AT 2.46pm on March nth 2011, an earth-x.quake of magnitude 9.0 was recorded approximately 30km (18 miles) below the floor of the Pacific Ocean off Sendai, about 300km north-east of Tokyo. It was the most powerful earthquake ever recorded to have hit Japan, and scientists later determined that movement in the same subduc-tion zone caused the "Jogan quake" of 869, as well as related activity in 1896 and 1933. Like the recent "Great East Japan Earthquake", as it has become known, that ancient earthquake more than a millennium ago generated a monster tsunami in its wake. Not having the precise instruments that recorded 40-metre-high waves in 2011, villagers in centuries past have placed stone markers along the hillsides roundabout to show how far the wall of water swept inland.
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