Scientists discovered a large number of fissures and fault lines on the seabed that probably led in part to the huge scale of the tsunami that hit northeastern Japan on March 11, 2011.
Scientists discovered a large number of fissures and fault lines on the seabed that probably led in part to the huge scale of the tsunami that hit northeastern Japan on March 11, 2011.
The team of researchers said the fissures and fault lines were likely created under strong extensional stress in the continental tectonic plate.
When the magnitude-9.0 Great East Japan Earthquake struck, the formation of the extensional faults that coincided with the seismic movement of the plate boundary may have allowed the seabed crust to undergo larger deformations than otherwise, adding to the size of the waves that followed, the scientists said.
"The generation of the normal faults likely allowed the crust to move farther seaward," said Takeshi Tsuji, an associate professor of geophysics at Kyushu University and a member of the team. "That movement may have increased the height of the tsunami."
The researchers used Shinkai 6500, a manned research submersible from the Japan Agency for Marine-Earth Science and Technology, to explore the seabed between depths of 3,000 and 6,000 meters off the coast of Miyagi and Iwate prefectures in 2008, 2011 and 2012.
They discovered a multitude of open fissures and normal faults off Miyagi Prefecture.
High heat flow, partly attributable to the presence of hydrothermal vents, was measured in August 2011, near one of the faults. But the heat flow subsided by 2012, which indicated that the fault likely slipped during the giant earthquake of 2011.