Japan is situated in the collision zone of at least four lithospheric plates: the Eurasian/Chinese Plate, the North American Plate, the Philippine Plate and the Pacific Plate. The continuous movements of these plates generate a lot of energy released from time to time in earthquakes and tsunamis of varying magnitude and effects (Geologist Callan Bentley discusses in great detail the geological setting of the Japanese Islands).
Written records of strong earthquakes date back at least 1.600 years. Until 1860 however Japanese naturalists were less interested in exploring the cause of earthquakes than the effects of such an extraordinary event and mythical explanations prevailed.
In the year 1600 the Japanese nobleman Tokugawa Ieyasu choose the village of Edo (modern Tokyo) as his new residence and three years later it was the capital of the unified Japan. The city rapidly grew and soon reached hundreds of thousands of inhabitants - one of the largest cities at the time. Unfortunately this strategic position at the bay of Tokyo was and is still today a seismic active area.
Fig.1. Copper engraving published in 1669 by an anonymous European artist, possibly illustrating an earthquake in Edo in the year 1650. It is not clear if the artist experienced the earthquake himself or based this figure on eyewitnesses' accounts, nevertheless it is one of the oldest known illustrations of a Japanese earthquake (image in public domain).
December 31, 1703 Japan was hit by a strong earthquake with a reconstructed intensity of 8 after the Mercalli-scale. In Edo most of the wood buildings collapsed. The earthquake and its aftermath effects, like floods and fires, killed estimated 150.000 people. More than 6.500 people were killed by a flood wave, which caused havoc in the bay of Sagami and on the peninsula of Boso.
One of the most important historic earthquakes hit Tokyo November 11, 1855, killing 16.000 to 20.000 people. This event and the aftermath are retold by hundreds of woodcuts, especially in the form of a namazu-e.
Fig.2. and 3. Anonymous contemporary woodcuts showing Edo before and after the great Ansei-Edo earthquake (images in public domain; source "Documenting Disaster: Natural Disasters in Japanese History, 1703-2003", Foundation for Museums of Japanese History, Chiba 2003).
October 28, 1891, the agricultural region of Nobi experienced an earthquake of magnitude 8. Modern buildings and traditional houses were damaged or collapsed, thousands of people lost their homes and 7.000 people were killed.
The English geologists John Milne (1849-1913), who in 1880 founded the Seismologists Society of Japan, studied the effects of this earthquake and published an important monographic work "The great earthquake in Japan, 1891". The Japanese geologist Bunjiro Koto observed a superficial dislocation during the same event and recognized a fundamental principle in seismology - faults are not the result of an earthquake, but movements along a fault cause the seismic waves.
During the second half of the 19th and beginning of the 20th century scientific research on earthquakes became rapidly established in Japan.
Fusakichi Omori (1868-1923), director of the Seismological Institute of Japan, studied the occurrence of earthquakes around Tokyo and noted in 1922:
"Currently the immediate area of Tokyo is seismically quiet, while in the mountains around Tokyo, in a distance of about 60 kilometres, there are often triggered earthquakes, which - although they are may felt in the capital - are in fact harmless, because the affected areas are not part of a larger destructive seismic zone.
Over time, the seismic activity in these areas will gradually diminish; meanwhile it will increase in the bay of Tokyo and will possibly cause a strong earthquake. An earthquake with an epicentre at some distance from Tokyo will have a local, however destructive impact."
One year later, September 1, 1923, the city of Yokohama and Tokyo were hit again by an earthquake, today remembered as the Great Kanto- earthquake. More than 99.000 people were killed by the collapse of buildings, a 10 to 12m high tsunami and fires. The bodies of more than 40.000 victims were never found.
Fig.4. "A good idea of the tremendous devastation in Tokyo wrought by earthquake and fire. Enclosed find a few snaps taken on the top of the Imperial Hotel in Tokyo which is the only hotel in the earthquake district that survived." J.H. Messervey, letter dated March 5, 1924; image in public domain from the U.S.G.S. Photographic Library.
June 28, 1948 the American photographer Carl Mydans visited the city of Fukui to document the post-war development of this important industrial region. At 17:14 local time Mydans was surprised by a strong earthquake in the American military base, he remembers:
"The cement of the floor crashed. Dishes and tables were spun into our faces and we all found us involved in a mad dance…… when I found myself near the door, I moved into it's direction. But the floor slipped away under my feet and I rushed against a crumbling wall."
Mydans turned back to get his camera and in the next fifteen hours documented the desperation and destruction of Fukui. More than 5.131 people were killed. According to Mydans most of the victims perished entrapped under the debris and in the fire after the earthquake. Mydans later promoted the distribution of emergency tool boxes, equipped with an axe and other heavy utensils to remove debris.
In January 1995 the industrial city of Kobe was hit by an earthquake with a magnitude of 7.2 after Richter, the strongest earthquake in Japan since 1923. More than 6.000 people were killed and more than 300.000 people lost their homes.
Fig.5. Simplified map of Japan showing a selection of earthquakes with a magnitude greater than 7 after Richter in the last 100 years and major historic events (data from U.S.G.S. 2005, earthquake data from "Exploring Africa's Physical and Cultural Geography using GIS", see also "Seismicity of the Earth 1900-2007, Japan and Vicinity").
The devastating tsunami of March 11, 2011 was triggered by the strongest ever recorded earthquake in historic times, still one year later aftershocks are concentrated in the region where it generated.
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