Japan's crippled nuclear plant at Fukushima needs to beef up safety measures to face the risk of a large earthquake, scientists said on Tuesday.

The alarm was sounded by a trio of seismologists in Japan and China, who say the risk is an indirect cause of the March 11 tsunami-generating super-quake.

"The security of the nuclear plant site should be strengthened to withstand potential large earthquakes in the future," the team said in a study published in a specialist journal.

The concern stems from a computer model of the crust and mantle lying under northeastern Japan.

Using a technique called seismic tomography, the team analysed data from a vast network of sensors which record waves of energy propelled through the ground by earth tremors.