TOKYO (Kyodo) — The magnitude 9.0 earthquake that struck northeastern Japan on March 11 may have been caused by an active fault in the seabed, according to the results of a private study made available Friday, contradicting the prevailing view that active seabed faults are not directly involved in ocean trench earthquakes.

A group of researchers from Japanese universities including Toyo University and Hiroshima University has concluded that a 400-kilometer fault line off Japan’s northeastern coast may have been responsible for the March earthquake.

“In order to make quake predictions more realistic, information regarding active faults in the seabed should be taken into account,” said Takashi Tanaka, emeritus professor at Hiroshima University, who participated in the study.

The catastrophic quake, which left around 15,800 people dead and over 4,000 missing, has been categorized as an ocean trench earthquake, which are believed to be caused by the shifting of crustal plates deep below the seabed.

According to the study results, the epicenters of quakes in the area since the latter half of the 19^th century closely matched the location of the fault line that stretches offshore from Iwate to Ibaraki prefectures, the researchers said.

The researchers also believe another active fault off the coast of Hokkaido could cause a massive temblor in the future.

Their study shows that no major tremors have been recorded in the area along the newly discovered 120 km fault line located off the east coast of Hokkaido, suggesting that a powerful quake of around magnitude 8 could occur there.

The findings will be reported at a meeting of the Association of Japanese Geographers on Saturday.