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Field Update: Return to the Japan Trench

[Editor's Note: Patrick Fulton is a researcher at the University of Texas at Austin's Institute for Geophysics. He was part of an expedition last spring aboard a deep sea drilling ship to study the fault near Japan that unleashed one of the largest earthquakes in recorded history in 2011. That expedition ran into technical difficulties and so now the team has returned to finish the job. For the next few days, Fulton will be sending updates from the ship on the progress of the follow-up expedition. This is his first installment.]

JFAST2 - Workers on ChikyuGreetings from the scientific deep sea drilling vessel Chikyu and the second part of the Japan Trench Fast Drilling Project: JFAST2 – IODP Expedition 343T. The focus of the JFAST project has been to quickly drill into and study the fault that slipped more than 50 meters at shallow depths during the March 2011 M9.0 Tohoku Earthquake and caused the devastating tsunami.

In April and May, we (an international team of ~30 shipboard scientists along with a number of engineers, ship/drilling crew, and onshore support) successfully drilled across the plate boundary fault at ~820 meters (0.5 miles) below the seafloor in water depth nearly 7 kilometers (4.3 miles) deep. This ended up being the deepest below sea level any scientific ocean drilling project has ever gone. We actually did it twice! – the first time we used logging tools to map the geology as we drilled allowing us to pinpoint the fault, we then drilled another hole and collected spectacular core samples through the fault zone. The analysis of the rocks and data are already providing important insight into the mechanics of large earthquakes and tsunamis and will undoubtedly continue to be fruitful for many years to come.

Now I have returned to Chikyu to help undertake the other main goal of the JFAST project, to install a subsurface observatory that will measure the frictional heat signal remaining from the Tohoku earthquake. By measuring the extra heat across the fault at depth we can back out how much frictional resistance the fault had during the earthquake and possibly gain insight into why it slipped more than 50 meters at our study location.

Together with the other JFAST analyses, this unique and important data will not only help us understand the fault and earthquake here, but may also help us understand the potential hazards at other large faults like the Cascadia subduction zone fault off the Pacific Northwest of the United States and British Columbia, Canada.

During the first JFAST expedition, we had many technical problems associated with trying to drill in such deep water for the first time and many delays from weather that prevented us from installing an observatory in the time window we had. We now have been fortunate enough to be given the opportunity to return for one last try.

Chikyu - JFAST2 - Day 4After flying on board Chikyu by helicopter and transiting North for a couple days, we are now on site and starting to lower pipe down to the seafloor. We plan to then drill across the plate boundary fault once again and then install our observatory of subsurface temperature sensors in the remaining hole. There are many unique challenges with installing such an observatory and with drilling in such deep water depths, but we are all ready and excited to try our best on this difficult mission so we can continue to learn as much as we can from the devastating Tohoku earthquake.

Stay tuned . . . more to come shortly.

- Patrick Fulton

Read all the posts in this series:

July 9: Field Update: Return to the Japan Trench
July 13: Field Update: Like Threading a Needle from 7 kilometers away
July 13: Field Update: Drilling Through the Japan Earthquake Fault

 

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