outside the 30-kilometre evacuation zone, mostly to the north-north-west.
Iodine-131, with a half-life of eight days, should disappear in a matter of weeks. The bigger worry concerns caesium-137, which has a half-life of 30 years and could pose a health threat for far longer. Just how serious that will be depends on where it lands, and whether remediation measures are possible.
The US Department of Energy has been surveying the area with an airborne gamma radiation detector. It reports that most of the "elevated readings" are within 40 kilometres of the plant, but that "an area of greater radiation extending north-

west… may be of interest to public safety officials".

$6.8 billion needed to ready US for the next big quake

How a 7.8-magnitude earthquake might spread

along the San Andreas fault (Image: David McNew/Getty)

The recent magnitude-9.1 megaquake and the tsunami that followed it showed that Japan was not fully prepared for so violent a tremor. If even a country that suffers frequent earthquakes wasn't ready, what of the US, which itself contains several seismic hotspots?

Over the past two decades, the US has made considerable advances in fortifying its cities against quakes, but geologists and engineers agree that there is still much to be done. In a National Research Council (NRC) report published today, they have outlined just what that means.

The National Earthquake Resilience report is particularly concerned with the possibility of a "Katrina-like earthquake": not just a moderately damaging tremor, but a cataclysm rivalling the 1906 San Francisco quake, estimated at magnitude 7.9, which probably led to thousands of deaths.

Geologists fear that because of the US's relatively unshaken recent history, its citizens have been lulled into a false sense of security, believing that a devastating earthquake is unlikely to strike the country – although it's not even 50 years since Alaska felt the force of the second largest quake in recorded history. The magnitude-9.2 Prince William sound event led to 115 deaths in Alaska alone.

The NRC report recommends three major goals: raising understanding of earthquakes; developing cost-effective measures to reduce the effects of earthquakes on individuals, the built environment and society at large; and improving the earthquake resilience of communities nationwide. Over 20 years, reaching those goals is likely to cost $6.8 billion.

Lessons from Japan's Earthquake

Science Daily (Mar. 14, 2011) — While Japan's 8.9-magnitude earthquake and accompanying tsunami represent a devastating natural disaster for the country's residents, scientists should also seize upon the massive temblor as an important learning tool for future quakes around the world, including the Pacific Northwest coast of the United States, according to experts from the Woods Hole Oceanographic Institution (WHOI).

WHOI geophysicist Jeff McGuire said such lessons may be particularly germane to residents of Northern California, Oregon, Washington and Vancouver--a region he said, could be subject to a similar quake/tsunami scenario. "Today's earthquake happened on a subduction zone thrust fault where the Pacific plate subducts, or dives, under the Japanese islands," he said. "Japan regularly has large earthquakes and tsunamis all along its east coast due to subduction.

"The west coast of the U.S., offshore of Oregon, Washington, Northern California, and Vancouver Island Canada, has a similar subduction zone that we think had similar size earthquakes regularly in the past, based on geologic evidence. The last one was in AD 1700, and they have a 250- to 500-year repeat time. There are no historical records from Oregon/Washington at that time, but the tsunami it generated was so large that it killed people in Japan."

McGuire has also studied foreshocks extensively, a phenomenon in which a smaller quake seems to foreshadow a larger one. "A few percent of earthquakes will trigger an event that is larger than the first event," he said.

That scenario may have been at work in the Japan quake -- formally identified as the N Honshu earthquake, according to WHOI Senior Scientist Jian Lin, currently on a research cruise in the Southern Ocean aboard the Korean icebreaker R/V Araon. Lin noted that a sizeable foreshock preceded the Japan quake.

"What is noticeable about the March 11, 2011 quake is that there was a magnitude 7.2 foreshock [on March 9], which is only 40 kilometers (km) away from the epicenter of the mainshock," said Lin, who has studied large quakes extensively, including last year's major quakes in Haiti and Chile.

"Foreshocks have been used previously as a tool for forecasting larger earthquakes," he said. "I am sure that we will be looking closely at this and other foreshocks."

The Araon started its mission in Christchurch, New Zealand, which experienced its own damaging earthquake this February. Now, heading back to Christchurch, it may encounter the remnants of the Japan tsunami -- albeit perhaps barely noticeable at the ship's current location. "Our cruise started with the Christchurch earthquake in New Zealand, and ends in sailing through a tsunami caused by the great Japan earthquake," Lin said.

The magnitude 8.9 quake struck 125 km off shore and about 370 km northeast of Tokyo, Lin said. It is likely to be the fifth largest earthquake ever recorded by instruments, he added.

Working on shipboard computers, Lin said that as of Friday afternoon, March 11, "I have already received notes of more than 40 aftershocks with magnitude greater than 5.8.

                                                   WHOI earthquake seismologist Jeff McGuire has 
                                                      studied foreshocks extensively, a phenomenon 
                                                    in which a smaller quake seems to foreshadow 
                                                            a larger one. He and his colleagues have 
                                                                            developed a new suite of ocean 
                                                                     bottom seismometers (OBSs) capable 
                                                                 of accurately recording both foreshocks
                                                                         and mainshocks "A few percent of
                                                                            earthquakes will trigger an event 
                                                                          that is larger than the first event," 
                                                               he said. (Credit: Photo by Tom Kleindinst, 
                                                                  Woods Hole Oceanographic Institution)

"One of the areas hit by the tsunami, Sanriku, was hit by previous tsunamis, including a tsunami caused by a 1933 magnitude 8.1 quake that killed 3,000 people, as well as the tsunami from the 2010 magnitude 8.8 quake in Chile," he said.

He compared the current quake to the 1923 great Kanto earthquake of magnitude 7.9, which he said marked the beginning of modern seismology in Japan. "Although that was smaller than the current quake, it struck very close to Tokyo and Yokohama," Lin said. It caused more than 142,000 deaths and also caused a tsunami in the Sagami Bay with wave heights as high 20 to 39 feet in some areas.

McGuire and others have long been aware that a similar scenario could occur off the Pacific Northwest coast.

Led by McGuire, John Collins and Ken Peal, WHOI currently has ocean bottom seismometers deployed offshore of Vancouver Island to study the properties of the fault system there.

"Over the next five years, WHOI will be involved in the National Science Foundation's Cascadia Initiative," McGuire said. "This will be the first large-scale instrumentation of the fault offshore of Oregon and Washington that is capable of generating a magnitude 9 earthquake and tsunami."

In the meantime, Lin and his colleagues are heading to Christchurch, having just finished a very successful cruise of hydrothermal, geophysical, and geochemical sampling cruise of mid-ocean ridge segments "that nobody has studied before," he said.

Lin plans to survey the Christchurch earthquake zone and the widespread liquefaction before returning to WHOI on March 15.

After that, he will work with colleagues at the USGS National Earthquake Center in Menlo Park, Ca., to investigate both the Christchurch and Japan quakes