Japan’s Oceanic Disaster

These trenches are located in the deepest parts of the ocean and are formed by the movement of the Eurasian, Pacific, Philippines and North American plates. The total spatial dimension of Japan is 3,74,744 sq km and it has a population of approximately 127,408,889. Around 3,232 cities, towns, villages etc are located in Japan and out of these about 500 cities and towns are significant from the demographic, physiographical, industrial and technological point of view. Japan’s seismic micro-zonation is very advance in the world and rapidly changes its methodology because of advance studies and its relevant technologies apart from behavior of seismology-tectonic conditions prevails in the main islands. A total of 6,832,000 people are living in these 500 cities situated in a very high seismic zone which may see an earthquake of VIII -IX magnitude. Likewise, 27.53% of population is living in a seismic zone that may receive a magnitude VII earthquake, 16.6%of the population in probable VI magnitude, 6.04% population in probable V, 14.38% in IV, 27.22% in III and 4.51% in magnitude II.

The Tohoku Earthquake of March 11, 2011 was the fourth strongest in the world since 1900. In terms of strength, the US Geological Survey placed the magnitude 9.0 earthquake just behind the 2004 earthquake off the coast of Sumatra, Indonesia. This occurred on the eastern coast of Honshu island with a moment magnitude of 9.0 and is the seventh strongest quake recorded on this planet. Actually, for Japan, it was an unprecedented tremor in terms of size and the severe secondary risk while it carried of tsunami. The great Kanto earthquake with a magnitude of 8.4 which struck Japan in September 1923 was the largest earthquake in the recent history of Japan in terms of fatalities of more than 142,000 people. It may be stated that most of Japan’s seismic activities are taking place on the east coast of Honshu island and innumerable earthquakes of different magnitudes have struck the area. Though most of the earthquake’s epicenters are concentrated on the east coast of Honshu yet some significant earthquakes have also rocked all the main four Islands of Japan which left behind a lot of structural damages and killed many people. The southern part of Japan is also severely prone to earthquakes keeping in view the clusters of epicenters which developed in 1944 and 1946.

The Great Eastern Japan Earthquake of March ‘11 was a significant one from various aspects of seismology. The epicentre was marked on 38.322°N, 142.369°E near the east coast of Honshu with a focus depth of 32 km which gave rise to moment magnitude of 9.0 Mw . The epicentral distance was measured from 129 km east of Sendai, 177 km east of Yamagata, 177 km ENE of Fukushima, and 373 km NE of Tokyo. However, around 50 million people had perceived vigorous ’shaking’ at the main Honshu Island. The quake was so strong that the earth shook for around 6 minutes. Moreover, soon after the giant March 11 earthquake, a series of powerful quakes ranging from 5.8 Mw to 7.1 struck the main island Honshu within half-an-hour and all the epicenters were located at a close distance to the great quakes epicenter and had similar depth of focuses. In the seismological history of Japan, such violent aftershocks had never occurred. In this earthquake there was an established methodology of fore shocks and aftershocks of a giant earthquake. The earthquake had been preceded by a series of large fore shocks over the previous two days, beginning on March 9 with an M 7.2 event approximately 25 miles from the March 11 earthquake, and continuing with three earthquakes greater than M 6 on the same day.
The giant quake was extremely destructive which triggered tsunami waves up to 38 meters high. In Fukushima prefecture , it triggered waves up to 15 meters high and entered the valleys and plains about 10 km from the sea coastal line. Tsunami hit the important cities of north-eastern Japan such as Miyako , Fukushima, Sendai etc., 25 minutes after the tremor struck at a distance between 129 km to 177 km from the ocean. Walls of water whisked away houses and cars as terrified residents fled away the coast. A ship carrying more than 100 people was reportedly swept away by the tsunami. At least 400 square kilometers of land was flooded by the tsunami, an area equivalent to 20 per cent of the area of Tokyo. The tsunami reached a maximum distance of 6 km inland. A tsunami, at least 7.3 meters high was observed in Soma and a 14 meter giant at Fukushima Prefecture. A study by the researchers of Tohoku University found that the tsunami reached a height of 10 meters in Sendai’s Wakabayashi Ward. An analysis by experts at the Earthquake Research Institute of the University of Tokyo found that the tsunami hit land as soon as 10 minutes after the earthquake struck. As Japan has a very advanced warning system and emergency operation management hence, the Japanese Meteorological Agency issued tsunami warnings 3 minutes after the quake. The agency urged the Japanese people on the east coast of Honshu to evacuate the low-lying coastal areas immediately and to rush to higher ground as the quake could generate tsunami waves up to 6 meters high from the mean sea level at Miyagi and Fukushima prefectures.

Accurate tsunami warning is a very tough simulation exercise because of the redundancy of seismic and hydrodynamic data transmitted by accelerograph and Tsunameter. More interestingly, the exact size and shape of fault /thrust developed by an earthquake under the oceanic floor cannot be estimated due to the complex characteristics of bathymetric formation. Hence, it is a tough exercise to estimate the exact displacement of water due to the rupturing of a fault beneath the ocean. Moreover, various trenches of Japan are not at the same altitude below the mean sea level and vary from 4 to 12 km beneath the sea. Yet, the Japan Meteorological Agency issued more or less accurate urgent warning. Also NOAA’s Pacific Tsunami Warning Center issued the warnings for the entire Pacific coastlines area including the Hawaii island. The earthquake-related Tsunami warnings are dependent primarily on mathematical calculations of seismic information and coastal tide gauge measurements. It is a highly valuable data but indirect and real interpretation is very difficult due to the complex Tsunameter network placed on sub sea, ocean floor, buoyant and land which transmits signal to the meteorological satellites. Even tide gauges do not survive the impact of a real time tsunami resulting in loss of transmission of data. Sometimes a tsunami can be detected only after it strikes the coast like during the Southeast Asia tsunami in spite of having availability of the Global Tsunameter network in the Indian Ocean. It is very difficult to find out the speed of Tsunami waves, locating the crest and the trough of the waves and its wavelength, height, amplitude, and velocity with which the waves would strike the coast line. Generally, the crest of the tsunami wave generate high run up when it hits the coast first.
In general, velocity of a normal ocean waves are about 90 km/hr but it reaches up to 950 km/hr which is equivalent to the speed of the jet fighter planes, and thus move much more rapidly across ocean basins. The velocity of any wave is equal to the wavelength divided by the wave period. In the case of the March 11 tsunami there was a big wavelength of Tsunami waves and 25 minutes were required to reach the coast of the Fukushima Prefecture located 177 km away from the epicenter. It can be assumed that higher the wavelength of tsunami waves more time is needed to reach the coast which is dangerous for the coastline people if the crest of the waves strike the coast first.

Unfortunately, Japan suffered a lot after losing about 14,500 energetic people and nearly 12,000 people are still missing from the Fukushima and Miyagi prefectures. Out of 12000 missing people, it may be expected that most of them were carried off to the interior of the ocean by the speedy receding waves. This is really unfortunate for Japan as she is very advanced in efficient disaster management system and is putting a latest risk management in place. Japan is the world’s topmost country in mitigating hydro-meterological and geological natural disasters. She is technologically high in on scene management and response mechanism. From the occurrence of disastrous tsunami it may be assumed that Japan was not fully prepared for the disastrous tsunami . Of course, there was a 10 metre dyke wall at Fukushima to prevent the nuclear plant from tsunami but it could not save the nuclear plant as the wave rose to a height of 14 metres at Fukushima Prefecture. As a result tsunami waves entered the nuclear plant and damaged reactor no 2 and 4 as the cooling system was disrupted due to power failure at the plant. The reactor came crashing down with a blast as soon as the nuclear fuel melted due to increasing high temperatures.

This recent oceanic disaster at Japan has revealed the lacking of preparedness to fight with the tsunami. Still it may be remembered here that even though the size of the tsunami was massive the damage it caused was minor if we consider what disaster a similar tsunami may have caused across other countries in the world. Japan is much advanced in earthquake resistant and earthquake proof technologies and is the best in the world. This was proved once again from this quake because neither a single building collapsed directly due to shaking at 9 moment magnitude just 123 km away from Miyagi city. It was quite unbelievable that structures were standing even after there was a continuous shaking for about 6 minutes when the surface magnitude became abruptly high due to the size of the earthquake. But in contrast, the tsunami took a disastrous form as it washed away every physical and navigation structure which came in its way.

Japan’s technology in disaster management is the best in the world and it is very strong in the field of disaster risk reduction because of implementation of updated technology. Each of the phases of disaster risk reduction like prevention, mitigation, preparedness and response are very strong and are efficiently managed. The Government is well prepared to face any disaster and the Japanese people are well aware of this. The attitude of the people during the crisis was really appreciable as they showed a positive attitude to the government response system, with their calmness and without showing any signs of panic. People did not create any law–and-order situation for seeking any help or relief materials and had full faith on the government for an efficient response. It is unbelievable that lakhs of people were evacuated from radius of 20 km of the Fukushima Nuclear Plant so smoothly and efficient temporary relief and rehabilitation on an open space and recreational hall was given to those people who had lost their homes and had to be evacuated immediately to save them from nuclear radiation. Trauma counselling is being given along with the best treatment in the earthquake-proof hospitals very efficiently to thousands of injured persons.

The search & rescue operation system is also very advanced in Japan. These operations were carried out by well equipped task forces and strike teams along with aerial operations. It is interesting to note that not a single developed country offered assistance by human or other resources as the country is much ahead of others in terms of machinery and technical equipment. But the management took much time to manage the nuclear crisis as they were hoping that the nuclear reactors could be salvaged. Radiation was found to be very high in the air but it was blown away towards the Pacific Ocean and that is one of the reasons why Japan took so much time to come out of this tragedy.

About the Author

Author is a Geologist and Remote Sensing & GIS Scientist and is  interested to carry out the work in the field of Municipal GIS & Urban Planning and Disaster Risk Management.

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