THE December 26, 2004 Asian tsunami is a reminder of the dangers presented by the Ring of Fire around the South Pacific (see 'After the Tsunami' in last month's issue). Japan is an important part of that hazardous region. The Japanese archipelago is located in an area where several continental and oceanic plates meet. About 80 per cent of the world's major earthquakes take place along the Pacific Rim: the belt that extends from Chile, northward along the South American coast through Central America, Mexico, the US West Coast (including San Francisco), the southern part of Alaska, across to Japan, then down to the Philippines, Papua New Guinea and New Zealand.
This is the main cause for frequent earthquakes and the presence of many volcanoes and hot springs across Japan. If earthquakes occur below or close to the ocean, they may trigger tidal waves (tsunami, which after all is a Japanese word). Scarcely a day goes by without a tremor in some part of Japan. The country has about 3,000 tremors per year. 10 per cent of the world's earthquakes take place in Japan. It is the world's most earthquake-prone country as was shown only last month: on 20 March a strong earthquake struck Japan's southernmost island but fortunately casualties were minimal. It is also one of the world's best locations for keeping a record of earthquakes: its records go back to the twelfth century. This article recalls one of the worst earthquakes of recent centuries and looks at the implications for today.
The 1923 Tokyo Earthquake
The Tokyo earthquake was one of the world's worst disasters and the worst earthquake in Japanese history. In just five minutes the earthquake released more energy than was to be used in the entire Second World War. The shock waves were equivalent to 300 times the power of the 1945 Hiroshima bomb.
On Saturday 1 September 1923, at two minutes before noon, the earthquake hit the densely populated area of Tokyo and Yokohama on the huge Kanto Plain. The shocks reached between 7.9 and 8.3 on the Richter scale and were recorded as far away as the Lake District in England, Berkeley in California, Washington DC and Hilo in Hawaii (itself the victim of tsunamis in the 20th century). The damage caused by the fires that broke out was far worse than that caused by the earthquake itself. (The two largest peacetime fires in modern history--1906 in San Francisco and 1923 in Tokyo--were both caused by earthquakes).
The day began with heavy rain. In late morning the weather started to clear. Tokyo residents were getting ready for lunch and so there were charcoal stoves working across the city. The earthquake's epicentre was in Sagami Bay, about 50 miles south of Tokyo. The earthquake was followed five minutes later by a huge tsunami, with a height of about 36 feet (the southern edge of the tidal wave reached the coast of Ecuador, off Latin America). Over the next two days there were about 1500 aftershocks.
The overturned charcoal stoves and other fires ignited the ruptured gas pipelines and set light to the wooden buildings. The buildings were made from wood and paper to be flexible enough to cope with ordinary earth tremors. Unfortunately, although these structures may have survived against small earthquakes, they were vulnerable to fire, as stoves and braziers overturned, igniting straw mats and rice-paper screens. The houses were built close to each other with hardly any space between them.
A firestorm swept across the city. 75 per cent of all buildings suffered severe structural damage. The earth's movement cut most of the water mains and so where fire officers were able to respond to alarms, their hoses had nothing to carry.
People had no place to escape to. Over 140,000 people were lost from an urban population of about 4.5 million. 15,000 people were killed within the first two minutes. But the real problems were only just beginning.
Most were killed when the fires began. …