An earthquake of magnitude 7.8 with its epicenter close to the city destroyed most of Tokyo and burned down what was left. Death toll was 150,000 and an additional million were left homeless.
On the first day of September 1923, Tokyo was hit with a powerful 7.8 strength earthquake. It was centered south of Tokyo, at that time a city of 2.3 million, the world’s fifth largest. Many aftershocks followed. As had happened with the San Francisco earthquake, seventeen years earlier, the main destruction came from outbreaks of fire. Open cooking utensils spilled their coals on to wooden kitchen floors. When flames appeared there was no water available to quench them as the piping had been severed when the earth shook. Thousands of fires soon sprang up, rising gradually to a firestorm as they easily jumped over the narrow streets to ignite the next row of wooden homes. When the fires finally died down and conditions in Tokyo and the areas nearby were assessed, about 150,000 had died and a million were left homeless.
Tokyo, the city known as Edo in earlier centuries, became the administrative capital of the country about four hundred years ago under the control of the Tokugawa family who extended the city’s territory by reclaiming land at the mouth of the Sumida River. Unconsolidated ground, that is to say the filled land on which new areas of the city were built, is a dangerous place when an earthquake strikes as was seen during the 1906 San Francisco earthquake. The shaking transforms such land, turning it into a kind of jelly that cannot support the buildings standing on it.
In 1868, Tokyo came under a new form of government, one that brought the Emperor from Kyoto to Tokyo to take his place as ruler of the whole country. Un- der this new regime the city flourished, bringing it to its high population. The filled land, however, remained as it had been in earlier years, so liquefaction and destruction of many buildings in this part of the city became additional features of the earthquake.
Rebuilding the Kanto area west and south of Tokyo was a major undertaking. To compound the problem, the Prime Minister of Japan had died suddenly and his successor had not yet taken office, nor identified his cabinet, so various members of the previous government had to take responsibility for the restoration work. The first thing they did was to declare martial law. It was the only way to cope with the widespread destruction and the raging fires. Fortunately, there were many individuals and agencies, both locally and in many other countries, able and ready to help.
Reconstruction went ahead with remarkable speed, perhaps because Japan is so used to earthquakes that it reacts with predictable speed when a big one hits. Streets were laid out in the same patterns they held before the earthquake, often semi-circular and always narrow in order to provide space for the hundreds of thousands who needed housing. Such an arrangement was bad from the point of view of future earthquakes or outbreaks of fire but the damage done was so great that the needs of people outweighed the advantages of making the city better prepared for the next earthquake.
The Philippine Plate moved about ten feet in a northwestward direction as the fault slippage occurred, and numerous ground fissures, land uplift, and areas of subsistence were seen. Parts of Sagami Bay were uplifted twenty-five feet and then slowly, over a four-week period, sank back to within five feet of their original elevation. At the same time, parts of Sagami Bay subsided by more than six hundred feet. This amount of subsidence could not be explained on the basis of the fault slippage.
Following subsequent examination of the sea floor geologists concluded that the earthquake had triggered mudflows and enormous quantities of sedimentary material had been carried out of the bay into deeper water. It was also concluded that the shaking from the earthquake had compacted much of the unconsolidated material on the sea floor. The great depths of six hundred feet could have been formed in such ways. A few minutes after the earthquake occurred, a tsunami that reached heights of forty feet swept across the Boso Peninsula on the east side of Tokyo Bay, causing a large number of deaths.
The earthquake was directly responsible for many of the deaths in and around Tokyo as buildings collapsed on people. However, it was fire that killed the largest number of people. Everything happened at noon when midday meals were being prepared over open charcoal braziers. As thousands of these hibachis were knocked over on to wooden floors a mass of fires broke out and there was no water to extinguish them because the city’s water mains had been severed.
People poured out on to the streets for safety, taking as much of their personal possessions as they could carry, but safety eluded them. The mushrooming fires, aided by a strong wind, turned into a firestorm and streets became deadly traps. On the east bank of the Sumida River police and firemen designated a park that had been an army clothing store as a safe place for anyone. About 40,000 people crowded into it. At four o’clock in the afternoon this place was hit with a firestorm and most of the 40,000 were killed.
At times in the past Japan has been suspicious of the value of western technology for the construction of earthquake resistant or earthquake proof buildings. On more than one occasion they noted that the simple wooden buildings used by farmers were able to withstand the shaking from an earthquake much better than brick or concrete structures. During this terrible disaster of 1923, one building that had been designed by an American architect stood firm when everything around it collapsed. The architect’s name was Frank Lloyd Wright and the building he had designed was the Imperial Hotel, still today a landmark in downtown Tokyo.
The interesting thing about this man was his adoption of Japanese ideas in his work, ideas that later would be known as organic architecture. Wright had designed the Imperial by floating it on a bed of piles that had been sunk into the ground. He then reinforced the walls with steel bars and divided the whole structure into sections each of which could move independently during an earthquake. At noon on September 1, 1923, two hundred dignitaries were having lunch in the Imperial to celebrate its opening. The luncheon ended abruptly as the earthquake stuck but the Imperial Hotel stood firm.
Japan has always been prone to earthquakes because it stands on the Eurasian Tectonic Plate, and is subjected to pressure from another two, the Pacific and the Philippine plates, both of which are continually sliding under it. The southern Kanto region has had two shocks of magnitude 7.8 or more during the past one thousand years. One of these was this 1923 earthquake, the other arrived in 1703. Both occurred along the Sagami trough, a northeastern boundary of the Philippine Plate.
Although they both occurred in nearly the same region, the 1703 earthquake was significantly different in the distribution of coastal uplift and tsunami height as can be seen at the present time in the height of the marine terraces along the southern Kanto region. Both of these earthquakes are interpreted as the result of low-angle faulting with a thrust component at the plate boundary. The southern Kanto region has been uplifted at different times over the past six thousand years.
Major uplifts have been associated with earthquakes like those of 1703 and 1923. The recurrence rate of these is estimated at between 800 to 1,500 years. Thus it is unlikely that major earthquakes like those in 1923 and 1703 will occur in the future. It is a very different story when we examine the western end of the Philippine Plate. It is located on the other side of the Island of Honshu, to the west of Tokyo, around Suruga Bay, in a segment of the plate known as Tokai. Here there is a record of frequent earthquakes. This segment is sub ducting beneath the Eurasian segment.
The last earthquake happened in 1854 and, prior to that, in 1707. Both of these were of magnitude 8.4. At earlier stages, in both 1605 and 1498 earthquakes of similar magnitude, that is to say around 8, hit the region. All of that amounts to four massive earthquakes within 350 years but at irregular intervals. Because of these statistics Japanese geologists now talk about the coming Tokai twentieth century earthquake. They do not know when it will arrive but they feel the chances of one in this century are very high indeed.
When writing about present activities in the Tokai Segment they title their reports “The Earthquake of 20xx.” Japan has been making preparations for it for the past twenty-five years. They know that it will be extremely destructive when it arrives because the subduction zone within which it moves is very long. They also expect it to be stronger than the 1923 quake. They point out that past earthquakes in Tokai occurred every 110 years plus or minus thirty-three years.
In the year 2006 it was 152 years since the last earthquake and the region was overdue for another on the basis of past statistics. In 1978, the local legislature adopted a largescale earthquake countermeasure act and a year later declared the Tokai segment to be “An area under intensified measures against earthquake disaster.“ There is also persistent public education designed to show the expected effects of the coming Tokai Earthquake. Japanese geologists often refer to it as worse than Kobe, the devastating 1995 quake in the city of that name.
The endless battle with earthquakes in Japan creates an outlook and a pattern of research unmatched in any other country. The Tokai Segment, for example, receives continuous attention. Both its depth and the height of the land above it are measured regularly and more detailed measurements are made of one part of the segment where the two plates are locked. This is the part that will one day give way and cause an earthquake. Historical studies of past Tokai tsunamis enable geologists to assess their impacts from the wave records. Unlike so many western countries, Japan has maintained accurate records of past earthquakes as far back as 1700.
One expert made a prediction in 1999 based on the collection of measurements available at that time. He said in 1999 that there is a 40 percent chance of another Tokai earthquake before the year 2010. Other experts have said that, when the Tokai Segment gives way, there is likely to be 6,000 deaths, another 20,000 serious injuries, and one million buildings damaged. He also said that large areas would be shaken at a level of 7, the highest intensity level in the Japanese intensity scale.
One disturbing prediction says that the greatest shaking from the Tokai earthquake will occur close to the site of a major nuclear power station, the Tokai-mura power station. This was not a consideration in 1923 but it soon became one in the years following World War II as Japan greatly expanded its industrial base and needed lots of energy. Japan lacks significant domestic sources of energy except coal and must import substantial amounts of crude oil, natural gas, and other energy resources, including uranium. Japan’s nuclear output nearly doubled between 1985 and 1996, as Japan attempted to move away from dependence on oil following the 1973 Arab oil embargo. The Japanese government is committed to nuclear power development, but several accidents in recent years have aroused public concern.
During the past few years, public opposition to Japan’s nuclear power program has increased because of a series of accidents at Japanese nuclear plants, including a March 1997 fire and explosion at the Tokai-mura reprocessing plant. Other problems for Japan’s nuclear power program have included rising costs of nuclear reactors and fuel, the huge investments necessary for fuel enrichment and reprocessing plants, several reactor failures, and the question of nuclear waste disposal. Regardless, Japan plans to increase the proportion of electricity generated from nuclear to 42 percent within the next decade. Japan ranks third worldwide in installed nuclear capacity, behind the United States and France.
Over four decades have passed since Japan’s first commercial nuclear power plant began operation in Ibaraki Prefecture in 1966. As of today the nation has fifty-two reactors operating around the country with a total output of 46,000 megawatts. Nuclear power accounts for approximately one-third of the country’s total electric power output. As an island country, it is impossible for Japan to exchange energy with neighboring countries through power transmission lines or pipelines. Japan is also energy scarce, depending on foreign countries for about 80 percent of its energy resources.
These conditions are completely different from those of Europe or the United States; therefore, the government of Japan concludes that it is rational to continue making the fullest possible use of nuclear power generation as one of the mainstays of the nation’s energy supply. Nuclear power generation contributes to improved energy sufficiency and to the stability of the energy supply, in addition to playing an important role in reducing Japan’s carbon dioxide emissions.