A research team says a newly discovered undersea fault may have magnified the massive tsunami that struck northeastern Japan last year.

The March 11th earthquake triggered tsunami measuring more than 20 meters, which swallowed large swaths of Pacific coastline along Japan's Tohoku region.

Scientists originally thought the series of tsunami were triggered mainly by the movement of an ocean plate and the overlying plate carrying northeastern Japan.

But the displacement of the tectonic plates alone failed to explain why a 20-meter high tsunami was generated along the northern part of the Tohoku coast, including Iwate prefecture.

The research team led by Hiroshima University Professor Emeritus Takashi Nakata discovered a previously unknown active fault lying some 500 kilometers north to south along the coast of Iwate to Ibaraki Prefectures.

The team says if movement occurred along this fault, the height of the tsunami in northern Tohoku would reach about 20 meters, which actually happened.

Scientists say a number of undersea faults have also been discovered in other areas off the Pacific coast of Japan, where mega-quakes are predicted.

Professor Nakata says more research is needed into undersea plates to better prepare for possible future tsunami.