Solomon Islands earthquake sheds light on enhanced tsunami risk

This is a cartoon of the tectonic plates in the Solomon Islands area showing subduction beneath the Pacific plate. The Pacific plate is not shown. -  Kevin Furlong, Penn State
This is a cartoon of the tectonic plates in the Solomon Islands area showing subduction beneath the Pacific plate. The Pacific plate is not shown. – Kevin Furlong, Penn State

The 2007 Solomon Island earthquake may point to previously unknown increased earthquake and tsunami risks because of the unusual tectonic plate geography and the sudden change in direction of the earthquake, according to geoscientists.

On April 1, 2007, a tsunami-generating earthquake of magnitude 8.1 occurred East of Papua New Guinea off the coast of the Solomon Islands. The subsequent tsunami killed about 52 people, destroyed much property and was larger than expected.

“This area has some of the fastest moving plates on Earth,” said Kevin P. Furlong, professor of geoscience, Penn State. “It also has some of the youngest oceanic crust subducting anywhere.”

Subduction occurs when one tectonic plate moves beneath another plate. In this area, there are actually three plates involved, two of them subducting beneath the third while sliding past each other. The Australia Plate and the Solomon Sea/Woodlark Basin Plate are both moving beneath the Pacific Plate. At the same time, the Australia and Solomon Sea/Woodlark Basin Plates are sliding past each other. The Australia Plate moves beneath the Pacific Plate at about 4 inches a year and the Solomon Sea Plate moves beneath the Pacific Plate at about 5.5 inches per year. As if this were not complicated enough, the Australia and Solomon Sea plates are also moving in slightly different directions.

The researchers who include Furlong; Thorne Lay, professor of Earth and planetary sciences, University of California, Santa Cruz, and Charles J. Ammon, professor of geoscience, Penn State, were intrigued by the occurrence of a great earthquake where the three plates meet and investigated further. They report their findings in today’s (Apr. 10) issue of Science.

The researchers found that the earthquake crossed from one plate boundary — the Australia-Pacific boundary — into another — the Solomon/Woodlark-Pacific boundary. The event began in the Australia Plate and moved across into the Solomon Sea Plate and had two centers of energy separated by lower energy areas.

“Normally we think earthquakes should stop at the plate boundaries,” said Furlong

More importantly, when the earthquake moved from one plate to the other, it quickly changed direction, mimicking the different plate motion directions of the plates involved.

“We are confident that the fault slip in the two main locations are different by 30 to 40 degrees,” said Furlong. “I do not know of any other place where we have observed that behavior during an earthquake before, but it most certainly has happened here before.”

The two motion directions during the earthquake caused the Pacific plate to bunch up and uplift. This localized atypical uplift during this earthquake reached a maximum of a couple of yards. This uplift is proposed to be the cause of a local increase in tsunami heights. It may also be what has produced these near-trench islands.

“This event, repeated enough times may be why islands in this area are plentiful,” said Furlong. “They are coral islands, not volcanic ones, and so are created by uplift.”

Another unusual component of this earthquake is the abruptness at which the earthquake’s direction changed. Seismic data indicate that the change occurred in 12.5 miles or less.

Furlong notes, however that the change could have happened in even less distance, but the seismic data are only sensitive enough to recognize changes on that scale.

According to Furlong, seismologists do not expect young sections of the Earths crust to be locations of major earthquakes, so the Solomon Island earthquake was unusual from the beginning. He also believes that similar areas exist or existed.

“Other places along subduction zones had this type of geography in the past and might show up geologically,” said Furlong. “At present there are locations along the margins of Central America and southern South America that could potentially host similar earthquakes.”

A better understanding of earthquakes zones like the Solomon Islands may help residents along other complex plate boundaries to better prepare for localized regions of unusually large uplift and tsunami hazards.

Did a nickel famine trigger the ‘Great Oxidation Event’?

The Earth’s original atmosphere held very little oxygen. This began to change around 2.4 billion years ago when oxygen levels increased dramatically during what scientists call the “Great Oxidation Event.” The cause of this event has puzzled scientists, but researchers writing in Nature* have found indications in ancient sedimentary rocks that it may have been linked to a drop in the level of dissolved nickel in seawater.

“The Great Oxidation Event is what irreversibly changed surface environments on Earth and ultimately made advanced life possible,” says research team member Dominic Papineau of the Carnegie Institution’s Geophysical Laboratory. “It was a major turning point in the evolution of our planet, and we are getting closer to understanding how it occurred.”

The researchers, led by Kurt Konhauser of the University of Alberta in Edmonton, analyzed the trace element composition of sedimentary rocks known as banded-iron formations, or BIFs, from dozens of different localities around the world, ranging in age from 3,800 to 550 million years. Banded iron formations are unique, water-laid deposits often found in extremely old rock strata that formed before the atmosphere or oceans contained abundant oxygen. As their name implies, they are made of alternating bands of iron and silicate minerals. They also contain minor amounts of nickel and other trace elements.

Nickel exists in today’s oceans in trace amounts, but was up to 400 times more abundant in the Earth’s primordial oceans. Methane-producing microorganisms, called methanogens, thrive in such environments, and the methane they released to the atmosphere might have prevented the buildup of oxygen gas, which would have reacted with the methane to produce carbon dioxide and water. A drop in nickel concentration would have led to a “nickel famine” for the methanogens, who rely on nickel-based enzymes for key metabolic processes. Algae and other organisms that release oxygen during photosynthesis use different enzymes, and so would have been less affected by the nickel famine. As a result, atmospheric methane would have declined, and the conditions for the rise of oxygen would have been set in place.

The researchers found that nickel levels in the BIFs began dropping around 2.7 billion years ago and by 2.5 billion years ago was about half its earlier value. “The timing fits very well. The drop in nickel could have set the stage for the Great Oxidation Event,” says Papineau. “And from what we know about living methanogens, lower levels of nickel would have severely cut back methane production.”

What caused the drop in nickel? The researchers point to geologic changes that were occurring during the interval. During earlier phases of the Earth’s history, while its mantle was extremely hot, lavas from volcanic eruptions would have been relatively high in nickel. Erosion would have washed the nickel into the sea, keeping levels high. But as the mantle cooled, and the chemistry of lavas changed, volcanoes spewed out less nickel, and less would have found its way to the sea.

“The nickel connection was not something anyone had considered before,” says Papineau. “It’s just a trace element in seawater, but our study indicates that it may have had a huge impact on the Earth’s environment and on the history of life.”

Scientists pierce veil of clouds to ‘see’ lightning inside a volcanic plume

Scientists have pierced the veil of clouds around a volcanic plume to 'see' lightning. -  Bretwood Higman
Scientists have pierced the veil of clouds around a volcanic plume to ‘see’ lightning. – Bretwood Higman

Researchers hit the jackpot in late March, when, for the first time, they began recording data on lightning in a volcanic eruption–right from the start of the eruption.

Using a multi-station, ground-based Lightning Mapping Array, the scientists advanced our understanding of electrical activity during a volcanic eruption.

Portable Lightning Mapping Arrays are now set up in several areas of the country, and are becoming increasingly used by meteorologists to issue weather warnings.

The arrays have been deployed at volcanoes only twice before.

Thousands of individual segments of a single lightning stroke can be mapped with the Lightning Mapping Array, and later analyzed to reveal how lightning initiates and spreads through a thunderstorm, or in a volcanic plume.

When Alaska’s Redoubt Volcano started rumbling in January, a team of researchers hurried to set up a series of the arrays.

When the volcano erupted on March 22 and 23, 2009, the arrays returned dramatic information about the electricity created within volcanic plumes, and the resulting lightning.

“For the first time, we had the Lightning Mapping Array on site before the initial eruption,” said scientist Sonja Behnke of New Mexico Tech.

“The data will allow us to better understand the electrical charge structure inside a volcanic plume,” said scientist Ron Thomas of New Mexico Tech. “That should help us learn how the plume is becoming electrified, and how it evolves over time.”

Bradley Smull, program director in the National Science Foundation (NSF)’s Division of Atmospheric Sciences, which funded the research, said the information will give scientists insights into the electrical mechanisms in both plumes above active volcanoes, and in lightning spawned in thunderstorms.

NSF awarded New Mexico Tech a grant to study volcanic lightning in 2007, with the University of Alaska at Fairbanks and the Alaska Volcano Observatory as collaborators.

“With data from the Lightning Mapping Array, new details of volcanic plume lightning will emerge,” Smull said. “The opportunity for stand-alone analysis, and comparisons with last year’s similar observations of Chaiten Volcano in Chile, will tell us much more about this phenomenon.”

Redoubt was “a perfect laboratory,” said physicist Paul Krehbiel of New Mexico Tech. “It erupted on schedule–and gave us two months’ notice.”

Advance warning was critical to the mission.

In late 2008, Redoubt showed initial signs of seismic activity. Volcanologist Steve McNutt and colleagues at the Alaska Volcano Observatory (AVO) started scouting locations for sensors.

Then in March, “this volcano, in the space of a week, had several major eruptions that produced prolific lightning,” Krehbiel said.

The four Lightning Mapping Array stations are located along the east side of Cook Inlet, across from the volcano.

Thomas, Krehbiel, Behnke and McNutt found cooperative people in accessible locations to serve as caretakers for the stations: The northernmost sensor is at a school teacher’s house in Nikiski. The second is at a fire station south of Kenai. A third is at Clam Gulch Lodge. The southernmost and fourth sensor is at a public school in Ninilchik.

In addition to the Lightning Mapping Array, the AVO is gathering data from 11 local seismic stations, two infrasound arrays and two radar stations.

“It’s hard to get the sensors set up before a volcano erupts,” said Thomas. “You plan–and hope you can do something like this once in a lifetime.”

The Redoubt eruptions are not over yet. After quieting down and appearing to go into a dome-building phase, just before sunrise this past Saturday the volcano blew its top in the biggest eruption so far.

“The lightning activity was as strong or stronger than we have seen in large midwestern thunderstorms,” Krehbiel said. “The radio frequency noise was so strong and continuous that people living in the area would not have been able to watch broadcast VHF television stations.”

Dust plays larger than expected role in determining Atlantic temperature

The recent warming trend in the Atlantic Ocean is largely due to reductions in airborne dust and volcanic emissions during the past 30 years, according to a new study.

Since 1980, the tropical North Atlantic has been warming by an average of a quarter-degree Celsius (a half-degree Fahrenheit) per decade. Though this number sounds small, it can translate to big impacts on hurricanes, which thrive on warmer water, says Amato Evan, a researcher with the University of Wisconsin-Madison’s Cooperative Institute for Meteorological Satellite Studies and lead author of the new study. For example, the ocean temperature difference between 1994, a quiet hurricane year, and 2005’s record-breaking year of storms, was just one degree Fahrenheit.

More than two-thirds of this upward trend in recent decades can be attributed to changes in African dust storm and tropical volcano activity during that time, report Evan and his colleagues at UW-Madison and the National Oceanic and Atmospheric Administration in a new paper. Their findings will appear in an upcoming issue of the journal Science and publish online March 26.

Evan and his colleagues have previously shown that African dust and other airborne particles can suppress hurricane activity by reducing how much sunlight reaches the ocean and keeping the sea surface cool. Dusty years predict mild hurricane seasons, while years with low dust activity – including 2004 and 2005 – have been linked to stronger and more frequent storms.

In the new study, they combined satellite data of dust and other particles with existing climate models to evaluate the effect on ocean temperature. They calculated how much of the Atlantic warming observed during the last 26 years can be accounted for by concurrent changes in African dust storms and tropical volcanic activity, primarily the eruptions of El Chichón in Mexico in 1982 and Mount Pinatubo in the Philippines in 1991.

In fact, it is a surprisingly large amount, Evan says. “A lot of this upward trend in the long-term pattern can be explained just by dust storms and volcanoes,” he says. “About 70 percent of it is just being forced by the combination of dust and volcanoes, and about a quarter of it is just from the dust storms themselves.”

The result suggests that only about 30 percent of the observed Atlantic temperature increases are due to other factors, such as a warming climate. While not discounting the importance of global warming, Evan says this adjustment brings the estimate of global warming impact on Atlantic more into line with the smaller degree of ocean warming seen elsewhere, such as the Pacific.

“This makes sense, because we don’t really expect global warming to make the ocean [temperature] increase that fast,” he says.

Volcanoes are naturally unpredictable and thus difficult to include in climate models, Evan says, but newer climate models will need to include dust storms as a factor to accurately predict how ocean temperatures will change.

“We don’t really understand how dust is going to change in these climate projections, and changes in dust could have a really good effect or a really bad effect,” he says.

Satellite research of dust-storm activity is relatively young, and no one yet understands what drives dust variability from year to year. However, the fundamental role of the temperature of the tropical North Atlantic in hurricane formation and intensity means that this element will be critical to developing a better understanding of how the climate and storm patterns may change.

“Volcanoes and dust storms are really important if you want to understand changes over long periods of time,” Evan says. “If they have a huge effect on ocean temperature, they’re likely going to have a huge effect on hurricane variability as well.”

Bent tectonics: How Hawaii was bumped off

More than 80 undersea volcanoes and a multitude of islands are dotted along the Hawaii-Emperor seamount chain like pearls on a necklace. A sharp bend in the middle is the only blemish. The long-standing explanation for this distinctive feature was a change in direction of the Pacific oceanic plate in its migration over a stationary hotspot – an apparently unmoving volcano deep within the earth.


According to the results of an international research group, of which Ludwig-Maximilians-Universität München geophysicist Professor Hans-Peter Bunge was a member, however, the hotspot responsible for the Hawaii-Emperor seamount chain was not fixed. Rather it had been drifting quite distinctly southward. Nearly 50 million years ago, it finally came to rest while the Pacific plate steadily pushed on, the combination of which resulted in the prominent bend. The movements of hotspots are determined by circulations in the earth’s mantel. “These processes are not of mere academic interest,” Bunge emphasizes. “Mantel circulation models help us understand the forces that act on tectonic plates. This in turn is essential for estimating the magnitude and evolution of stresses on the largest tectonic fault lines, that is the sources of many major earthquakes.”

The characteristic bend in the trail of the 5000 kilometer long Hawaii-Emperor seamount chain is one of the most striking topographical features of the earth, and is an identifying feature in representations of the Pacific Ocean floor. For a long time, textbooks have explained the creation of the Hawaii-Emperor chain as an 80 million year-long migration of the Pacific oceanic plate over a stationary hotspot. Hotspots are volcanoes rooted deep within the bowels of the earth, from which hot material is constantly pushing its way up to the surface. According to this now obsolete scenario, the bend would have come about as the Pacific plate abruptly changed direction.

In the past 30 years, geophysicists had also depended on the apparently unchanging locations of hotspots in the earth’s mantel in their definition of a global reference for plate tectonics. More recent investigations, however, suggest that hotspots are less stationary than so far assumed. An international research group, of which Professor Hans-Peter Bunge of the LMU Munich Department of Earth and Environmental Sciences was a member, took a closer look at certain evidence pointing towards substantial inherent motion of the underground volcanoes, and has now confirmed this evidence.

“Paleomagnetic observations suggest that the bend in the Hawaii-Emperor chain is not the result of a change in the relative motion of the Pacific plate,” Bunge states. “On the contrary, it seems the hotspot had been drifting rapidly in a southward direction between 80 and 40 million years ago before it came to a complete halt.” If the trail of the Hawaiian hotspot is corrected to include this drift, the result implies a largely constant movement of the Pacific plate over the last 80 million years. The bend ultimately came about as the hotspot started to slow down.

The driving force behind the migration of the hotspot is the circulation of material under the surface of our planet. “The earth’s interior is in constant motion,” reports Bunge. “Over geological timescales, this motion compares to the weather patterns in our atmosphere. These patterns can easily lead to a change in position of hotspots. Numerical simulations of this global circulation in the earth’s mantel allow us to retrace these motions in unprecedented detail.”

The new data will now be entered into the mantel circulation models presently used. These calculations help explain the driving and resisting forces acting on tectonic plates. “And we need to understand these forces because they are essential for estimating the magnitude and evolution of stresses on the major tectonic fault lines – that is, the sources of many major earthquakes on our planet,” says Bunge. The findings to come from these models will allow scientists to improve their computer models by checking their calculations against observations.

Simulations and ancient magnetism suggest mantle plumes may bend deep beneath Earth’s crust

Computer simulations, paleomagnetism and plate motion histories described in today’s issue of Science reveal how hotspots, centers of erupting magma that sit atop columns of hot mantle that were once thought to remain firmly fixed in place, in fact move beneath Earth’s crust.

Scientists believe mantle plumes are responsible for some of the Earth’s most dramatic geological features, such as the Hawaiian islands and Yellowstone National Park. Some plumes may have shallow sources, but a few, such as the one beneath Hawaii, appear to be rooted in the deepest mantle, near Earth’s core.

Such deep plumes have long been thought to be so immobile that the motions of continental and oceanic plates were measured against them, but University of Rochester geophysicist John Tarduno and his colleagues at Ludwig-Maximilians, Münster, and Stanford universities have combined magnetic evidence from the Pacific sea floor with computer modeling to show how the plume beneath Hawaii likely bent-its root barely moving while its top moved nearly 1,000 miles across the underside of the Pacific Ocean.

“In 2003, we showed that the hotspot-the plume-that created the Hawaiian chain of islands must have moved. We suggested that mantle motion was involved, but the cause of the change in motion remained a mystery,” says Tarduno.

Tarduno cites five possible mechanisms in Science, but one in particular, he says, stands out as a likely explanation for the way the Hawaiian chain of islands and seamounts formed. “We know from theory and from models, including work by Ulrich Hansen and Norm Sleep, that a plume can move slightly near its base, potentially contributing to motion of the Hawaiian hotspot and hotspots elsewhere,” says Tarduno. “But a key observation came from a numerical simulation resulting from Hans-Peter Bunge’s models, which show how the upper end of the plume, starting at 1500 depth, can drift like a candle flame drawn toward a draft.”

The draft in this case, he says, is an ancient oceanic ridge in the Pacific where the seafloor spreads, allowing magma to bubble up through the ocean crust. The ancient ridge is now lost to subduction, but its past presence is recorded by a few magnetic lineations in oceanic crust south of the Bering Sea. The ridge was active around 80 million years ago but extinguished completely by 47 million years ago. Those dates correspond very closely with the motion history Tarduno detected in the Hawaiian hotspot.

In 2001, Tarduno and an international team spent two months aboard the ocean drilling ship JOIDES Resolution, retrieving samples of rock from the Emperor-Hawaiian seamount chain miles beneath the sea’s surface. The team started at the northern end of the chain, near Japan, braving cold, foggy days and dodging the occasional typhoon to pull up several long cores of rock as they worked their way south. Using a highly sensitive magnetic device called a SQUID (Superconducting Quantum Interference Device), Tarduno’s team discovered that the magnetism of the cores did not fit with the conventional wisdom of fixed hotspots.

The magnetization of the lavas recovered from the northern end of the Emperor-Hawaiian chain suggested these rocks were formed much farther north than the current hotspot, which is forming Hawaii today. As magma forms, magnetite, a magnetically sensitive mineral, records the Earth’s magnetic field just like a compass. As the magma cools and becomes solid rock, the “compass” orientation is locked in place, preserving a precise record of the latitude of origin.

If the Hawaiian hot spot had always been fixed at its current location of 19 degrees north, then all the rocks of the entire chain should have formed and cooled there, preserving the magnetic signature of 19 degrees even as the Pacific plate dragged the new stones north-westward. Tarduno’s team, however, found that the more northern their samples, the higher the samples’ latitude. The northern-most lavas they recovered were formed at over 30 degrees north about 80 million years ago, nearly a thousand miles from where the hot spot currently lies.

“The only way to account for these findings is if the hotspot itself was moving south,” says Tarduno. His magnetic readings leveled off at a latitude of nearly 19 degrees, suggesting that the magma plume ceased moving in the area it resides in today.

In addition to the “draft” created by the upwelling of magma into the paleo-ridge, Tarduno says that theory and computer simulations suggest that the most a plume can bend under such conditions would result in about 1,000 miles of movement across the crust-matching what he sees as the distance between the start and stop points of the Hawaiian hotspot. He points out that the bending of a mantle plume helps reconcile the evidence of mobile hotspots on the Earth’s crust with the theories that suggest plumes originate in the deepest mantle where high viscosity limits rapid motion. He points out that the plume-ridge capture mechanism may also help explain seemingly anomalous volcanic features on the seafloor, and help geoscientists to use ancient volcanic tracks to understand the past flow of Earth mantle.

Straw bale house survives violent shaking at earthquake lab

It huffed and puffed, but the 82-ton-force, earthquake-simulation shake table could not knock down the straw house designed and built by University of Nevada, Reno alumna and civil engineer Darcey Donovan. The full-scale, 14-by-14-foot straw house, complete with gravel foundation and clay plaster walls, the way she builds them in Pakistan, was subjected to 200 percent more acceleration/shaking than was recorded at the 1994 Northridge, Calif. earthquake, the largest measured ground acceleration in the world. After a series of seven increasingly forceful tests, in the final powerful test the house shook and swayed violently, cracked at the seams and sent out a small cloud of dust and straw and remained standing. -  Mike Wolterbeek, University of Nevada, Reno
It huffed and puffed, but the 82-ton-force, earthquake-simulation shake table could not knock down the straw house designed and built by University of Nevada, Reno alumna and civil engineer Darcey Donovan. The full-scale, 14-by-14-foot straw house, complete with gravel foundation and clay plaster walls, the way she builds them in Pakistan, was subjected to 200 percent more acceleration/shaking than was recorded at the 1994 Northridge, Calif. earthquake, the largest measured ground acceleration in the world. After a series of seven increasingly forceful tests, in the final powerful test the house shook and swayed violently, cracked at the seams and sent out a small cloud of dust and straw and remained standing. – Mike Wolterbeek, University of Nevada, Reno

It huffed and puffed, but the 82-ton-force, earthquake-simulation shake table could not knock down the straw house designed and built by University of Nevada, Reno alumna and civil engineer Darcey Donovan.

The full-scale, 14-by-14-foot straw house, complete with gravel foundation and clay plaster walls, the way she builds them in Pakistan, was subjected to 200 percent more acceleration/shaking than was recorded at the 1994 Northridge, Calif. earthquake, the largest measured ground acceleration in the world. After a series of seven increasingly forceful tests, in the final powerful test the house shook and swayed violently, cracked at the seams and sent out a small cloud of dust and straw…and remained standing.

Donovan oversaw the successful series of seismic tests run March 27 at the University’s world-renowned Large-Scale Structures Laboratory. She was testing her innovative design for straw bale houses she has been building since 2006 throughout the northwest frontier provinces of Pakistan, in the foothills of the Himalayas between Pakistani tribal areas and Kashmir. Her design uses bales as structural and load-bearing components rather than just insulation as in other straw-bale designs.

“We’re very pleased with the results,” said Donovan, founder/CEO of the non-profit Pakistan Straw Bale and Appropriate Building (PAKSBAB) organization. “The house performed exceptionally well and survived 0.82g (0.82 times the acceleration of gravity) and twice the acceleration of the Northridge quake. The Geological Survey of Pakistan estimates the 2005 Kashmir earthquake to have had peak ground accelerations in the range of 0.3 to 0.6g.

Most people were killed and injured in that October 2005 earthquake as they slept when their poorly built houses collapsed on top of them. The magnitude 7.6 earthquake killed 100,000 people and left 3.3 million homeless or living in tents.

“Our goal is to get the largest number of poor people into earthquake-safe homes. We want to make it as affordable as possible so they build a safe home. We want to save lives.”

“Straw bale houses are used around the world, but those have posts and beams for support and rely on energy-intensive materials, skilled labor and complex machinery, making it unaffordable for the poor,” Donovan said. “In our design, the straw bales are the support, and not just for insulation. Our design is half the cost of conventional earthquake-safe construction in Pakistan. The materials we use – clay soil, straw and gravel – are readily available; and we utilize unskilled labor in the construction.

“We build a small, steel compression box, pack it with straw, which is readily available from the Punjab District, literally stomp on it to compress it, add a little more, stomp on it a little more, and then finally use standard farm-type hand jacks to do the final compressing of the bales,” Donovan said.

The site-fabricated bales are not as wide as those used in a typical straw bale building, and the fishing-net reinforcement and gravel-bag foundation are nonconventional.

“We fill old vegetable sacks with gravel, like sandbags, for the foundation. The bags are fully encased, or boxed, in a mortar made from clay soil and cement. It’s as low-tech as possible using indigenous, affordable materials,” she said. The earthquake-safe buildings are 80 percent more energy efficient than modern conventional buildings at 50 percent of the cost. Her group also trains local residents how to build the homes.

“Our system is different than anything ever tested,” she said. “We’re doing seismic research on the house to have data to show its structural integrity.” While there are no building codes in the region, Donovan and the organization she founded, PAKSBAB, are pursuing an endorsement from Pakistan’s newly formed Earthquake Reconstruction and Rehabilitation Authority.

Scientists will analyze the seismic-testing results, and Donovan will write a detailed report and seismic design and construction recommendations to be published in the Earthquake Engineering Research Institute’s World Housing Encyclopedia.

Donovan has been a practicing engineer since 1986. She has a bachelor of science degree in mechanical engineering from Stanford University, a master of science in civil engineering from the University of Nevada, Reno, and is a licensed Professional Civil Engineer.

The research was conducted at the Network for Earthquake Engineering Simulation Consortium, Inc. (NEES) shake-table site at the University of Nevada, Reno as a NEES Management, Operations and Maintenance award shared-use project.

“I am extremely grateful to EERI, NEES and UNR for their generous support, and to all the hardworking volunteers who dedicated countless hours to this project, Donovan said.

Ice-free Arctic summers likely sooner than expected

Summers in the Arctic may be ice-free in as few as 30 years, not at the end of the century as previously expected. The updated forecast is the result of a new analysis of computer models coupled with the most recent summer ice measurements.

“The Arctic is changing faster than anticipated,” said James Overland, an oceanographer at NOAA’s Pacific Marine Environmental Laboratory and co-author of the study, which will appear April 3 in Geophysical Research Letters. “It’s a combination of natural variability, along with warmer air and sea conditions caused by increased greenhouse gases.”

Overland and his co-author, Muyin Wang, a University of Washington research scientist with the Joint Institute for the Study of the Atmosphere and Ocean in Seattle, analyzed projections from six computer models, including three with sophisticated sea ice physics capabilities. That data was then combined with observations of summer sea ice loss in 2007 and 2008.

The area covered by summer sea ice is expected to decline from its current 4.6 million square kilometers (about 2.8 million square miles) to about 1 million square kilometers (about 620,000 square miles) – a loss approximately four-fifths the size of the continental U.S. Much of the sea ice would remain in the area north of Canada and Greenland and decrease between Alaska and Russia in the Pacific Arctic.

“The Arctic is often called the ‘Earth’s refrigerator’ because the sea ice helps cool the planet by reflecting the sun’s radiation back into space,” said Wang. “With less ice, the sun’s warmth is instead absorbed by the open water, contributing to warmer temperatures in the water and the air.”

Technique measures heat transport in the Earth’s crust

Putting a new spin on an old technique, Anne M. Hofmeister, Ph.D., research professor of earth and planetary sciences at Washington University in St. Louis, has revolutionized scientists’ understanding of heat transport in the Earth’s crust, the outermost solid shell of our planet.

Temperature is an important driver of many geological processes, including the generation of magmas (molten rocks) in the deepest parts of the Earth’s crust, about 30-40 kilometers below the surface. Yet, until recently, temperatures deep inside the Earth’s crust were uncertain, mainly because of difficulties associated with measuring thermal conductivity, or how much heat is flowing through the rocks that compose the crust.

In conventional methods of measuring thermal conductivity, measurement errors arise as the temperature of a rock nears its melting point. At such high temperatures, heat is not just transported from atom to atom by vibrations, but also by radiation (light). Since conventional methods cannot separate heat flow carried by vibrations from that associated with radiation, most measurements of how efficiently rocks transport heat at high temperatures have been overestimated. Because of this experimental uncertainty, scientists have assumed rock conductivity to be constant throughout the crust in order to make advances in models describing Earth’s geological behavior.

Using an industrial laser that is typically used for steel welding, Hofmeister was able to circumvent the problems that plagued the older methods. Her facility at WUSTL is the first in the world to employ such a laser for geoscience research.

Her technique, laser-flash analysis, provides much more accurate data on heat transport through rocks than conventional methods. In laser-flash analysis, a rock sample is held at a given temperature and then subjected to a laser pulse of heat, allowing Hofmeister to measure the time it takes for the heat to go from one end of the sample to the other. This measurement of
thermal diffusivity, or how fast heat flows through matter, is another way to describe the thermal conductivity of a rock. Since measuring heat transport in the crust itself is impossible, Hofmeister used the laser to measure heat transport in individual rock samples at various temperatures and then averaged across samples to represent the dynamics of the crust. In collaboration with researchers from the University of Missouri, Columbia, Hofmeister applied her findings to explain geological phenomena observed in the environment.

The results, published in Nature on March 19, 2009, suggest that rock conductivity is not constant as was previously assumed, but instead varies strongly with temperature. Hofmeister explains, “Our analysis shows that rocks are more efficient at conducting heat at low temperatures than was previously thought and less efficient at high temperatures. The process of moving heat around really depends on the temperature of the rocks.”

Hofmeister and her collaborators found that the conductivity of rocks in the lower crust, where the external temperature is very high, is much lower — by as much as 50 per cent — than was predicted by conventional methods. These results also suggest that the lower crust may be much hotter than scientists previously recognized. Since rocks become better insulators and poorer conductors at high temperatures, the lower crust acts like a blanket over the heat-generating mantle, the layer underlying the crust.

Magma machine

The observation that the lower crust is a good thermal insulator has broad implications for scientists’ understanding of fundamental geological processes such as magma production.

Hofmeister explains, “The new methods change our understanding of how heat is transported in geological environments. This pertains to where you find magmas, where you cook metamorphic rock, and where lavas form on ocean ridges.”

She and her colleagues used the new temperature-dependent data to inform computer models that predict the consequences of burying and heating up rocks during mountain belt formation, as occurs in the present-day Himalayas. While prior models relied upon extraordinary processes such as high levels of radioactivity to explain melting of the crust in the Himalayas, Hofmeister and her collaborators’ work suggests that the thermal properties of the rocks themselves might be sufficient to generate magmas.

In particular, they find that the strain heating, or friction, caused by mountain belt formation can trigger crustal melting. Because the lower crust is such a good thermal insulator, strain heating is much faster, more efficient, and more self-perpetuating than previously recognized.

“The melt is more insulating than the rock,” explains Hofmeister, “Once you get rocks melting, the thermal diffusivity goes down, which makes it harder to cool the rocks. They stay hot longer and there’s the potential for more melting.”

According to Hofmeister, the Himalaya situation described in the study is probably not unique. Because heat transport is such an important driver, many models of Earth’s geological behavior will need to be revisited in light of Hofmeister and her collaborators’ findings.

These advances bring Hofmeister much closer to accomplishing what she describes as her life-long career objective. “The goal for most of my career has been to determine the temperature inside the earth. It’s the time dependence, how long it takes heat to flow through rocks, that is going to tell us how hot the interior is,” she says.

According to Hofmeister, understanding the temperature of the Earth’s interior is the first step towards understanding the thermal evolution of the earth.

More than 500 seismologists to meet April 8-10 in Monterey, Calif.

Seismologists from around the world will gather at the 2009 Annual Meeting of the Seismological Society of America (SSA). Featuring more than 600 presentations by leading seismologists, the meeting’s special sessions will include a focus on:

  • Central California Coast Seismic Hazard
  • Loma Prieta earthquake, 20 years later
  • New imaging technology that offers fresh data about California faults
  • Observations about the crust beneath the U.S. from USArray

To register or receive a more detailed media tipsheet about selected presentations (available April 1, 2009), please contact Nan Broadbent at nan0604@msn.com or 408-431-9885.

What:Seismological Society of America
2009 SSA Annual Meeting

When:April 8-10, 2009

Where:Portola Hotel & Spa and adjoining Conference Center
Monterey, California