Asked by: Richard O’Neill, Glasgow
The 2011 Tōhoku earthquake off the coast of Japan created a tidal wave 40m high and shifted the entire main island of Honshu east by 2.4m. More than 127,000 buildings collapsed and almost 16,000 people died. This magnitude 9.1 earthquake only released about 3 per cent of the energy of a theoretical magnitude 10 quake. But there’s an upper limit to how much energy you can store in the rocks.
Very large earthquakes release more energy, but it is spread over a much longer section of fault line. It’s doubtful that there are any fault lines on Earth big enough to release a magnitude 10 earthquake, but if one happened, you could expect the ground to shake just as hard as a magnitude 9, but for a lot longer – perhaps as much as 30 minutes.
Image caption: A tsunami roars into the city of Miyako, following 2011’s earthquake.