Tuesday, May 24 2011 Japan Times
|Duck and cover: Children at Isatomae Elementary School in Minamisanriku, Miyagi Prefecture, hide under their desks during a disaster drill May 12. KYODO PHOTO|
Many claim the magnitude 9.0 earthquake and tsunami of March 11 exceeded all expectations.
Breakwaters and seawalls that were built along the coastal areas of the Tohoku region were destroyed by the waves, unable to prevent them from swallowing up houses, factories and schools.
Thousands of people didn’t escape despite the tsunami warning system.
However, because Japan is so prone to seismological disturbances, people have long taken preventive measures against earthquake and tsunami.
Following are basic questions and answers on how the nation has prepared for the disasters:
Is there any way to know there will be an earthquake in advance?
Yes. The earthquake early warning system operated by the Meteorological Agency provides advance warning of earthquakes.
According to the agency, the nationwide system is unique to Japan. But it only gives people seconds, not days, to prepare.
When an earthquake hits, two kinds of waves travel underground, first the P-waves and then the S-waves. When the agency detects P-waves, a warning is sent immediately, before the S-waves, which people actually feel, arrive.
People can receive the warnings on mobile phones operated by NTT DoCoMo Inc., Softbank Mobile Corp. and KDDI’s au, or through TV or radio broadcasts.
But according to the Meteorological Agency, there is as little as only 10 seconds between the warning and when the tremors arrive. Close to the epicenter, the quake arrives faster than the warning.
The Meteorological Agency updates its technology to improve the system every time it encounters problems. For example, the system didn’t function properly after the March 11 quake because big quakes occurred too frequently. The agency is now working on solving this issue, according to its Seismological and Volcanological Department.
What about tsunami?
The Meteorological Agency gives a tsunami warning within three minutes of when a quake begins. The warning includes information on height, estimated time of arrival and endangered areas.
Because the warning needs to be sent out quickly, the agency has developed a system in which it runs a simulation based on accumulated data and active faults that can trigger tsunami after the quake strikes, instead of calculating wave height and arrival time after a quake.
How can tsunami be prevented from inundating land?
About 9,400 km of the nation’s coastline, or about 27 percent of the total, are equipped with shore protection such as breakwaters and seawalls. Breakwaters are built in the sea to protect the shore from big waves, while seawalls are large concrete structures designed to keep them from flowing over the land.
How tall the seawalls are built varies depending on the location. At 15.5 meters, one of the tallest protects the village of Fudai, Iwate Prefecture.
But only 37 percent of the protective installations can endure significant earthquakes, according to a 2010 report by the Land, Infrastructure, Transport and Tourism Ministry, meaning the majority of Japan’s coastline lacks decent protection from quakes and tsunami.
Did breakwaters and seawalls help stop the tsunami generated by the Great East Japan Earthquake?
Not really. The 2.4-km-long seawall in Miyako, Iwate Prefecture, one of the longest in Japan, was destroyed by the tsunami of March 11. The seawall stood 10 meters high, but the tsunami that struck Miyako simply engulfed it.
Even the deepest breakwater in the world, located in Kamaishi, Iwate Prefecture, was destroyed by tsunami. The base was built 63 meters deep, the top stood 6 meters above the sea’s surface, and the total length was 2 km. It was built in 2009 to protect the town from tsunami measuring 5.6 meters high, while the tsunami of March 11 was 10.8 meters high.
However, the breakwater in Kamaishi delayed the tsunami from sweeping through the residential area for six minutes, according to the land ministry.
The 15.5-meter-high seawall in Fudai, built in 1967, also provided some protection. All of the villagers were later reported safe, apart from one person who went missing. Originally, the height of the seawall was set at 10 meters, but former village chief Kotoku Wamura fought to make it higher because he believed in the lessons of history, saying a 15-meter-high tsunami struck the village in 1896.
An elementary school and a village just inside the seawall remained intact despite huge damage to neighboring towns and cities.
Are there any regulations to make buildings and houses more quake-resistant?
Yes. The latest regulations on buildings were implemented in 1981 when the Building Standard Act was revised after a major earthquake off Miyagi Prefecture in 1978. The regulations stipulate that buildings must be constructed to survive earthquakes with a seismic intensity of 6 or higher.
The standard has been upgraded every time a major earthquake strikes.
The first standard for buildings, set forth in 1920, was revised after the magnitude 7.9 Great Kanto Earthquake of 1923. The Building Standard Act was established in 1950 after a magnitude 7.1 quake hit Fukui Prefecture in 1948, and was revised in 1971 after a major tembor with a magnitude of 7.9 hit Hokkaido’s Tokachi region in 1968.
In Tokyo, the metropolitan government aims to ensure that 90 percent of all buildings meet the standard for quake resistance by fiscal 2015, up from about 75 percent today.
Recently, seismic isolation systems are being designed into some buildings. Springlike units are placed at the base of the building, isolating it from the ground. According to the Japan Society of Seismic Isolation, the system reduces the speed at which a building shakes during a quake.
What kinds of emergency drills are held?
Many institutions, including schools and office buildings, conduct mandatory fire drills each year. Exercises held by communities and schools on Sept. 1, the day of the Great Kanto Earthquake, are focused on quakes.
Some schools in highly seismic areas, including in the Tohoku region, give weekly classes on disaster preparation. Students from different schools even compete with each other at the Bosai Koshien, or national disaster prevention competition, held every year by the Mainichi Shimbun.
Some organizations hold drill s to let people practice walking home from their offices because most public transportation will stop after a big earthquake.
Local governments within 10 km of nuclear plants across Japan conduct a special kind of drill, according to the Nuclear and Industrial Safety Agency. Usually, residents take part in the drill while the local government prepares iodine tablets.
Kyoto Prefecture, which is close to the Takahama nuclear power plant in Fukui Prefecture, decided to expand the area for the drills to 20 km from the facility after the crisis at the Fukushima No. 1 nuclear power plant showed that a 10-km buffer can be inadequate.
How can someone find out if their neighborhood is likely to be affected by quakes or tsunami?
They can check a hazard map created by the land ministry and local governments. There are also maps that estimate liquefaction.
For Tokyo, a map showing which areas are prone to liquefaction is available at the website of the metropolitan government’s civil engineering division.