Terrifying tremors

By The Economist online

ON Friday March 11th a huge earthquake of magnitude 8.9 struck off the north-east coast of Japan's main island, triggering a tsunami seven metres tall. The earthquake is thought to be the largest ever to hit Japan, and the fifth-largest since decent records began in 1900. According to the US Geological Survey, 15 of the 16 largest earthquakes occurred in and around the Pacific "Ring of Fire". Fortunately, many of the biggest, known as "megathrust" earthquakes, as one tectonic plate is forced under another, have occurred in sparsely populated areas.