Geologists suspect that today’s quake was actually an aftershock of a much weaker magnitude-7.2 quake on 9 March. They warn that seismic stress has not yet relaxed in some particularly vulnerable parts of Japan, including the Tokyo region, 400 kilometres south of today’s epicentre.
“Although certainly very big, today’s quake was not totally unexpected,” says John McCloskey, a geophysicist at the University of Ulster in Coleraine, UK. “Technically, it was in fact an aftershock of the weaker quake earlier in the week — even though it may sound odd that an aftershock can be stronger than the main shock.”
“The previous quake, although much smaller, significantly increased stress in the fraction of the fault zone that ruptured today,” says McCloskey.
The sequence of quakes has probably also affected the stress field further south along the fault zone, critically increasing the earthquake risk in the Tokyo region, he says.
“There is a strong interaction of quakes along a subduction zone, and we can certainly expect a number of major aftershocks in the next weeks,” he says. “Some may be as large as, or even stronger than, the quake that last month devastated Christchurch in New Zealand. And chances are that another very large shock could occur to the south near Tokyo.”
Today’s quake seems to have abruptly displaced the seafloor off Japan by a few metres, which caused the tsunami.
According to local reports, the tsunami reached up to 10 metres in height when it hit Japan’s Sanriku coast barely 30 minutes after the quake. Along flat coasts, the tsunami propagated hundreds of meters inland, sweeping away homes, cars and roads. Sendai airport was completely flooded. The number of people killed in the tsunami is as yet unclear, but reports suggest it could be several hundred.
LOS ANGELES — California is closely watching the crisis at a Japanese nuclear plant, but officials downplayed the threat that a radioactive cloud blown across the Pacific could pose for the US West Coast.
While radioactivity could reach the United States from the quake-hit Fukushima plant, the levels would not be high enough to cause major health problems, said the Nuclear Regulatory Commission (NRC).
Some experts disagreed, notably pointing to the west-east jet stream, but NRC — which was asked by Japan on Monday to send nuclear experts to deal with the crisis — said even the Pacific island state of Hawaii faced little risk.
“Right now it’s quite possible that there could be some radiation floating over the United States. But we don’t think that it would be particularly harmful… even in a worst case scenario,” spokesman David McIntyre told AFP.
The radioactive cloud of steam and gases blown into the air by the explosions at the reactors in the Fukushima nuclear plant are unlikely to pose a major health risk, radiation experts said yesterday – although any future explosion could change the situation.
Relief agencies said the main threat for those who had survived near- drowning in the tsunami would be pneumonia, caused by fluid retained in the lung.
Thousands of corpses litter coastal towns but outbreaks of diseases such as cholera are considered a low risk in a developed country.
We have been sitting on a powder keg all the time.
What is this information/institution for if we do not act ?
Probably US might be next,taking into consideration Andrea’s faukt in California.
The Plate is very unstable.
A screen grab shows a tsunami simulation with a prediction of possible spots that could be hit by giant waves after the Japan earthquake. (Picture: EPA)
Extraordinary map showing energy of Tsunami as it crosses the Pacific from Japan after the earthquake. (Picture: US TSUNAMI WARNING CENTRE)
Radiation levels have risen above the safety limit around Tokyo Electric Power Co’s (TEPCO) nuclear plant hit by a massive earthquake and the company has informed the government of an “emergency situation,” Kyodo agency reported on Sunday.
The exterior of reactor No. 3 at Fukushima Daiichi nuclear plant is seen in this still image taken from undated file video footage. Japan battled to contain a radiation leak at an earthquake-crippled nuclear plant on March 13, 2011, but faced a fresh threat with the failure of the cooling system in a second reactor. Operator TEPCO said it was preparing to release some steam to relieve pressure in the No.3 reactor at the plant 240 km (150 miles) north of Tokyo — which would release a small amount of radiation — following an explosion and leak on Saturday in the facility's No. 1 reactor. Credit: Reuters/NHK via Reuters TV
It did not mean an immediate threat to human health, the company said.
The company said earlier that it had started releasing steam from a reactor at the plant. A similar rise in radiation levels occurred after the company released radioactive steam from another reactor to let go of pressure. Then again the company was obliged to inform the government of an “emergency situation.”
The highest recommended limit for radiation exposures is for astronauts-25,000 millirems per Space Shuttle mission, principally from cosmic rays. This amount is beyond the average 300+ millirems of natural sources of radiation and any medical radiation a person has received.
25,000 millirems per year level was the federal occupational limit during World War II and until about 1950 for radiation workers and soldiers exposed to radiation. The occupational limit became 15,000 millirems per year around 1950. In 1957, the occupational limit was lowered to a maximum of 5,000 millirems per year.
Average Natural Background: 300 Millirems
The average exposure in the United States, from natural sources of radiation (mostly cosmic radiation and radon), is 300 millirems per year at sea level. Radiation exposure is slightly higher at higher elevations-thus the exposure in Denver averages 400 millirems per year.
(A milliRem is 1/1000th of a Rem. According to McGraw-Hill’s Dictionary of Scientific and Technical Terms, a Rem is a unit of ionizing radiation equal to the amount that produces the same damage to humans as one roentgen of high-voltage x-rays. The name is derived from “Roentgen equivalent man.” Wilhelm Roentgen discovered ionizing radiation in 1895 at about the same time that Pierre and Marie Curie discovered radium.)
All of these limits are for the amount of radiation exposure in addition to background radiation and medical radiation.
Adult: 5,000 Millirems
The current federal occupational limit of exposure per year for an adult (the limit for a worker using radiation) is “as low as reasonably achievable; however, not to exceed 5,000 millirems” above the 300+ millirems of natural sources of radiation and any medical radiation. Radiation workers wear badges made of photographic film which indicate the exposure to radiation. Readings typically are taken monthly. A federal advisory committee recommends that the lifetime exposure be limited to a person’s age multiplied by 1,000 millirems (example: for a 65-year-old person, 65,000 millirems).
Minor: 500 Millirems
The maximum permissible exposure for a person under 18 working with radiation is one-tenth the adult limit or not to exceed 500 millirems per year above the 300+ millirems of natural sources, plus medical radiation. This was established in 1957 and reviewed as recently as 1990.
Fetus: 500 Millirems Or 50 Per Month (New Rule Jan. 1, 1994)
New federal regulations went into effect New Year’s Day, establishing for the first time an exposure limit for the embryo or fetus of a pregnant woman exposed to radiation at work. The limit for the gestation period is 500 millirems, with a recommendation that the exposure of a fetus be no more than 50 millirems per month.
Weight Variables
Like alcohol intoxication levels, levels of exposure to radioactivity (due to radioactivity deposited in the body) depend on a person’s weight. A diagnostic tracer of one microcurie of radioactive calcium 45, given orally, would result in an exposure of 3.7 millirems for a 100-pound person, and half of that, 1.85 millirems, for a 200-pound person.
Therapeutic radiation treatment that is delivered by administering radioactive material via the mouth or by injection usually results in high, very localized doses to a small part of the body, which absorbs most of the radioactivity. The radioactivity concentrates and remains in the target organ (for example, the thyroid) for a longer period of time than does the radioactivity that is distributed to the rest of the body. The radiation exposure for other parts of the body is a function of the amount of radioactivity per pound and the time the radioactivity is present in the tissue.
This figure illustrates the relative abilities of three different types of ionizing radiation to penetrate solid matter. Alpha particles (α) are stopped by a sheet of paper while beta particles (β) are stopped by an aluminium plate. Gamma radiation (γ) is dampened when it penetrates matter.
In physics, radiation describes a process in which energetic particles or waves travel through a medium or space. There are two distinct types of radiation; ionizingand non-ionizing. The word radiation is commonly used in reference to ionizing radiation only (i.e., having sufficient energy to ionize an atom), but it may also refer to non-ionizing radiation (e.g., radio waves or visible light). The energy radiates (i.e., travels outward in straight lines in all directions) from its source. This geometry naturally leads to a system of measurements and physical units that are equally applicable to all types of radiation. Both ionizing and non-ionizing radiation can be harmful to organisms and can result in changes to the natural environment.Radiation hormesis is the theory that low doses of radiation can be beneficial toorganisms.
-(Wikipedia)
Radiation Effects.
Certain body parts are more specifically affected by exposure to different types of radiation sources. Several factors are involved in determining the potential health effects of exposure to radiation. These include:
The size of the dose (amount of energy deposited in the body)
The ability of the radiation to harm human tissue
Which organs are affected
The most important factor is the amount of the dose – the amount of energy actually deposited in your body. The more energy absorbed by cells, the greater the biological damage. Health physicists refer to the amount of energy absorbed by the body as the radiation dose. The absorbed dose, the amount of energy absorbed per gram of body tissue, is usually measured in units called rads. Another unit of radation is the rem, or roentgen equivalent in man. To convert rads to rems, the number of rads is multiplied by a number that reflects the potential for damage caused by a type of radiation. For beta, gamma and X-ray radiation, this number is generally one. For some neutrons, protons, or alpha particles, the number is twenty.
Hair
The losing of hair quickly and in clumps occurs with radiation exposure at 200 rems or higher.
Brain
Since brain cells do not reproduce, they won’t be damaged directly unless the exposure is 5,000 rems or greater. Like the heart, radiation kills nerve cells and small blood vessels, and can cause seizures and immediate death.
Thyroid
The certain body parts are more specifically affected by exposure to different types of radiation sources. The thyroid gland is susceptible to radioactive iodine. In sufficient amounts, radioactive iodine can destroy all or part of the thyroid. By taking potassium iodide can reduce the effects of exposure.
Dose-rem
Effects
5-20
Possible late effects; possible chromosomal damage.
20-100
Temporary reduction in white blood cells.
100-200
Mild radiation sickness within a few hours: vomiting, diarrhea, fatigue; reduction in resistance to infection.
200-300
Serious radiation sickness effects as in 100-200 rem and hemorrhage; exposure is a Lethal Dose to 10-35% of the population after 30 days (LD 10-35/30).
300-400
Serious radiation sickness; also marrow and intestine destruction; LD 50-70/30.
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