The earthquake was centered on the seafloor 45 miles (72 kilometers) east of Tohoku, at a depth of 15 miles ( 25 km ) below the surface. The shaking lasted about 6 minutes.
On top of the destructive tsunami, there was Nuclear Power Plant meltdown. The tsunami knocked all of them down, causing it to release radioactive materials into the atmosphere.
However, the government announced warnings before the tsunami hit. Thanks to the warnings they were able to prevent many casualties. If there were no warnings, the number of casualties would have been significantly higher.