wide. so what causes sum unimaginable power? david rusk is a regional executive for the u.s. geological survey. thanks very much. as i understand it japan sits atop four tech tonic plates. what causes the shift? >> the earth's interior is hot. a lot of plastic and core is molten, there is a constant series of movement what we call the tettonic plates. in the case of japan, these forces are causing one of the plates to dive beneath the other. pacific incarcerate is moving underneath the other. they don't slip on a constant rate. they will build up strained energy and then suddenly slip in