Why did the earthquake happen and what were the main effects?
The map shows the position and size of the Pacific plate. It is almost entirely composed of oceanic crust and has boundary relations with the surrounding continental plates such as the North American plate. What is not easy to see is what is happening where different sections of the plates meet each other. With the New Zealand quake it was clear that the plate boundary in the South Island was one in which the plates were sliding past each other. This is called a transform fault boundary. However, in Japan, the boundary is very different. How are earthquakes cretated at the plate boundary in Japan? East of the Japanese islands the Pacific plate is moving west north-west at about 8.2cm a year. Most of the earthquakes are caused by the Pacific plate being dragged down below the Eurasian plate creating a deep ocean trench off the coast leading to a subduction zone. This is a sort of conveyor belt carrying material deep into the earths crust. The oceanic crust, as it is under thrust below t
