Scientists say old Japanese papers show a huge magnitude nine earthquake struck north-western America 300 years ago. The writings report damage from a five-metre-high tsunami that washed on to the Japan coast on 26 January, 1700. Computer modelling allowed Kenji Satake of the Geological Survey of Japan and colleagues to model the size and source of the quake that created the wave. A magnitude nine event would, in a few minutes, release about as much energy as the US now consumes in a month. The simulations show the earthquake probably ruptured the full length of a fault, known as the Cascadia subduction zone, which extends more than 1,000 kilometres [600 miles] along the Pacific coast from southern British Columbia to northern California. Until fairly recently, this fault was thought to be benign by most scientists. But then a number of discoveries in North America revealed the fault can produce earthquakes of magnitude eight or larger at irregular intervals, averaging about 500 years.
The most recent of the earthquakes, dated by radiocarbon methods, occurred between 1680 and 1720. It was the Japanese documentation that tied the date specifically to 26 January, 1700.
Satake's team, which includes Kelin Wang of the Geological Survey of Canada, and Brian Atwater of the United States Geological Survey, reports its work in the Journal of Geophysical Research-Solid Earth, published by the American Geophysical Union.
Their findings are likely to affect the Pacific region's precautions against future earthquakes and tsunamis.
"At issue for North Americans," said Atwater, "is how to adjust building codes and tsunami evacuation plans to reduce losses of life and property in the event of a future magnitude nine earthquake in southern British Columbia, Washington, Oregon and northern California."
View: Full Article | Source: BBC News
