Guest post by Donald R. Prothero
On March 11, we mark the third anniversary of the huge Sendai earthquake and tsunami in Japan (officially known as the Tohoku quake of 2011, since it struck that region). It was the most powerful earthquake ever to hit Japan, and the fifth most powerful quake ever to occur since modern record keeping began in 1900. It started when the oceanic crust about 70 km (43 miles) to the east of Tohoku and 30 km below the surface thrust down into the subduction zone beneath Japan. This plate movement produced a quake with a moment magnitude of 9.0, and it caused the islands of Japan to shift 2.4 m (8 feet) east in a matter of seconds. The upward acceleration on the quake was almost 3 times the force of gravity, so many objects flew up in the air. It released almost twice as much energy as the Sumatran quake on Dec. 26, 2004, which killed a quarter of a million people. The energy released by the quake would have been enough to power Los Angeles for an entire year. The earthquake even shifted the earth’s axis and caused it to wobble as much as 10-25 cm (4-10 inches). It also generated low-frequency sound waves that could be detected by satellites.
The quake itself was frightening enough, but the real damage came from the tsunami, or seismic sea wave, that was produced when the ocean floor above the fault zone was pushed up 6-8 meters (20-25 feet) during the slippage between the plates. (Contrary to the popular myth, tsunami are not “tidal waves;” true “tidal waves” are caused by tides, not earthquakes). When this uplift occurs, it pushes water upward into waves with a very long wavelength, which move across entire oceans in a matter of hours. As the waves hit a coastline and “feel bottom,” however, they can no longer continue the orbital motion of water in the wave, and begin to break. This forms the gigantic wall of water that we have come to associate with a tsunami. The tallest tsunami waves were over 40 meters (133 feet) tall near Miyako, and in the Sendai area, the walls of water just kept flowing inland (unlike a normal storm wave or tidal wave) as much as 10 km (6 miles). As we witnessed from the staggering video footage, now available all over YouTube, the pulse of water just kept coming and coming, carrying dozens of cars as if they were toys and flattening buildings. Even more amazing to see are the aerial images on the internet of the wall of water moving across open farmland at an astounding rate, churning it up into a wall of mud.
Tide gauge showing the tsunami main pulse and the high water that followed
Although the shaking from the quake did a lot of damage, the tsunami was far more destructive as it plowed through already shattered buildings and structures and ripped them apart. Altogether, 127,290 buildings totally collapsed, at least 272,788 buildings ‘half collapsed,’ and another 747,989 buildings were damaged to some degree. The collapsing buildings and wall of water were virtually inescapable for most people living near the coastline. The death toll was reckoned at 15,884 people, with an additional 6,147 injured and 2,636 people who are still missing today and presumed dead in the debris or washed out to sea. So many people were dead that they could not have formal Buddhist funerals for them all, or cremate them properly. Instead, the bodies were thrown in mass graves to prevent the spread of disease.
Damaged train and debris carried by tsunami
The tsunami continued to spread eastward and southward across the Pacific, although most coastal towns had plenty of warning and were already preparing for the arrival of the first wave. Waves up to 2.4 meters (8 feet) tall hit coastal California and Oregon, causing $10 million in damage. In Curry County, Oregon, the destruction of the harbor (including 1,000 m, or 3,600 feet of dock space) cost over $7 million. Surges of over 1 m (over 3.3 feet) were reported on Vancouver Island, shutting down all boat transport and stranding people who needed to get to work. The waves hit in the Philippines, in Indonesia, and caused over $3 million in damage in Hawaii. The atolls of Midway Island were submerged, drowning 110,000 nesting seabirds who breed there. Even as far as Chile, the surge was 3 m (9.8 feet) high, and damaged over 200 houses. The tsunami even reached Antarctica, over 13,000 km (8100 miles) away, where it broke off icebergs on the Sulzberger Ice shelf. The biggest iceberg was 9.5 by 6.5 km (6 miles by 4 miles) in size, about the scale of Manhattan Island, and over 80 m (260 feet) thick. More than 125 square km (48 square miles) were broken off and released.
Spread of the tsunami energy across the Pacific
Most frightening off all the damage was the effects on the Fukushima Daiichi Nuclear Power Plant, which was already shut down for inspection and due to be decommissioned in a few months. Even though the seawalls withstood the force of the tsunami, the wall of water was enough to destroy the backup power system which keeps the reactors cool during the inspection. The shock waves caused cracks and leaks in the system, causing at least three level 7 meltdowns, and explosions of hydrogen gas in the outer containment buildings after the coolant system had failed. Radiation levels were one thousand times normal levels inside the plant, and at least eight times normal levels outside. Hundreds of thousands of people had to be evacuated, leaving a zone almost 80 km (50 miles) away from the plant that was cleared for fear of nuclear contamination. People have been monitoring the radiation levels in the three years since the quake and reactor breakdown. Although radioactive iodine has been detected in a number of places in Japan, the amount of leaking radiation spreading around the area was remarkably small, considering that this was the second worst nuclear accident in history after Chernobyl. The amounts of radioactive iodine and cesium is still being tracked but so far there are no apparent incidents of death or disease due to radioactive contamination.
In addition to radiation, other things are being tracked as well. Over the past three years, wreckage from Japan has appeared all over the Pacific. The most remarkable pieces of debris were chunks of docks torn away from the Japanese coast that have drifted as far as California (complete with their native Japanese marine tidepool creatures still attached and alive). A soccer ball from Japan was found in Alaska, and a Japanese motorcycle washed up in British Columbia.
All told, the losses ranged from $14 and 34 billion U.S. dollars. The Bank of Japan had to infuse 15 trillion yen ($183 billion US dollars) to stabilize the market. The World Bank estimated that the total cost of the disaster was $235 billion U.S. dollars, making it the most expensive disaster in world history. The Sendai quake taught us a lot about building safety, the best ways to cope with earthquakes and tsunamis, nuclear reactor safety, ocean currents, and even about plate tectonics. Let’s hope those hard-won lessons are not lost when the next great earthquake occurs.
Donald R. Prothero is a professor of geology at Occidental College and coeditor or author of many books, including Catastrophes! Earthquakes, Tsunamis, Tornadoes, and Other Earth-Shattering Disasters, Horns, Tusks, and Flippers: The Evolution of Hoofed Mammals, and The Evolution of Artiodactyls, all published by Johns Hopkins.
