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 (NanTro 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

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(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. into the boundary The measurements should also shed light between the on some important research questions. What Philippine and happens to the rocks, and the water they carry, Eurasian plates in the subducting plate? How does the strain (dark wavy lines released during an earthquake propagate to the in sandy-coloured surface? Under what conditions do earthquakes cross-section). trigger tsunamis? Previous drilling has helped to answer other questions about the behaviour

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Staying afloat The arrival of Chikyu, Japan’s has pulled up some to last into 2012 instead of 2009.

massive ocean-drilling vessel, 35,772 cores from In addition to the Chikyu, the IODP has come with some financial 1,797 boreholes. The IODP funds drilling tasks on headaches. IODP had originally mission-specific platforms. But Japan paid for Chikyu to be built, planned for Chikyu some worry that the huge sums but running it will take another ¥10 and the Resolution of money needed for Chikyu could billion (US$90 million) per year. to be working at the jeopardize other drilling projects. Most of these costs will be met by same time along the If the Chikyu cannibalizes money Japan and America, as members Nankai trough, 100 from IODP’s other missions, then of the Integrated Ocean Drilling kilometres off the “community support for the IODP Program (IODP), headquartered coast of Japan. could diminish significantly”, says in Washington DC. But research The Resolution Mike Coffin, a marine geologist at funders struggle to compete with was taken out of The JOIDES Resolution started life drilling for oil. Tokyo University and former chair the rich coffers of oil-drilling firms service in 2003 of the IODP’s science planning and their demands for ship crews when the Ocean have been nice symbolically to committee. and shipyard time. Last year, Chikyu Drilling Program ceased to exist. work together,” says Greg Moore Other IODP projects are already was chartered by an Australian The intention was to upgrade it for of the Japan Agency for Marine- facing challenges. This July, a company to look for oil off Kenya. the IODP, but it has languished at Earth Science and Technology in project that had planned to drill But the greatest casualty so a shipyard in Singapore ever since. Yokosuka. into the continental shelf off the far has been America’s JOIDES High demand for the construction The Nankai-trough drilling coast of New Jersey had to be Resolution. For years the Resolution of oil rigs has funnelled potential project has already been deferred delayed because of issues over the was the workhorse of the ocean- workers off to other projects, from a start date of 2006 to availability of the drilling platform. drilling community. In 1985 it was and it is not certain when or if September this year to help defray The next IODP expedition after converted to a research vessel for the Resolution will ever take part the effect of ever-inflating costs. Chikyu gets going will now not the IODP’s predecessor, the Ocean in the Nankai trough work. “It’s a With the Resolution also out of take place until next March, in the Drilling Program, and since then it pity, especially because it would action, the project is now expected equatorial Pacific. D.C. of plate boundaries. At the Parkfield site, for When Obara and his colleague Yoshihiro Ito palaeoclimate study in the Indian Ocean, and instance, scientists have drilled three kilometres discovered these low-frequency earthquakes in a seismogenic study in the Middle America into the San Andreas fault and found that rocks the shallower region of Chikyu’s drilling area, it trench off Costa Rica. Both require such deep there contain talc, which could explain the ease gave the mission a whole new target to study4. drilling that only Chikyu can do it. with which the plates slide along each other at In 2001, when Chikyu’s drilling was being And eventually, Chikyu could achieve one of those points3. planned, “no one had heard of these earth- scientific ocean-drilling’s greatest dreams. In At Nankai, excitement has grown in the past quakes”, says Greg Moore, also of the JAM- the 1960s, scientists envisioned an ocean drill- five years, after seismologists there discovered STEC. “We now know there is a lot of seismic ing project that could pierce Earth’s mantle. The earthquakes that generate very-low-frequency activity.” project, called ‘Mohole’, never got deeper than waves. Before that, it was generally thought By 2012, Chikyu may have spent as much 200 metres beneath the sea-floor — let alone to that a subduction system had ‘creeping’ time as it needs to study these and other details 10 kilometres, where the crust borders the man- regions that slid past other, and ‘locked’ zones of the Nankai trough. After that, project manag- tle. But one day Chikyu might try its own ver- in which pressure builds up. But using broad- ers expect that the ship will be in high demand sion of Mohole. To do so, it would need a costly band seismometers, Japanese scientists found for other missions. Two vying to be next are a extension of the riser from its current 2.5 kilo- seismic events at lower frequencies metres to 4 kilometres so that it could than had previously been detected, operate in the deep waters where the and in places thought to be devoid of mantle is closest. But it would be worth seismic activity. Taira speculates that it, says Kinoshita. “This is a long-held JAMSTEC these low-frequency earthquakes, dream of all mankind, or at least of all which are typically of magnitude 3 or Earth scientists.” ■ 4, relieve strain over the long term. David Cyranoski is Nature’s Asia- “It is clear they have something to do Pacific correspondent, based in Tokyo. with the earthquake cycle,” he says. The new-found earthquakes could 1. Dalton, R. & Cyranoski, D. Nature 426, 492– be partly caused by water carried by 494 (2003). 2. Ichinose, G. A., Thio, H. K., Somerville, P. G., the subducting tectonic plate, says Sato, T. & Ishii, T. J. Geophys. Res. 108, 2497 Kazushige Obara, at the National (2003). Research Institute for Earth Science 3. Moore, D. E. & Rymer, M. J. Nature 448, 795–797 (2007). and Disaster Prevention in Tsukuba. 4. Ito, Y. & Obara, K. Geophys. Res. Lett. 33, L02311 The water creates a clay-like formation (2006). that “acts like a cushion” to slow the action of the earthquakes, he says. A riser system will hopefully allow Chikyu to drill into Earth’s mantle. See Editorial, page 260.

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