What Is Below The Earth's Crust

What is below the Earth's crust?

ASK PIPPA Pippa Wysong Pippa Wysong

Section: Starship, pg. D11

The above question is from Vipal Jain, 12, of Mississauga.

The Earth is made of many layers, the top one being the crust. This is the part we live on. It is made mostly of different kinds of rock, especially granite.

The crust is 8 to 40 km thick, depending whether you're deep in the ocean or on a mountain.

Just below the crust is the asthenosphere.

According to geologist Arsalan Mohajer from the University of Toronto, this layer is made of extremely hot liquid.

"The crust is floating on semi-liquid rock," he said.

This layer of semi-liquid rock is up to 200 km thick. It the source of the stuff called magma that comes out of volcanoes.

Below the asthenosphere is the mantle, a huge area made up of rock, which reaches to a depth of about 2,900 km.

Mantle temperatures range from 100C near the crust, to 3,500C in the deepest parts.

The centre of the Earth is called the core.

The outer part of the core is melted liquid iron, while the inner or middle part is solid. The heart of the core sits 6,370 kilometres below the surface. That's about the distance you would drive from the east to the west coast of Canada!

Core temperatures range from a sweltering 4,600C (on the outer parts) to 6,600C at the centre!

Readers! Send a question. If it's used, you win a Starship backpack. Send to: Ask Pippa, Starship, the Sunday Star, One Yonge St. Toronto, Ont., M5E 1E6. E-mail: AskPippa @ hotmail.com.

Hole drills 2 miles into the fault zone

Scientists have made themselves a front-row seat in the theater of earthquakes.

Drilling was completed last week on an 8.5-inch-wide hole that goes more than 2 miles into an active seismic zone of the San Andreas Fault at Parkfield, Calif.

This 800-mile slit through California is the boundary between two moving parts of Earth's crust called tectonic plates. Parkfield is a tiny town well known for its earthquakes.

"As we were drilling, all of a sudden the drill rate jumped and all this gas started to come up. ... This gave us an indication that we were going through a fault zone," Gregory van der Vink says. He is project director for EarthScope, which is financed by the National Science Foundation to explore the structure and evolution of the North American continent in collaboration with the U.S. Geological Survey (USGS).

EarthScope has undertaken this first-of-its-kind endeavor called the San Andreas Fault Observatory at Depth, or SAFOD.

Scientists will place sensitive instruments deep into the hole to collect data, including fluid pressure, temperature and geophysical measurements, as small quakes develop and progress. This will help them understand the fundamental physics at play and predict larger, more devastating earthquakes, says geophysicist Mark Zoback of Stanford University.

"Trying to understand what happens right where earthquakes begin is one of the Holy Grails of seismology," says Kaye Shedlock, EarthScope program director.

The team drilled into an active seismic zone where small earthquakes -- about magnitude 2.0 -- occur every two years. During the 10- to 15-year life of the hole, scientists hope to monitor enough quakes to test predictability.

Earthquakes magnitude 2.0 and less are too small for people to feel and don't cause any damage. "It does have that limitation, but it's always a trade-off between size and getting to catch one in the act," says David Applegate, USGS senior science adviser for earthquake and geologic hazards.

Applegate says large earthquakes occur about once every 100 years in areas much deeper than the drill hole. Scientists are hoping that they will be able to scale up their findings to understand bigger earthquakes.

In addition to the instrument measurements, researchers collected material from the hole to study the composition of the fault zone. They will collect additional core samples starting in 2007.

Scientists also hope to learn more about the role earthquakes played in assembling North America. At San Andreas, the Pacific and North American plates grind against each other, moving about 2inches in a year (roughly the rate your fingernails grow).

Patches of these plates get stuck. When released, they quickly catch up to the rest of the plate. The energy released as these tectonic sections move is felt as an earthquake.

"Earthquakes are the signals of these plates constantly in motion. They are the processes that build mountains, that form ocean basins, that shape landscapes," van der Vink says.

"The project is going to have a profound influence," says Zoback, one of the principal SAFOD investigators. "We are opening a door to new areas of research that will pay off over time. We'll be learning things for months and years to come."

By Tom Spears

A top federal government geologist has found ruby deposits in Greenland in an expedition that raises the possibility of commercial ruby mines there, and also in Canada's Arctic and Labrador.

"In this particular area, the conditions have been favourable for forming a number of rare minerals," says Richard Herd, from the Geological Survey of Canada. Now, it's a question of seeing whether the rubies exist in deposits large enough for mining. He found deposits numbering in the double digits.

"It's like looking for gold," he said. "The gold is there, but it's the grade and the tonnages that make it an economically viable operation."

And, he said it's "a no-brainer" that similar rubies exist in some quantity in Canada, "somewhere in the Eastern Arctic (and) northern Labrador," which were once joined to Greenland until shifting plates of Earth's crust split them up and created the Davis Strait.

Herd made the latest Greenland finds in late July --building on discoveries he first made there as part of his PhD thesis research more than 30 years ago.

He knew back then there were rubies, but mining companies have only recently asked whether there are enough to mine. Hearing this, he asked his bosses to send him --as the world's top expert on those rocks in western Greenland -- to visit the region he hadn't seen since 1972.

"Just like in the past, when people knew there were diamonds somewhere in Canada but hadn't found the source rocks, there are suggestions that there are interesting gemstones all over Canada and it's just a question of concentrating some effort on finding them," the geologist said.

"It's not that the rocks aren't correct." Our Arctic rocks are exposed on the surface and are very similar to areas of southeast Asia where gems are produced.

The gems were produced by high pressure and heat of 800 to 1,000 degrees Celsius under a mountain range, he says.

"They've been sort of cooked, so what you end up with is a set of minerals that are very hard, and they're now back at the Earth's surface and they're popping out."

Rubies are aluminum oxide mixed with a little chromium. The chromium makes the red colour. (If they have titanium and iron instead of chromium they're blue --and sapphires).

Herd is curator of the national collections of Natural Resources Canada. His report to the geological surveys of both Canada and Greenland and Denmark is due in late September.

The rubies are in very old rock --some three billion years, near Fisknaesset, on the coast about 160 kilometres south of the capital, Nuuk.

It's rugged, rocky land cut by fjords. Walking over the terrain is rough, Herd said. "I was pleasantly surprised that I was able to do it."

The area of interest is about 50 by 100 kilometres.

The one place no one will find Arctic rubies is little Hans Island, subject to an ownership squabble between Canada and Denmark. "It's not the right geology," Herd said.

Source: Winnipeg Free Press (MB), Aug 16, 2005, pb7 Item: 7BS3158887598 The Quake That Shook the World

Studies of the large Sumatran earthquake that caused the devastating tsunami in December have shown for the first time that earthquakes can trigger smaller quakes as far away as the other side of the world.

On 26 December, an earthquake measuring 9.1 on the Richter scale hit off the Indonesian island of Sumatra, triggering a tsunami that killed nearly 300,000 people. Researchers knew that such large quakes might spark seismic events far away, but just how large and distant these events could be was unknown.

Now, seismologists led by Michael West of the University of Alaska, Fairbanks, have shown that 14 small earthquakes near Alaska's Mount Wrangell — nearly 11,000 kilometers from Indonesia — were related to the Sumatran quake. A network of seismometers around the volcano indicated that the ground started shaking about an hour after the Sumatran quake — due to surface waves traveling along Earth's crust. In addition, the Alaskan quakes occurred systematically every 20 to 30 seconds in sync with the waves from Sumatra, the researchers report today in Science. "We now know that earthquake triggering is a truly global phenomenon," says West. "A great earthquake such as [the one that hit] Sumatra can trigger seismic activity anywhere on Earth."

Joan Gomberg, an earthquake seismologist at the U.S. Geological Survey in Memphis, Tennessee, says that these kinds of observations may give seismologists clues to how other regions of the world may be affected by long-distance seismic events.

Related site

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By Marie Granmar

Copyright of Science Now is the property of American Association for the Advancement of Science and its content may not be copied without the publisher's express written permission except for the print or download capabilities of the retrieval software used for access. This content is intended solely for the use of the individual user. Copyright of Science Now is the property of American Association for the Advancement of Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Scientists probing tsunami location

Cameras being sent to floor of ocean

Scientists are investigating the site of the undersea earthquake that set off last year's tsunami in South Asia, the British Broadcasting Corp. and the United States' Discovery Channel said yesterday.

The broadcasters said in a statement that scientists hoped to compile a second-by-second account of the disaster using computer-generated images, from the first subterranean tremors to the moment of impact on shore. This will be shown in a two-hour documentary, Journey to the Heart of the Tsunami.

An international team of 21 scientists operating from a deep-water ship, the Performer, will spend 17 days researching the epicentre, where plates in Earth's crust collided beneath the Indian Ocean, the statement said.

Members of the team -- which includes seismologists, geophysicists, biologists and seabed visualization experts -- are sending cameras five kilometres to the sea floor to investigate the subduction area, where one tectonic plate is being forced beneath its neighbour.

"Heart of the Tsunami will be a genuine scientific inquiry of significant interest to geologists, physicists and seismologists, and indeed, to many branches of science in general," said Julian Ware, head of special projects at producers Darlow Smithson Productions.

"We expect to return with data that will be hugely beneficial to our understanding of such a phenomenon, while at the same time providing dramatic TV footage of the epicentre that triggered the tsunami."

The documentary will air in Britain and the United States later this year.

Copyright of Winnipeg Free Press (MB) is the property of Winnipeg Free Press (MB). Copyright of PUBLICATION is the property of PUBLISHER. The copyright in an individual article may be maintained by the author in certain cases. Content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Source: Winnipeg Free Press (MB), May 13, 2005, pa17 Item: 7BS3598907164 Divers to examine site of equake that set off tsunami

Scientists are investigating the site of the undersea earthquake that set off last year's tsunami in South Asia, the British Broadcasting Corp. and the United States' Discovery Channel said Thursday.

Source: Western Star, The (Corner Brook, NL), May 13, 2005, p9 Item: 94K2614334758 The Big Dig

Forget Yucca Mountain. It's time to drill a new grave for America's worst radioactive waste.

This is as good as it's going to get. If they need more proof, I'll be happy to make up more stuff." So wrote a government scientist, effectively penning the epitaph for Yucca Mountain, Nev. That's where the Department of Energy has spent two decades and $9 billion fighting to build a permanent depository for 70,000 tons of used fuel rods from the nation's nuclear reactors. Not anymore. The revelation that the case for Yucca may've been built on fraudulent science has brought on an FBI investigation and put the kibosh on the project indefinitely.

Funny thing is, for the last 20 years, there's been a pretty good solution for burying nuclear waste: deep borehole disposal. Monster drills would cut a hole a yard or so in diameter down 2.5 miles into the Earth's crust, past the deepest groundwater into granite rock formations that have sat undisturbed for billions of years. To the bottom would be lowered waste-bearing metal canisters a foot across and 15 feet long. Every hole could fit some 400 canisters, each containing a half ton of spent fuel, and would be topped with hundreds of feet of absorbent clays and concrete.

Borehole disposal was proposed in the 1980s but rejected because the technology didn't exist to dig that deep. Some geologists falsely believed heat from the waste could melt surrounding rock and form a radioactive volcano. Since then scientists at Los Alamos National Labs and MIT have concluded that, with more study, it could be a very safe disposal method. Already Finnish nuclear utility Posiva is test-drilling the rock beneath Olkiluoto island with the idea of interring waste one-third of a mile down. Sweden is considering its own plan.

Granite underlies much of the U.S., allowing for regional depositories that could cut the costs and risks of transportation. The worst of the nation's waste could fit in 300 boreholes. It still wouldn't be cheap; figuring at least $10 million to drill, case and load each hole would bring a total of $3 billion, before engineering and permit costs. Like Yucca, which Uncle Sam estimates would cost another $50 billion to make usable, the depositories would be funded by both taxpayers and the electric utilities that own power plants. The chief hang-up is political: the need to scrap a federal mandate that nuclear waste stowed anywhere must be retrievable for 100 years in case anything goes awry.

PHOTO (COLOR): a $9 billion hole: entrance to the Yucca Mountain nuclear waste repository in Nye County, Nev.

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By Christopher Helman

Copyright of Forbes is the property of Forbes Inc.. Copyright of PUBLICATION is the property of PUBLISHER. The copyright in an individual article may be maintained by the author in certain cases. Content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Source: Forbes, 5/9/2005, Vol. 175 Issue 10, p52, 2p Item: 16855953 Quake in December Set Stage for More Upheaval

Yesterday's massive earthquake occurred in a region that is prone to temblors because large segments of Earth's crust are colliding there, creating enormous pressures that are released periodically in cataclysmic jolts, geologists said yesterday.

Scientists had been expecting that another large quake might strike soon in the region because the massive undersea upheaval that triggered December's tsunami generated even more pressure on the region's already volatile geology, experts said.

"What happened today was not a surprise. A number of scientists have been talking about an increased likelihood of more earthquakes in this area because of the rupture that happened in December," said Lori Dengler, a geologist at Humboldt State University in Arcata, Calif. "And it may not stop here."

Earthquakes occur along the boundaries between sections of Earth's surface known as plates. These plates are constantly moving, slowly but inexorably pushing against one another.

"They are squeezing together over geologic time at about the rate your fingernails grow," said Alan L. Kafka, a geophysicist at Boston College. "The movement causes tremendous amounts of force to build up and up and up."

Eventually, rock in one of the plates gives way under the pressure, causing a section to snap and the plates to suddenly lurch.

"It's on these plate boundaries that we have the world's largest earthquakes," said Bruce Presgrave, a geophysicist at the U.S. Geological Survey's National Earthquake Information Center. "The rocks are stressed and stressed and stressed until finally they can't sustain it anymore and they snap, shifting to a new position. That's what we feel as earthquakes."

The area where yesterday's quake occurred is particularly troublesome because of the speed at which plates there are converging, and their relative positions. Unlike the San Andreas fault in California, where two plates are moving past each other horizontally, the region west of the island of Sumatra is a "subduction zone," where plates are sliding over and under one another.

"These are the places where we have most of the world's earthquakes, and lots and lots of volcanoes," Dengler said.

In December, a section of one plate about 700 miles long suddenly plunged about 30 feet beneath another, causing a magnitude 9.0 earthquake that created the devastating tsunami. That event probably increased pressure on the next section of the plate boundary just to the south, causing yesterday's similar sudden thrust of one plate beneath the other, this time apparently involving a smaller section of perhaps 200 to 300 miles. "We think it's very likely that the extra stresses put on by the quake happening to the northwest is very likely to have triggered this earthquake. It would have happened sometime, but the timing may have been moved up by the quake to the north," Presgrave said.

There is now an increased possibility that yet another massive quake could occur soon, farther along the same plate boundary, experts said.

"Think of a crack in your windshield that propagates over time," said Kate Hutton, a seismologist at the California Institute of Technology. "Once there's a break, the two ends are the most highly stressed and it eventually keeps growing."

The timing of the next event is unpredictable because it depends on a host of factors, including whether pressure had been released along the boundary by previous quakes. But more quakes are inevitable.

"It's just a question of when, and how big," Dengler said.

Scientists were unsure yesterday why this quake apparently did not cause a tsunami, but there could be a number of explanations.

If the temblor caused the seafloor only to vibrate, instead of suddenly shifting upward, that would have prevented a tsunami.

"The question is whether it actually shifted the seafloor itself. If the quake doesn't actually move the seafloor, and just shakes it, then you're not moving the water," Presgrave said.

Another possibility is that the force of whatever water movement occurred was dissipated by nearby islands or just moved out to sea. But scientists are studying the event for clues that might help them predict future tsunamis.

"This is a really important question," Dengler said.

Work is underway to create a tsunami warning system for the Indian Ocean similar to the one in place for the Pacific.

Edition: 5 - Final TOKYO: Researchers yesterday unveiled the world's largest earthquake simulator designed to help save lives, just days before the 10th anniversary of the devastating Kobe quake.

The machine would educate people on how to construct buildings better able to withstand movement of the earth's crust, a spokesman at the Hyogo Earthquake Engineering Research Centre said.

Today, the centre will host a symposium on mitigating earthquakes for seismologists from around the world and demonstrate its simulator.

The gathering coincides with this week's UN-sponsored World Conference on Disaster Reduction in Kobe, where world leaders and meteorologists will discuss establishing an Indian Ocean tsunami warning system and other measures to diminish the impact of natural disasters.

Source: Sunday Times, The (Perth), JAN 16, 2005 Item: 200501165037495158 Couldn't we solve the world's energy problems by tapping into the molten core beneath the Earth's crust?

Couldn't we solve the world's energy problems by tapping into the molten core beneath the Earth's crust? Unfortunately there is roughly 1,870 miles (3,000km) of semi-solid mantle underneath the crust before the molten outer core. The oft-used comparison is that the Earth's crust is like tissue paper on an orange, with the bulk of the fruit being the mantle. As to actually tapping the outer core, the technical problems are obvious. The deepest borehole to date is only a few kilometers depth into the crust. Even if it were technically possible, the motion of the outer core is thought to provide the Earth with its magnetic field, so removing its contents would have dire consequences for life on the surface as the magnetic field would weaken and perhaps vanish over time. As the liquid is under enormous pressure there would also be tremendous difficulty trying to cap such borings. I think we would be advised to let sleeping dogs lie.

Ian Broadhead, Wakefield, West Riding of Yorkshire

Poor efficiency is a good reason to try some other methods first, including solar power. While the Sun pours down more than 1,000 watts of power on every square metre of the tropical zones of Earth, and about 600 watts per square metre at the latitude of Britain, the average amount of heat flow from the Earth's interior is less than one watt. Mike Dworetsky, Stanmore, Middlesex

Diamond-studded journey to centre of the Earth

Scientists may use nuclear power to drive a probe 2,000 miles into the heart of the planet, reports Mark Henderson

One of the great science fiction epics of Jules Verne could soon become reality:

a leading scientist is planning to send a grapefruit-sized probe on a journey to the centre of the Earth.

The sensor, which would be made from diamonds to withstand temperatures of more than 4,000C, would be blasted into the bowels of the planet by a "reverse volcano" of liquid iron under plans advanced today by David Stevenson, Professor of Planetary Sciences at the California Institute of Technology.

Hundreds of thousands of tonnes of the molten metal would crack open the Earth's crust, kick-started by a nuclear explosion or artifical earthquake, and allow the capsule of instruments to be carried down 3,000km (1,860 miles) to the edge of the Earth's superheated core. The journey would take about a week.

The probe would send back the first direct data on the planet's heart, revealing details of the core's temperature, chemical composition and electromagnetic activity. The findings would be transmitted to the surface using seismic waves, the vibrations that cause earthquakes, because radio waves cannot penetrate such depths.

Scientists believe that the data would give valuable insights into the Earth's electromagnetic field, generated from its core, which protects the planet against solar radiation and makes modern satellite communications possible. There may also be implications for nuclear fusion research.

The project, set out by Professor Stevenson today in the journal Nature, would cost at least $10 billion (Pounds 6.2 billion) and would require years of international co-operation. A better knowledge of our own planet, however, is more important than the exploration of space, on which resources many times greater have been lavished, he says.

"Planetary missions have enhanced our understanding of the solar system and how planets work, but no comparable exploratory effort has been directed towards the Earth's interior. Space probes have reached a distance of about 40 astronomical units (6,000 million km, or 3,700 million miles), but subterranean probes have descended only some 10km (6.2 miles)."

The biggest challenge for a mission to the Earth's core would be cutting a path through the crust and mantle. The Earth's centre is 6,400km (4,000 miles) below the surface. The probe would have to travel about half this distance to reach the edge of the core.

Professor Stevenson's solution is to create a crack the height and length of the Empire State Building -300 metres (984ft) -but only a metre or so across. Into the crack would be poured at least 100,000 tonnes of molten iron alloy, and possibly up to 100 times more. This would create such stress on the rock below that it would force itself down under gravity, gouging a huge fissure that sealed itself at the top as it went. "You're talking about something that's a direct analogue of a volcano, just in reverse," Professor Stevenson said. "It's like plunging a huge knife of molten metal into the Earth's surface."

A nuclear explosion of several megatonnes, or another high-energy event such as an earthquake, may be needed to kick-start the metal's plunge. It might be possible to take advantage of natural fissures in the crust such as the volcanic vents of Iceland, from which Jules Verne's fictional expedition made its descent.

Iron would be used because it is cheap and abundant -100,000 tonnes is produced in an hour by the world's foundries -and because it would not react much with the iron-rich rocks. It would be molten to reduce friction, rather than because of the heat.

The probe would travel inside the liquid iron, and would have to be made of a substance that could withstand high temperatures. "Obviously you couldn't use conventional micro-electronics, but diamonds would work well because they're semiconductors at high temperatures," Professor Stevenson said.

It would carry instruments to measure temperature, the presence of different elements, and electromagnetic activity. "We just don't know what's down there apart from iron," he said. "There could be silicon, sulphur, oxygen, hydrogen, but we just don't know.

"It's an indispensible project, in the same sense as going to planets is indispensible. We see them with telescopes, but when we go there we find things that surprise us. I'm sure we will find things we didn't predict in the core as well. We might be able to explain how the Earth's electromagnetic field is generated, or the source of some volcanoes." There could be risks, such as opening up a fresh volcano or generating an earthquake but these could be minimised by careful study, he said.

Professor Stevenson said that his paper in Nature had been inspired in part by the recent film The Core, in which scientists played by Aaron Eckhart and Hilary Swank travel to the centre of the Earth to avert an environmental disaster.

"I had had the idea long before, but the movie triggered the writing of the paper," he said. "I was asked to comment on the science of the movie and, though the prospect of sending people there is obviously preposterous, it got me thinking again about how we could get a probe down there."

A more celebrated literary journey, however, is likely to give the probe its name. "You can bet Jules Verne is going to be the favourite," Professor Stevenson said, referring to the author of the literary adventure that on June 28, 1863, sent Professor Otto Lidenbrock of Hamburg, his nephew Axel, and their local guide Hans into the crater of an Icelandic volcano.

The intreprid group's mythical exploits were recounted the next year in A Journey to the Centre of the Earth, one of the first and most enduring works of the new 19th-century genre of science fiction.

According to Verne, Professor Lidenbrock was trying to retrace a trip made by a 16th-century Icelandic scholar, after he had found an ancient manuscript describing the route.

After climbing down through the Snaefells volcano, a peak of almost 5,000ft that lies about 70 miles from Reykjavik, the three men travelled deep below the Earth's surface. Along the way they encountered a vast underground sea, forests of giant mushrooms, fighting dinosaurs, a race of giants and living fossils.

Verne's centre of the Earth was a cool place, filled with caverns, seas and life.

Even in the late 19th century, however, most scientists believed, correctly, that the Earth became hotter with depth.

That understanding is also behind The Core, in which scientists discover that the Earth's magnetic field, which is generated by the Earth's core, is switching itself off, threatening disastrous consequences. Some of these are plausible - extra radiation from space and damage to computers and satellites -but others, such as bridges being wrenched apart by magnetic force, are not. To prevent a catastrophe, a team of "terranauts" are sent into the centre of the Earth.

Independent experts welcomed the ambition behind the real-world project announced yesterday, but doubted its practicality. "It would be hugely valuable, but there are some fundamental flaws," David Price, Professor of Mineral Physics at University College London, said.

"He's relying on the stresses breaking apart the rock, but as this happens you'd get heating and melting of the crack walls. This would slow everything down: the probe would continue to sink, but over a timescale of several thousand years. I'm also not convinced you could get a signal out using seismic waves, or even measure the temperature."

Copyright (C) The Times, 2003 Source: Times, The (United Kingdom), May 15, 2003 Item: 7EH3572969648 PLUMBING PLANETARY SECRETS

In Jules Verne's classic 1864 novel, Journey to the Center of the Earth, Professor Hardwigg starts his exploration by descending into a dormant volcano's crater, then hiking down a maze of shafts and passageways. Real-life geologists don't have the fictional convenience of a simple tunnel to the Earth's inner depths, but they've long fantasized about drilling one. That fantasy may soon become reality, now that Japan has begun constructing a giant drilling ship jokingly called the Godzilla Maru (Godzilla ship) by American scientists.

This huge ship will give geologists their first real shot at drilling completely through the eggshell layer that makes up the Earth's surface. Once they penetrate this thin crust, they'll be able to take samples from the underlying mantle, a mysterious layer of rock that extends 1,800 miles down to the moon-sized lump of iron at the Earth's core. Scientists know little about the Earth's mantle, even though it makes up most of our planet and its movements shape all of Earth's features, from its climate to the shape of its oceans and continents. Going to the mantle is an audacious plan that calls for drilling through at least 4 miles of solid rock beneath ocean waters over 2 miles deep. The feat is the geological equivalent of NASA's "moon shot," and indeed Earth scientists have been dreaming of it since the days of Apollo's glory. Because the crust that makes up the continents is 20 miles thick on average, they proposed drilling through the much thinner crust under the ocean. The idea generated excitement and even a brief race with the Russians, "Project Mohole"--named after the Croatian seismologist Andrija Mohorovicic, who discovered the boundary between the crust and the mantle. But the effort soon bogged down in political infighting.

Still, initial testing of ocean drilling in the 1960s proved that geologists could gather samples from beneath the seas. Since then, a drill ship, shared by an international consortium, has drilled over 2000 shallow holes. These expeditions have revealed a trove of information about plate tectonics, climate change, and bacterial life within the Earth. But going to the mantle soon earned the reputation of an impossible dream.

Then, in the early 1990s, Japanese researchers stepped forward with plans for a shockingly big drilling ship. At an estimated cost of $500 million, the 690-foot vessel will vastly outpower the consortium's ship. What's more, the ship will have "riser" technology now used by oil companies. Riser ships encase the drill bit in a pipe, allowing the driller to protect against accidental oil spills, to flush out debris, and to keep the hole from collapsing.

Japan's interest in ocean drilling can be summed up in one word: earthquakes. The new ship's primary mission is to investigate earthquake zones off the coast of Japan. But in the back of everyone's mind lies that holy grail, the mantle, which a vessel of this magnitude could conceivably reach. The world's ocean drilling community has once again made going to the mantle an explicit goal, and the operating costs of the vessel will likely come from the United States and other interested countries. Within 15 years, scientists hope to drill through a complete slice of oceanic crust.

Beyond trinkets. Geologists have mantle rocks sitting in their labs. Last year, for example, Australian geochemists announced that they'd stumbled on rocks that originated 435 miles beneath the Earth's surface. But rocks like these are "weird," as geologists put it, because they're sitting on land. An undisturbed sample taken from within the Earth would reveal more about the real composition of the mantle.

Naysayers argue that the Japanese ship will never reach the mantle with riser technology, which has never taken the oil industry so far down. While the ship will be complete in 2004 and will immediately start drilling shallow holes, Japanese researchers estimate they won't finish the equipment for going to the mantle until 2012. The drilling itself would then take a solid two years.

Even if scientists fail to reach the mantle, they expect plenty of discoveries trying. "We find out something new with every meter down we go," says James Natland of the University of Miami, who points to surprises like bacteria flourishing deep beneath the seafloor, where no one ever thought life could survive. Scientists probably won't encounter anything like the 40-foot mushrooms and crocodile-shark monsters discovered by Verne's explorers, but they do expect to unearth at least some of the secrets hidden inside the planet we call home.

In 2012, a giant Japanese ship is scheduled to begin drilling through the Earth's crust to sample rocks in the mantle underneath.

TECTONICS IN A SANDBOX

Researchers model the earth's motions at small scale

How do rivers cut their banks? For decades, hydrologists have used tanks filled with water and fine sand to find out. In many cases, experimenting with such small-scale physical models has proved superior to using computer codes, which often do not mimic nature nearly as well. That is why a group of researchers at the University of Minnesota's St. Anthony Falls Laboratory decided to build what may be the most elaborate modeling tank of this kind yet, one that allows the scientists to control more than the usual parameters of sediment type, water flow and level. The room-size device now under construction will also be able to imitate the way the earth's crust gradually shifts up and down. Tests of the concept have already produced scale models of continental shelves that, when opened up, look so much like cross sections of the real thing that petroleum geologists may learn something new about these vast reservoirs of oil and gas. Because the apparatus can simulate the evolution of subsurface geology, its builders have dubbed it "Jurassic tank." It was conceived by two of the university's faculty: Christopher Paola, a geologist, and Gary Parker, a civil engineer. When they first thought of building a tank that could model tectonic subsidence and uplift, they designed one with a hinged but otherwise rigid floor that could be jacked up and down in various ways. But after consulting with an engineering firm that fabricates earthquake simulators and similar equipment, they realized that their initial concept was essentially unworkable, even with their $500,000 budget.

Paola and Parker began to despair, but their hopes rebounded when James P. Mullin, an engineer in the lab, showed them something resembling an ant farm. Mullin demonstrated that the best way to make a flexible floor for a large tank was to use granular material that could be withdrawn from the bottom. "Like the agricultural feeders you see around here," Mullin notes.

After some experimenting, the team built 10 steep-sided funnels with hexagonal rims to test the idea. The researchers clustered the hexagons together in beehive fashion within a small tank, filled the cones with pea-size gravel and laid more gravel and a rubber mat on top. Pushing gravel out a little at a time from the bottom of the funnels (with a water jet) allowed them to move the rubber floor of the tank downward with a precisely controlled motion. The prototype worked so well that they then used it to simulate coastal deposition, introducing at one end fine sand and crushed coal so that the resulting light and dark bands would delineate discrete sedimentary beds.

As the flow of water transported these sediments across the model terrain and into the diminutive ocean pooled at the far side, the scientists adjusted the water level and withdrew gravel from the underside. In this way, they could simulate changing sea level and tectonic subsidence. The experiment succeeded, but it created another technical problem: how to dissect the slab of sediment resting on the rubber mat to reveal the "geologic" structure hidden within it.

Again Mullin came up with the solution. "He made essentially a big microtome," quips Christopher R. Ellis, a researcher on the Jurassic tank team. Like the microtomes used to slice biological specimens for microscopic analysis, the apparatus Mullin built shaves thin layers from the side of the model deposit. After each slice, photographs are taken, and the results are recorded on a computer, which can later render cross sections at any orientation.

The six- by 11-meter Jurassic tank, with its full set of 432 hexagonal funnels, should be complete by the fall. Although the tank will eventually be used to model other geologic settings, initial experiments will simulate sedimentation along continental margins. Once the slices are translated to a form that resembles the seismic cross sections used by oil- exploration geologists, Parker boasts, "we can produce images that will fool them."

PHOTO (COLOR): HONEYCOMB OF FUNNELS will hold enough gravel to support a rubber floor for the giant modeling tank being built by University of Minnesota researchers.

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By Daved Schneider

Source: Scientific American, Jul98, Vol. 279 Issue 1, p36, 1p Item: 710419

THE BLOB FROM BELOW

It's big, it's hot and it's rising beneath Europe and North Africa. Fortunately, it's not some protoplasmic cousin of Godzilla, but an immense, sheetlike flow of hot mantle rock from Earth's interior. And although this mantle current poses no threat to man or beast, it may force scientists to reconsider present-day ideas about Earth's deep plumbing system.

Geologists detected the flow using seismic waves from earthquakes to piece together a picture of Earth's mantle, the layer of hot rock that surrounds the planet's core. When these waves pass through hot regions, they slow down slightly. By combining seismic data from many sites around Europe, the scientists identified the slowly moving mantle flow, which rises beneath the eastern Atlantic Ocean and then spreads out eastward underneath Europe and Africa. At its widest, the current measures about 1,500 by 2,500 miles (2,500by 4,000 kilometers), scientists from Germany and the United States report in the journal Nature. This doesn't fit too well with the conventional vision of Earth's interior. Many geophysicists believe that mantle upwellings take the form of relatively narrow plumes, about 120 to 250 miles wide (200 to 400 km). They are thought to resemble the inverted teardrop-shaped blobs of oil in lava lamps. After millions of years of travel, plumes can burn through Earth's crust, forming hot spots like the one that created the Hawaiian Islands.

But studies of volcanic rocks from Italy, the Canary Islands and other widely spaced sites around Europe support the existence of an upwelling sheet, says Kaj Hoernle, a geochemist at the GEOMAR Research Center in Kiel, Germany. Hoernle and two colleagues found that the volcanic rocks shared important chemical similarities. The widely spaced volcanoes that erupted these rocks may have all drawn on the same deep fuel source, the scientists suggest.

Besides challenging theories on mantle circulation, the existence of the mantle sheet may explain why parts of Earth's crust extending from the western Mediterranean to northwest Germany are thinning and spreading apart. Much of this area, researchers explain, lies over what seems to be the hottest zone of the mantle current. The heat from that flow may be cooking the bottom of the crust, causing it to rift apart.

The outstanding question is whether this mantle sheet is any more real than the infamous Godzilla. Seismologist John VanDecar of the Carnegie Institution in Washington, D.C., points out that seismographic stations, which are all land- based, can't make out mantle structures under oceans as well as those underneath dry land. So although the geochemical evidence for the mantle sheet is compelling, says VanDecar, careful tests will have to be performed on the seismic imaging data to prove the mantle structure actually exists.

PHOTO (COLOR): A current of hot mantle rock (shown here in yellow) may rise beneath Europe and North Africa, fueling volcanoes and causing parts of Central Europe and the western Mediterranean to rift apart.

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By Larry O'Hanlon

Copyright of Earth is the property of Kalmbach Publishing Co.. Copyright of PUBLICATION is the property of PUBLISHER. The copyright in an individual article may be maintained by the author in certain cases. Content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Source: Earth, Aug95, Vol. 4 Issue 4, p16, 2p Item: 9507122910

Earth hums, but we can't hear tune

By Tom Spears

Earth actually hums.The planet vibrates at a very low frequency -- too low for our ears to pick up, but enough that geologists get an annoying background noise on their sensitive instruments.

Two California scientists suggest a reason. They tracked down where and when the hum is loudest, and decided it's the result of storms whipping up the oceans, and transferring that powerful energy to the Earth's crust. And no, they can't turn down the volume.

The hum has been known for years. Like all sounds, it's caused by a vibration. But Earth's hum is a vibration with a frequency of less than once per minute, like a very slow pendulum. That makes the sound incredibly low.

Still, geophysicists who measure slow movements of the Earth's crust can pick up sounds this low. Two of them went looking for the source of the hum, using seismic stations in California and Japan.

Junkee Rhie and Barbara Romanowicz of the University of California at Berkeley figured the hum had to involve a very large amount of energy. But strangely, the hum often reaches its loudest on days with no earthquakes. So it can't be produced by Earth's plates rubbing against each other.

The type of vibration meant the source had to be close to Earth's surface.

They found the main sources for humming are found in two times and places: The North Pacific in winter, and the South Atlantic during its winter (Canada's summer).

These are stormy times in both places.

"This suggests that the hum is a product of the interaction between the atmosphere, ocean and sea floor, probably by the conversion of storm energies to sea-floor vibrations," the two conclude in today's issue of the journal Nature. In other words, winds whip up water, and ocean waves pass on their energy to the ocean floor.

The North Atlantic is as stormy in winter as the North Pacific, but it doesn't seem to create a hum, the scientists found -- possibly because the Atlantic Ocean floor is a different shape and doesn't pick up ocean vibrations as well.

If it isn't one vibration, it's another. Something in our planet is always shaking, and if there isn't this kind of hum there are other vibrations and other causes, said John Cassidy of the Geological Survey of Canada.

There are earthquakes. "If you get a really big earthquake, like a magnitude 8, it literally sets the whole Earth ringing like a bell," he said.

And there's a kind of commotion called torsion, caused by the stress of one part of Earth rotating one way and another part being a little out of sync.

The hum doesn't bother the type of seismic instruments used in Canada, Cassidy said. Its frequency is too low.

-- CanWest News Service Copyright of Winnipeg Free Press (MB) is the property of Winnipeg Free Press (MB). Copyright of PUBLICATION is the property of PUBLISHER. The copyright in an individual article may be maintained by the author in certain cases. Content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Source: Winnipeg Free Press (MB), Sep 30, 2004, pa19 Item: 7BS3891890972

EARTHQUAKES

Earthquakes may be so weak that they are hardly felt, or strong enough to do great damage. There are thousands of earthquakes each year, but most are too small to be noticed. About 1 in 5 can be felt, and about 1 in 500 causes damage.

WHAT CAUSES EARTHQUAKES? The Earth's outer layer, its crust, is divided into huge pieces called plates. These plates, made of rock, are constantly moving--away from each other, toward each other, or past each other. A crack in Earth's crust between two plates is called a fault. Many earthquakes occur along faults where two plates collide as they move toward each other or grind together as they move past each other. Earthquakes along the San Andreas Fault in California are caused by the grinding of two plates.

MEASURING EARTHQUAKES

The Richter scale goes from 0 to more than 8. These numbers indicate the strength of an earthquake. Each number means the quake releases about 30 times more energy than the number below it. An earthquake measuring 6 on the scale is about 30 times stronger than one measuring 5 and 900 times stronger than one measuring 4. Earthquakes that are 4 or above are considered major. (The damage and injuries caused by a quake also depend on other things, such as whether the area is heavily populated and built up.)

The strength of an earthquake, its magnitude, is registered on an instrument called a seismograph and is given a number on a scale called the Richter scale.

Here is a list of different magnitudes of earthquakes and their effects.

Magnitude Effects 0-2: Earthquake is recorded by instruments but is not felt by people. 2-3: Earthquake is felt slightly by a few people. 3-4: People feel tremors. Hanging objects like ceiling lights swing. 4-5: Earthquake causes some damage; walls crack; dishes and windows may break. 5-6: Furniture moves; earthquake seriously damages weak buildings. 6-7: Furniture may overturn; strong buildings are damaged; walls and buildings may collapse. 7-8: Many buildings are destroyed; underground pipes break; wide cracks appear in the ground. Above 8: Total devastation, including buildings and bridges; ground wavy.