Magnitude 6.9 Earthquake Shakes Japan

On Tuesday Nov. 22, a magnitude 6.9 earthquake hit northern Japan. The quake was originally recorded as having a magnitude of 7.3, but has since been brought down to 6.9 by the United States Geological Survey. The Japan Meteorological Agency has stated that the earthquake was positioned off the coast of Fukushima at a depth of 6 miles.

A small tsunami followed suit.

Japanese public broadcaster NHK reported that a wave of up to 4.5 feet high was seen at the city of Sendai, 45 miles north of Fukushima.

No fatalities occurred in the quake, although 15 were injured.

NHK stated that, “a woman in her 80s in Kashiwa City in [the] Chiba Prefecture broke her leg when she lost her footing and fell down stairs in her house. A woman in her 70s in Yabuki Town in [the] Fukushima Prefecture was injured when a cupboard toppled over. [And,] 13 other people were also injured in Tokyo and Fukushima, Miyagi and Chiba Prefectures.”

In response to the event, Japanese Prime Minister Shinzo Abe stated that the Japanese government planned to put their best effort into emergency response. Abe said, “We will announce any information regarding tsunami or evacuation swiftly, and will quickly gather information regarding any damages, and will put in our best effort in responding to emergencies. We will also work together with local municipalities, and become united as a government to ensure safety and respond to disasters the best we can.”

This most recent earthquake, called for a reflection on the unembellished natural disaster that took place five years prior, also in Fukushima, that involved a massive earthquake, multiple tsunamis, and a nuclear disaster. The travesty of March 11, 2011 was so notorious that it has gone down in history as the Great Sendai Earthquake and Great Tōhoku Earthquake.

According to CNN, the Great Sendai Earthquake of 9.0 magnitude was one of the worst ever to hit Japan, killing more than 20,000 people and causing tsunamis of up to 40 feet that swamped the Fukushima Daiichi nuclear power plant, thus triggering a nuclear meltdown, the worst since Chernobyl.

Japan is susceptible to such devastating earthquakes due to its location in the Pacific Ring of Fire, a string of volcanoes and sites of seismic activity around the edges of the Pacific Ocean. Because of this, Japan accounts for 20 percent of the world’s earthquakes with magnitudes of 6 or more.

Since the earthquake in 2011, Japan has taken great safety precautions, ensuring that emergency systems be updated to spread warnings more quickly.

 

Physically Explaining Japan’s Natural Disaster

Amidst a rush of news stories covering the recent triple-disaster in Japan, it is often hard to fully understand all of what has happened merely from reading about it in popular publications. Three physics faculty members held a special forum to discuss the recent disaster in Japan, and specifically the ongoing nuclear crisis at the Fukushima plant.

Assistant Professor of Physics Josh Grossman explained what happens to the Earth and water during an earthquake and tsunami. All earthquakes are caused by pressure buildup as plates of the Earth’s crust push against each other and become stuck. An earthquake is what happens when these plates suddenly become unstuck and move around. On March 11, that compressed energy was violently released in the form of a magnitude 9.0 earthquake, moving Japan and North America eight feet closer to each other.

“A lot of the time it’s hard to wrap our heads around the way a tsunami behaves,” explained Grossman. A tsunami isn’t just a giant wave that heads for shore. It starts out as a barely-perceptible bulge in the ocean, though underneath a shock wave of water is traveling at hundreds of miles an hour, almost as fast as a jet plane. As that shock wave reaches the shore, the sea floor bottom compresses the shock wave into those towering waves that we all think of as a tsunami.

“When the quake hits, the power plants shut down, as a basic safety measure,” explained Assistant Professor of Physics Erin De Pree in her talk about the responses to the disaster. “Then the tsunami hit. This was a problem.”

The tsunami knocked out Fukushima’s backup generators. Four hours after the earthquake and tsunami had struck,  the plant was forced to switch to battery power. The most important thing that electricity did at the power plant was keep chambers filled with waste, called spent fuel pools, properly cooled. After the backup generators were lost, all the energy from the batteries was spent keeping the spent fuel pools from overheating.

“It was scarier than Three Mile Island, because the power shut off in the control room to conserve electricity for cooling the reactor,” said De Pree. The control room was dark, and operators could not read any direct readouts from sensors in the reactor. After less than a day, these backup batteries ran out of power and there was nothing to keep the spent fuel from overheating except the pools of water that surrounded the spend fuel — which began to boil. Since then, all efforts that the Japanese government and Tokyo Electric have made have involved keeping these spent fuel pools from boiling away all the water and risking a nuclear meltdown.

The Fukushima crisis was not the same as the crises at Three Mile Island or Chernobyl. “This is the first time spent fuel pools have been newsworthy since the 1950s.”

Why use nuclear energy at all then, if it’s so dangerous? “If you use one gram of Uranium-235 (U-235) you have 1 megawatt for a day,” said Professor of Physics Katsunori Mita. For the same amount of energy in coal, explained Mita, you would need 2.6 pounds, over a thousand times more in weight. Plus, using U-235, the spent fuel will be converted into Plutonium 239 – which is usable as a nuclear power source. “An amazing thing about nuclear energy [is] you can make more fuel than it consumes,” said Mita.

On top of that, nuclear energy is normally not so dangerous. “When the splitting of the nucleus occurs, enormous amounts of power are released, [but] the reactor cannot become a bomb. That’s impossible. There is not enough uranium,” concluded Mita.