This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu . The Pacific plate , which moves at a rate of 8 to 9 cm ( 3.1 to 3.5 in ) per year , dips under Honshu 's underlying plate , building large amounts of elastic energy . This motion pushes the upper plate down until the accumulated stress causes a seismic slip-rupture event . The break caused the sea floor to rise by several metres . A quake of this magnitude usually has a rupture length of at least and generally requires a long , relatively straight fault surface . Because the plate boundary and subduction zone in the area of the Honshu rupture is not very straight , it is unusual for the magnitude of its earthquake to exceed 8.5 Mw ; the magnitude of this earthquake was a surprise to some seismologists . The hypocentral region of this earthquake extended from offshore Iwate Prefecture to offshore Ibaraki Prefecture . The Japanese Meteorological Agency said that the earthquake may have ruptured the fault zone from Iwate to Ibaraki with a length of and a width of . Analysis showed that this earthquake consisted of a set of three events . Other major earthquakes with tsunamis struck the Sanriku Coast region in 1896 and in 1933
in 1933
1933 Sanriku earthquake
2011 Tōhoku earthquake and tsunami