Temperature data to reveal frictional heat generated by fault slip during the Tohoku earthquake

May 01, 2013 by Tim Stephens 
Figure shows the drilling site of IODP Expedition 343/343T.

With the successful retrieval of a string of instruments from deep beneath the seafloor, an international team of scientists has completed an unprecedented series of operations to obtain crucial temperature measurements of the fault that caused the devastating Tohoku earthquake and tsunami in March 2011.

Emily Brodsky, a professor of Earth and planetary sciences at UC Santa Cruz, helped organize the Japan Trench Fast (JFAST), which successfully drilled across the last year and installed a borehole observatory nearly 7 kilometers beneath the . UCSC research scientist Patrick Fulton was on board the Kairei, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), for the retrieval of the string of pressure and that was installed across the at about 800 meters beneath the .

This was the last phase of operations for JFAST, designed to investigate the huge slip (50 meters or more) on the shallow portion of the fault that was largely responsible for the Tohoku and tsunami. The data recovered from the sensors provide a very high-precision record of temperature at 55 different depths across the plate boundary. Many of the sensors also recorded water pressure.

Figure shows the temperature sensor assembly in the borehole. Total 55 temperature sensing loggers were installed and successfully retrieved after about nine-month measurement.

"We will be analyzing the data to characterize the amount of frictional heat on the fault during the Tohoku earthquake," Fulton said. "We'll also be closely investigating the effects of other processes within the subsurface, such as groundwater flow and seafloor movement due to aftershocks. It is exciting to finally have this amazing data in hand."

According to Brodsky, the entire project was unprecedented on many levels. "Nobody had done rapid-response drilling in the ocean, nobody had drilled anything substantial under 7 kilometers of water, nobody had placed an observatory in a fault that deep, and nobody had retrieved a string of instruments from that deep," she said.

The scientific drilling vessel Chikyu installed the observatory in a dedicated borehole that penetrated 855 meters below the seafloor in a water depth of 6897.5 meters during the Integrated Ocean Drilling Program (IODP) Expedition 343/343T, April-July 2012. Brodsky said the team was very worried after an earthquake occurred in the area in December, raising the possibility of an undersea landslide that could have buried the wellhead of the observatory. So it was a great relief when the instrument string was successfully recovered on April 26, 2013.

UCSC researcher Patrick Fulton (blue jacket) and other scientists examine the retrieved instrument string on the deck of the research vessel Kairei. Credit: JAMSTEC

The recovered sensors provide data that will be used to determine the frictional heat generated by fault slip during the Tohoku earthquake. Scientists will infer the forces on the fault during the earthquake from these measurements of dissipated energy. The new data are critical to understanding the causes of the large, shallow displacements during earthquakes that can generate devastating tsunamis. The JFAST observatory provides the first temperature measurements at a subduction plate boundary fault immediately after an earthquake.

Fulton described the recovery operation in an email from aboard the Kairei: "Everyone was overjoyed in the Kaiko ROV control room as we started to faintly see the observatory come into view and the words 'wa suranai 3.11' we had painted on the side of the observatory, which means: 'Never forget 3.11,' the day of the earthquake and tsunami. We then used the ROV robot arms to grab the sensor string and then pull the sensors out of the hole. It was a tense moment and I was extremely uneasy. There was a very strong possibility that the fault may have continued to move, [trapping] our sensor string. It was a few very long seconds until we realized that everything was coming out smoothly and we had probably recovered everything. A few hours later, under a starry night with a lightning storm brewing on the horizon, we had pulled the sensor string onto the boat and confirmed we had all 55 sensors."

Brodsky and Fulton will be busy analyzing the data over the next few weeks in preparation for the Japan Geoscience Union Meeting, May 19 to 24, when they will present some of the initial results.

Explore further: Coral reveals long-term link between Pacific winds, global climate

add to favorites email to friend print save as pdf

Related Stories

Geology student drills into Tohoku quake source

May 23, 2012

(Phys.org) -- For the past eight weeks, geoscience graduate student Tamara Jeppson has traded her usual commute, from her Madison apartment to Weeks Hall on the University of Wisconsin-Madison campus, for ...

Recommended for you

Methane is leaking from permafrost offshore Siberia

14 hours ago

Yamal Peninsula in Siberia has recently become world famous. Spectacular sinkholes, appeared as out of nowhere in the permafrost of the area, sparking the speculations of significant release of greenhouse ...

New discovery in Arctic is a very old clam

14 hours ago

The rapidly thawing Arctic Ocean may be a new frontier but some of the latest news from there concerns a clam that is believed to date back more than a million years.

Barren deserts can host complex ecosystems in their soils

15 hours ago

"Biological soil crusts" don't look like much. In fact, people often trample right over these dark, or green-tinted, sometimes raised patches in the desert soil. But these scruffy stretches can house delicate ...

Researchers on expedition to solve 'small island problem'

15 hours ago

Researchers from the Department of Electronic & Electrical Engineering are starting their new year with an expedition to the island of South Georgia to carry out research into improving weather forecasting. You can follow the team's progress on their blog. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.