The Aftermath: A Year After the Japanese Magnitude 9.0 Earthquake

The Aftermath: A Year After the Japanese Magnitude 9.0 Earthquake
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A year ago, event usc0001xgp of Magnitude of 9, occurred the Friday, March 11, 2011 at 02:46:24 PM at epicenter, 129 km (80 miles) East of Sendai, Honshu, Japan, at a 30 Km of depth, here (Google Maps) with a horizontal +/- 13.5 km error margin.

USGS summarizes the event that changed the history course of the country: “At least 15,703 people killed, 4,647 missing, 5,314 injured, 130,927 displaced and at least 332,395 buildings, 2,126 roads, 56 bridges and 26 railways destroyed or damaged by the earthquake and tsunami along the entire east coast of Honshu from Chiba to Aomori. The majority of casualties and damage occurred in Iwate, Miyagi and Fukushima from a Pacific-wide tsunami with a maximum runup height of 37.88 m at Miyako.

The total economic loss in Japan was estimated at 309 billion US dollars.”

One of the most striking videos of this event, is the one record by Yu Muroga is a Japanese driver. He was on his work shift when the earthquake occurred. Like most people of his area, he did not feel threatened by the Tsumani, as it was far enough from the coast. So he continued to drive and do his job. The HD camera mounted on the dashboard has not only captured the shock but also the moments that followed, where many drivers were stranded by the waters of the tsunami. The strength of the quake can clearly be seen during the first seconds of the video.

“The magnitude 9.0 Tohoku earthquake on March 11, 2011, which occurred near the northeast coast of Honshu, Japan, resulted from thrust faulting on or near the subduction zone plate boundary between the Pacific and North America plates. At the latitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a rate of 83 mm/yr, and begins its westward descent beneath Japan at the Japan Trench.

Modeling of the rupture of this earthquake indicates that the fault moved upwards of 30-40 m, and slipped over an area approximately 300 km long (along-strike) by 150 km wide (in the down-dip direction). Photo Credit USGS.

The beginning of the earthquake with the sound of the sudden movement of these tectonic plates movement was actually recorded. The following was recorded near the coastline of Japan between Fukushima Daiichi (the nuclear reactor site) and Tokyo. The initial blast of sound is the 9.0 mainshock. As the earth’s plates slipped dozens of meters into new positions, aftershocks occurred. They are indicated by “pop” noises immediately following the mainshock sound. The sound is impressive when accelerated by a factor 100. Plates adjustments and subsequent quakes will likely continue for years.

The Earthquake was not the main cause of the fatalities but rather the Tsunami that followed.  According to Georgia Tech University, “The 2011 Tohoku tsunami was Japan’s deadliest in more than 100 years.  Despite an extraordinary level of preparedness by the Japanese, the tsunami caused more than 90 percent of the almost 20,000 fatalities“. The inhabitants of the coastline hit by the Tsunami had an average of 10 minutes to seek shelter in the higher grounds of their locations. Many lives can be saved in 10 minutes if the appropriate infrastructures are available.

Georgia Tech University: “Georgia Tech Associate Professor Hermann Fritz and his research team are studying the impact of the tsunami on the Sanriku coast. Using eyewitness video and terrestrial laser scanners from atop the highest buildings that survived the tsunami, Fritz has mapped the tsunami’s height and flood zone to learn more about the flow of the devastating currents. Fritz’s measurements and observations could produce flooding forecasts that influence future evacuation plans and building designs, preventing loss of life and property damage in Japan and in other areas of the world susceptible to tsunamis.

Fritz led a reconnaissance team surveying the impact of the tsunami on a fishing town in Kesennuma Bay, where 1,500 people perished. The bay has been hit by historic tsunamis in 1896, 1933, 1960 and 2010—making it the most vulnerable in Japan to both near- and far-field tsunamis. The coastal structures and other mitigation measures on the coast were designed based on conservative, historic high-water marks, rather than probable maximum tsunamis.

From two atop vertical evacuation buildings where eyewitnesses gathered during the tsunami, Fritz and his team used lasers to scan the port and bay entrance, creating a three-dimensional, topographic model of the flood zone.

Using this data, they reconstructed eyewitness videos to determine the varying heights and flow velocities of the tsunami. They determined that the tsunami reached a maximum height of 9 meters, followed by outflow currents of 11 meters per second less than 10 minutes later – a speed which Fritz says is impossible to survive or navigate by vessels.

“What we can learn from the hydrograph is confirmation that the water goes out first, drawing down to more than negative 3 meters on the landward side of the trench, which can make vessels hit ground inside harbors,” Fritz said. “During the subsequent arrival of the main tsunami wave, the water rushing back in changed the water level by 40 feet, engulfing the entire city in 12 minutes.”

Understanding tsunami impacts will help prepare for future disasters—whether its designing buildings high enough to serve as vertical evacuation points or sea walls and breakwaters strong enough to control the flow of water.

Along with such mitigation measures, Fritz says educating people about tsunamis is key.

“Japan was probably the best prepared for a tsunami,” Fritz said. “Indonesia, on the other hand, had no knowledge of tsunamis and it caught people by surprise in 2004. The outcomes of the tsunamis were very different—200,000 killed versus 20,000 killed. That shows educational awareness and preparedness and civil defense mechanisms can work to reduce the death toll. People need to be tsunami-aware.”

Sources: USGS / Georgia Tech – Videos Selected by Cap Falcon

Photo Credits: Hanami #2 (final C.A.F.E. version) By cktse / FlickR

我々は、この恐ろしい地震で亡くなった人の冥福を祈る, Cap Falcon