It was found that the 2011 magnitude 9.0 Tohoku-Oki Earthquake ruptured the interface between two tectonic plates and large amounts of fluid flowed from deep in the earth to the sea floor along the plate interface. While the nature of the fluid is not well understood, it may trigger the great earthquake as the fluid would increase the pore pressure. Geochemical information in this fluid may clarify the mechanism behind earthquake occurrences.