Scientists drilling into the fault responsible for the powerful earthquake and tsunami in Japan in 2011 have discovered why the quake was so much bigger than expected.
The disaster claimed at least 12,000 lives, destroyed 85,000 homes and triggered a meltdown at the Fukushima nuclear plant in northeast Japan.
A geologist at the Otago University in New Zealand involved in the study says it was previously thought that earthquakes release about 10% of stress built up when tectonic plates slide under each other.
However, Virginia Toy says they have discovered that the Japan quake released almost all the stress in one go, creating a tsunami so big that it topped protective sea walls.
Dr Toy says the findings mean disaster planners and authorities need to be prepared for much bigger quakes and tsunamis than previously thought.
The research has been published in the journal Science.