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20.9 News Feat Drilling PJ NEWS FEATURE NATURE|Vol 449|20 September 2007 IN THE ZONE The world’s biggest, best- equipped research drilling vessel is about to set off on its first scientific voyage. David Cyranoski previews its quest to catch a formidable earthquake in the act. hen it comes to natural disas- pipe — making the rig more stable and ena- Japan, which footed the bill for building ters, the Japanese government is bling it to drill more than three times deeper Chikyu, has a good reason to focus on the good with numbers. It expects, than any other scientific drill ship1. Nankai trough. Here, the Philippine tectonic JAMSTEC Wfor instance, a magnitude-8.1 But once Chikyu gets down to its ultimate plate dives beneath the Eurasian plate, on quake to strike in the next 30 years with an epi- goal — an earthquake-generating zone some six which Japan sits, at a rate of about four centi- centre in the Nankai trough — a depression in kilometres below the sea-floor — its work will metres per year. But at some points along the the sea-floor 100 kilometres off the country’s become very small-scale. Scientists onboard boundary, the plates ‘stick’ together and pres- east coast. And when it hits, it is likely to kill the vessel will be looking at minute changes sure builds. Two of these sticky patches, both between 12,000 and 18,000 people. in the porosity and other characteristics of the roughly 100 kilometres wide, were responsible The Nankai trough lies in a subduction zone, rocks drilled from the depths. Eventually, they for earthquakes in 1944 and 1946 (ref. 2) that a perilous region in which one tectonic plate will place instruments in a deep borehole that each killed around 1,300 people. And it is these dives under another, building up the sort of will gather data over several years. The goal patches that are thought to be where pressure rock strain that can unleash the world’s most is to monitor the build up of is building for the next big powerful earthquakes. All earthquakes with a strain in the rocks — to see an quake. It’s a good bet. For the magnitude of greater than 9 have occurred in earthquake in the making. “Having an exposed past 1,300 years the Nankai these zones. And although the next earthquake system to observe trough has unleashed a large at Nankai is not expected to be quite this big, Down under is like being able to earthquake, of magnitude 8 or the region could prove key in understanding Previous attempts have been greater, every 90 to 210 years. why earthquakes in subduction zones release made to monitor earthquake examine a live squid This regularity offers sci- such vast amounts of energy. zones — for instance, at the rather than a dried entists an opportunity for a On 21 September, a brand new research ship Parkfield site in California atop one.” — Asahiko Taira before-and-after look at an is due to depart from the city of Shingu in Japan the infamous San Andreas earthquake in a subduction on the first leg of a five-year project. The ini- fault — but Chikyu will be the zone. “There’s no place in the ative, called the Nankai Trough Seismogenic first to take such a precise look in a subduction world like it,” says Taira. Zone Experiment (Nan Tro SEIZE), is the latest zone. “It will be the first chance to see how such Going deep is the best way to study the and most ambitious of a series of deep-drill- an earthquake is being prepared,” says Asahiko trough. Using the riser system, Chikyu scien- ing research projects that stretch back decades Taira, director-general of the Center for Deep tists intend to dig the ‘ultimate’ borehole. (The (see ‘Staying afloat’). Everything about the ship, Earth Exploration in Yokohama, Kanagawa, record for the deepest scientific hole in the named Chikyu for ‘Earth’, is large: its 210-metre which manages Chikyu and its attempts to ocean is held by the JOIDES Resolution ves- length, its 10 kilometres of drill string and its unearth the very origins of earthquakes. “Hav- sel, which drilled to a depth of 2,111 metres ¥60-billion (US$526-million) price tag. Chikyu ing an exposed system to observe is like being in 1993.) Chikyu will also drill at least 5 other is the first research ship to use a massive pipe able to examine a live squid rather than a dried boreholes along a 70-kilometre line, spanning known as a ‘riser’ to encompass the main drill one to understand its biology,” he says. a range of depths above the plate boundary 278 NATURE|Vol 449|20 September 2007 NEWS FEATURE (see graphic). “We can look at temperature, will provide valuable information about the geo- pressure, material composition, as well as logical history of the region. The layers within the degree of dehydration, and see how these the cores “are like tree rings”, says Tobin. “You properties change from the shallow part of the don’t want to miss any dates.” But coring is a IODP/JAMSTEC plate boundary into the deep,” says Masataka slow process — every nine-metre section must Kinoshita, a researcher at the Japan Agency for be hoisted up into the ship before drilling can Marine-Earth Science and Technology (JAM- continue. Raising a core can take as little as 15 STEC) in Yokosuka and a chief project scientist minutes, to more than an hour, depending on for NanTroSEIZE. the depth of the water at the drill site. But those comparisons will have to wait until Because of the premium on ship time, the the project is completed, which won’t be before crew will work around the clock. A helicopter 2012. The leg starting on 21 September is an will make runs every two weeks from the shore 8-week-long rapid survey of the six planned Chikyu’s cores will provide unprecedented to exchange scientists and drilling crews. In the borehole sites. The 16 scientists on board will information about earthquakes around Japan. end, Tobin says, it will take six or more legs of use sensors attached above the drill bit to pick concentrated eight-week drill stints to reach all up signals such as γ-radiation, electric cur- leg will involve penetrating to a depth of 1,000 the way down to six kilometres. rents, and sound waves transmitted from the metres at two other sites. Half of the cores will be analysed on board; drill to obtain information about the poros- After that, Chikyu will be temporarily side- the other half will be stored in a facility at Kochi ity and density of the surrounding rock. “We lined, partly because of an agreement with University, on the island of Shikoku, for perma- can record information about Japan’s fisheries, partly to save nent archiving. Onboard researchers get first the rock types before we’ve dis- money and partly to do mainte- dibs at studying them, but a year after being turbed them,” says Harold Tobin “We can record nance work. Drilling is slated to extracted anyone can apply to study them. of the University of Wisconsin information about resume again in October 2008, in Madison, the project’s other the rock types when the massive riser system Detectors in the depths chief scientist. “This is about as will come into play. A riser, But many scientists are more excited about close to pristine conditions as before we’ve common on oil-drilling vessels the possibilities once the drilling has finished. you can get.” disturbed them.” but rare for scientific missions, Project scientists plan to place long-term To keep the project moving — Harold Tobin surrounds the drill pipe all the observatories down some of the boreholes to at a fast pace, no cores will be way from the ship down to the measure rock tilt, seismic activity, strain, pore taken. That will be the task of the sea-floor and below. Heavy mud pressure and temperature — key variables for next leg — a 4–5 week mission scheduled for is circulated at high pressure between the riser understanding how the rocks behave. The sen- late November. One of the cores will go down and the drill pipe to stabilize the rocks and stop sors must be designed to withstand very high to 1,000 metres, and they will all be analysed them from collapsing. temperatures, and will cost around ¥1.5 bil- with Chikyu’s plush scientific facilities, which The ship will recover lion over the next five years to develop. It’s not include a computed-tomography (CT) scanner cores in continu- yet clear whether they will be ready before that can reveal the internal structure of the core ous nine-metre Chikyu finishes its drilling. The research- without destroying it. In late December, a third stretches, which ers hope to operate the sensors for at least five years after they have been installed, perhaps uploading their data to remotely operated submersibles or JAMSTEC sending them back to shore via cables JAPAN on the bottom of the ocean. The observatories will measure changes that are surprisingly small Nankai trough given what can be felt on the ground during earthquakes. But “these measure- ments will be the key to getting a quantitative Chikyu will drill description of how the earthquake is building boreholes through its energy,” says Kinoshita. Over the long term, sediments Taira adds, the observatories might even be washing off able to provide a way to identify the very start Japan’s coast of earthquakes, and perhaps even to warn areas (upper left), and that have not yet been hit.
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