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German vessel sets out to explore quake-struck seafloor off Japan

One year after the devastating Tohoku earthquake and tsunami, Japanese oceanographers and geologists are teaming up with German scientists to uncover any traces that the the magnitude-9 quake might have left on the sea floor. The scientists will search for geomorphological evidence of what exactly happened on 11 March last year during the two-and-a-half-minute rupture that released massive amounts of seismic energy and triggered a deadly tsunami off the northeastern coast of Honshu.

The 33-strong crew, led by Gerold Wefer of the University of Bremen, will set out on 8 March from the port of Yokohama on a four-week expedition aboard the German research vessel the Sonne (pictured). The German science ministry is providing €1.5 million (roughly US$2 million) to fund the cruise, with German and Japanese funding agencies providing additional support. You can follow the expedition here.

The team will use the Bremen-built MARUM-SEAL, an unmanned submersible equipped with advanced sonar technology, to map in great detail the 2,000-metre-deep sea floor around the quake epicentre. Japanese scientists mapped several segments of the sea floor in 1999 and 2004. The Sonne crew will re-map the same profiles, to allow scientists to compare sea-floor morphology before and after the quake.

Scientists suspect that the extraordinary force of the tsunami, which killed some 20,000 people, may have been the combined result of the sea floor rising with a jolt by up to five metres and of quake-triggered slides of the Japanese continental shelf. The team will search for clues of either mechanism: the fine-scaled pattern of horizontal and vertical displacement of the crust beneath the ocean floor and the amount and origin of sediment that may have slid into the 7,000 metre-deep Japan trench will shed light on the fateful chain of events and help constrain the precise source of the tsunami, they hope.

“In the light of the tragic events last year the stability of the continental shelf off Honshu is a key research topic,” says Wefer. “We are glad that we can assist our Japanese colleagues with precious ship time. I hope that this cruise will mark the beginning of a close collaboration between our countries in marine sciences.”

The expedition will also target the sites of two drill holes made more than ten years ago by the US vessel JOIDES Resolution under the Ocean Drilling Programme. If the metal casings and electrical connections of the sealed drilling holes are still intact, the team will install there a set of instruments for recording seismic waves. For that purpose, the Sonne hosts the University of Bremen’s remotely operated diving vehicle MARUM-QUEST, which can operate in water depths up to 4,000 metres.

In a separate expedition, the recently modernized Japanese drilling ship the CHIKYU will in April drill into the fault zone and take temperature measurements near the epicentre of the quake to confirm various theories about friction in faults.

Image:  RF Forschungsschiffahrt Bremen.

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