Rock the size of mountain under Japan may be causing megaquakes 

Japan is a country known for being seismically very active. The citizens suffer from earthquakes many times in a short span of few years. Now, scientists think an underground rocky mass the size of a mountain may be the cause of huge earthquakes in southern Japan.

Researchers have found the structure, called Kumano Pluton is beneath the coast of southern Japan. 3D visualisation of the Kumano Pluton has revealed that tectonic energy from megaquakes seems to be diverted to several points along its side.

"We cannot predict exactly when, where, or how large future earthquakes will be, but by combining our model with monitoring data, we can begin estimating near-future processes," says geophysicist Shuichi Kodaira of the Japan Agency for Marine-Earth Science and Technology in Japan. He was quoted by University of Texas at Austin website.

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To understand true extent of the Kumano Pluton, scientists examined 20 years of seismic data. The painstaking work included millions of recordings from Japan network of seismic sensors.

The biggest ever seismic data set was then fed to LoneStar5 supercomputer at the university.

Kumano Pluton is very dense and rigid and researchers think it contributes to the tectonic activity that causes earthquakes

Huge earthquakes of more than 8 intensity have been observed to have originated on the flanks of the Pluton in 1944 and 1946.