‘Webcam’ from Space: Envisat observing Wilkins Ice Shelf

In light of recent developments that threaten to lead to the break-up of the Wilkins Ice Shelf, ESA is making daily satellite images of the ice shelf available to the public via the ‘Webcam’ from Space web page in order to monitor the developments as they occur.

The Wilkins Ice Shelf, a broad plate of floating ice off the coast of the Antarctic Peninsula, has undergone many changes in 2008. Due to the warming in the Antarctic spring (late November), newly formed rifts were discovered that scientists predict could lead to the opening of the ice bridge that connects the ice shelf to two islands, Charcot and Latady.
If the ice bridge were to open, it could put the entire ice shelf at risk of disintegrating.

ESA’s Envisat acquires images of the ice shelf daily with its Advanced Synthetic Aperture Radar (ASAR) instrument. These images are updated automatically on the Wilkins ‘Webcam’ from Space web page and placed in an animation to allow visitors to spot changes between acquisitions. Individual images can also be viewed in the image archive.

Team first to record key event that breaks continents apart

Purdue University graduate student Sarah D. Stamps and Tanzanian scientist Elifuraha Saria install a Global Positioning System instrument in the Natron area of Tanzania. The Ol Doinyo Lenga volcano is visible in the background. Global Positioning Systems were used by a Purdue-led team to capture the first dyking event ever recorded within the Earth's continental crust. -  Photo courtesy of Eric Calais
Purdue University graduate student Sarah D. Stamps and Tanzanian scientist Elifuraha Saria install a Global Positioning System instrument in the Natron area of Tanzania. The Ol Doinyo Lenga volcano is visible in the background. Global Positioning Systems were used by a Purdue-led team to capture the first dyking event ever recorded within the Earth’s continental crust. – Photo courtesy of Eric Calais

Researchers have captured for the first time a geological event considered key in shaping the Earth’s landscape.

An international research team led by Eric Calais, a Purdue University professor of geophysics, was able to measure ground displacements as two tectonic plates in Africa moved apart and molten rock pushed its way toward the surface during the first so-called “dyking event” ever recorded within the planet’s continental crust.

The event left a wall of magma 6 miles long and 5 feet wide wedged between the two plates. A paper detailing the event will be published Wednesday (Dec. 11) in Nature.

Dyking events have been reported in the thin oceanic crust but had never been directly observed and quantified in the thicker areas of the planet’s shell, Calais said.

“Such dyking events had been included in theories, but researchers had never before been in the right place at the right time with the right equipment to record them,” Calais said. “The event was preceded by a slow slipping of the tectonic plates along a fault line. This also had not been seen before. Faults usually slip suddenly, which produces earthquakes, but this was a very seismically quiet course of events that lasted about one week.”

The existence of these events provides a key element of how the Earth’s rigid outer shell – the lithosphere – breaks apart and moves. The known forces pushing and pulling on continents are not powerful enough to break them apart. However, repeated dyking events could weaken the lithosphere severalfold, allowing it to shift and break under far less force, Calais said.

“To break a continent apart, one needs to overcome the strength of the Earth’s lithosphere,” he said. “But when we calculate the forces available from plate tectonics, we find that they are not large enough to do the job. We know that continents break apart and have done so repeatedly in the geological past. So, how can it happen? One way is to add a little push to the system, and this is exactly what dyke intrusions do.”

During a dyke intrusion, magma held in deep reservoirs breaks through surrounding rock and rises toward the surface, forcing the two plates apart, and, over time, weakening the lithosphere by transferring heat to the surrounding rocks. The magma fills and widens cracks and fractures as it rises. The end result is a vertical wall, or dyke, of magma that has pushed the Earth’s crust apart, he said.

“Eventually, if these events occur over and over again for millions of years, an ocean will form between the two plates,” he said. “So, today in Tanzania, we are really witnessing the earliest stages of ocean formation.”

Calais and his collaborators captured this event in Tanzania’s Lake Natron basin during the summer of 2007. The basin lies near the southern tip of the eastern branch of the East African Rift, the area where the Somalia and Nubia tectonic plates are moving apart.

Reports of a series of moderate earthquakes from northern Tanzania felt all the way to Nairobi in Kenya caught the team’s attention. French collaborators had installed seismographs in the vicinity of the Natron basin a few months before the event and recorded more than 600 small earthquakes in two weeks, pinpointing the center of the tectonic activity. Tanzanian researchers were able to collect Global Positioning System (GPS) measurements in the Natron area. Calais compared these measurements with those taken earlier to determine the amount of displacement of the Earth’s surface. But these displacements did not match what was expected from the earthquakes.

“The displacement was much too large given the small size of the earthquakes, which was the first lead that something unusual was happening,” Calais said. “Soon after these earthquakes, one of the volcanoes in the area entered an explosive eruptive stage, which indicated that magma was involved. So we had an idea this might be a dyking event.”

He then worked with colleagues in Luxembourg to obtain radar interferometry (InSAR) data, which provided a detailed picture of ground movements. A team of led by Belgium scientists went to the area for a field check and mapped 13 miles of open fissures that corresponded well with the observations from InSAR data.

“Once we had all of the measurements, in particular the InSAR data, we knew that the combined dataset could only be explained by the injection of a dyke,” Calais said. “If we had only the GPS data and/or seismic activity data, this would have been difficult to prove. We needed all of these methods to really understand what was happening.”

A dyking event is mostly an aseismic process, meaning it does not create large earthquakes or release a lot of ground-shaking energy. It would be easy to miss such an occurrence without some of the advanced geodetic measurement technology available today, he said.

“When you look at events like this with only one measurement tool, you are half blind,” Calais said. “You are missing a lot of what the planet is telling us. Sometimes it whispers instead of shouting.”

It is possible that there have been several dyking events on the East African Rift within the past few decades, he said.

“If there is evidence that these events have been happening within recent time, there is no reason not to believe that they have been happening for several million years,” Calais said. “This could then be a very important contribution to the dynamics of the East African Rift system.”

Co-authors of the paper include Nicolas d’Oreye and Anneleen Oyen from the National Museum of Natural History in Luxembourg; Julie Albaric, Jacques Déverchère and Julie Perrot from the University of Brest in France; Anne Deschamps from the National Center for Scientific Research in France; Damien Delvaux, Francois Kervyn, Benoit Smets and Christelle Wauthier from the Royal Museum for Central Africa in Belgium; Cynthia Ebinger from the University of Rochester; Richard W. Ferdinand from the University of Dar es Salaam in Tanzania; Athanas S. Macheyeki from the Renard Centre of Marine Geology in Belgium; Elifuraha Saria from Ardhi University in Tanzania; and D. Sarah Stamps from Purdue.

Calais and his collaborators next will watch the surrounding area for the aftermath of this dyking event.

“When a large event like this occurs, the state of stress on the Earth’s upper layers are changed, and we expect several additional events to follow,” Calais said. “Other magma reservoirs may be touched and trigger another dyking event. It will take a while for the system to relax again and get back to its quiet, steady-state, behavior.”

His team also plans to examine the area in more detail to try to discover evidence of past dyking events. This information could illustrate any historical patterns in the incidences of these events and how regularly they occur.

“At stake is a better understanding of geohazards in East African countries, whose fragile economy may easily be disrupted even by seismic or volcanic events of moderate magnitude,” Calais said.

Great Indian Ocean earthquake of 2004 set off tremors in San Andreas fault

In the last few years there has been a growing number of documented cases in which large earthquakes set off unfelt tremors in earthquake faults hundreds, sometimes even thousands, of miles away.

New research shows that the great Indian Ocean earthquake that struck off the Indonesian island of Sumatra on the day after Christmas in 2004 set off such tremors nearly 9,000 miles away in the San Andreas fault at Parkfield, Calif.

“We found that an earthquake that happened halfway around the world could trigger a seismic signal in the San Andreas fault. It is a low-stress event and a new kind of seismic phenomenon,” said Abhijit Ghosh, a University of Washington doctoral student in Earth and space sciences.

“Previous research has shown that this phenomenon, called non-volcanic tremor, was produced in the San Andreas fault in 2002 by the Denali earthquake in Alaska, but seeing this new evidence of tremor triggered by an event as distant as the Sumatra earthquake is really exciting,” he said.

Ghosh is to present the findings next week (Dec. 17) in a poster at the American Geophysical Union annual meeting in San Francisco.

The Indian Ocean earthquake on Dec. 26, 2004, was measured at magnitude 9.2 and generated tsunami waves that killed a quarter-million people. It was not known, however, that an earthquake of even that magnitude could set off non-volcanic tremor so far away.

The San Andreas fault in the Parkfield region is one of the most studied seismic areas in the world. It experiences an earthquake of magnitude 6.0 on an average of every 22 years, so a variety of instruments have been deployed to record the seismic activity.

In this case, the scientists examined data from instruments placed in holes bored in the ground as part of the High-Resolution Seismic Network operated by the University of California, Berkeley, as well as information gathered by the Northern California Seismic Network operated by the U.S. Geological Survey.

Signals corresponding with non-volcanic tremor at precisely the time that seismic waves from the Indian Ocean earthquake were passing the Parkfield area were recorded on a number of instruments as far as 125 miles apart.

“It’s fairly obvious. There’s no question of this tremor being triggered by the seismic waves from Sumatra,” Ghosh said.

Scientists have pondered whether non-volcanic tremor is related to actual slippage within an earthquake fault or is caused by the flow of fluids below the Earth’s surface. Recent research supports the idea that tremor is caused by fault slippage.

“If the fault is slipping from tremor in one place, it means stress is building up elsewhere on the fault, and that could bring the other area a little closer to a big earthquake,” Ghosh said.

Monitoring tremor could help to estimate how much stress has built up within a particular fault.

“If the fault is closer to failure, then even a small amount of added stress likely can produce tremor,” he said. “If the fault is already at low stress, then even high-energy waves probably won’t produce tremor.”

The work adds to the understanding of non-volcanic tremor and what role it might play in releasing or shifting stress within an earthquake-producing fault.

“Our single-biggest finding is that very small stress can trigger tremor,” Ghosh said. “Finding tremor can help to track evolution of stress in the fault over space and time, and therefore could have significant implications in seismic hazard analysis.”

Southern Ocean resistant to changing winds

Intensifying winds in the Southern Ocean have had little influence on the strength of the Southern Ocean circulation and therefore its ability to absorb carbon dioxide from the atmosphere, according to a study published in Nature Geoscience.

The Southern Ocean slows the rate of greenhouse warming by removing carbon dioxide from the atmosphere and storing it in the ocean. But previous studies raised the alarm by suggesting the Southern Ocean carbon sink is now ‘saturated’ and no longer able to keep pace with increasing concentrations of carbon dioxide in the atmosphere.

The new study suggests that Southern Ocean currents, and therefore the Southern Ocean’s ability to soak up carbon dioxide, have not changed in recent decades, despite a large increase in winds.

A team of German and Australian scientists compared new ocean measurements from a global network of ocean robots with historical data from ships to determine if the Southern Ocean was changing. The study was led by Professor Claus B?ing from the Institute of Marine Research (IFM-GEOMAR), Kiel.

Co-author, CSIRO’s Dr Steve Rintoul, says the Southern Ocean was found to have become warmer and fresher since the 1960s – a pattern consistent with the ‘fingerprint’ of climate change caused by carbon emissions from human activity.

“But, counter to our expectations, other aspects of the Southern Ocean have not changed despite the increase in winds,” he says. “In particular, we found no evidence of a change in strength of the ocean currents that circle around Antarctica, or in the amount of deep water rising to the surface near Antarctica.”

The fact that the upwelling of deep water has not changed is important. Deep water is very rich in carbon dioxide and so an increase in upwelling tends to transfer carbon dioxide from the ocean to the atmosphere. The low-resolution models used for climate forecasts predict stronger winds, which cause stronger upwelling and therefore less carbon dioxide being stored in the ocean.

“Our results suggest that the small-scale motions of ocean eddies act to balance the stronger winds, with no change in upwelling,” Dr Rintoul says. “Climate models in use today cannot represent these small-scale motions and so over-estimate the response of the Southern Ocean to changes in winds.” Dr Rintoul works through the Antarctic Climate and Ecosystem Cooperative Research Centre (ACECRC) and CSIRO’s Wealth from Oceans Flagship.

Integral to the research was the Australian ocean data archive and the Argo network of ocean profilers. The data provided by the global array of more than 3,100 Argo floats is particularly valuable in remote areas like the sparsely-sampled Southern Ocean.

Cave’s climate clues show ancient empires declined during dry spell

The decline of the Roman and Byzantine Empires in the Eastern Mediterranean more than 1,400 years ago may have been driven by unfavorable climate changes.

Based on chemical signatures in a piece of calcite from a cave near Jerusalem, a team of American and Israeli geologists pieced together a detailed record of the area’s climate from roughly 200 B.C. to 1100 A.D. Their analysis, to be reported in an upcoming issue of the journal Quaternary Research, reveals increasingly dry weather from 100 A.D. to 700 A.D. that coincided with the fall of both Roman and Byzantine rule in the region.

The researchers, led by University of Wisconsin-Madison geology graduate student Ian Orland and professor John Valley, reconstructed the high-resolution climate record based on geochemical analysis of a stalagmite from Soreq Cave, located in the Stalactite Cave Nature Reserve near Jerusalem.

“It looks sort of like tree rings in cross-section. You have many concentric rings and you can analyze across these rings, but instead of looking at the ring widths, we’re looking at the geochemical composition of each ring,” says Orland.

Using oxygen isotope signatures and impurities – such as organic matter flushed into the cave by surface rain – trapped in the layered mineral deposits, Orland determined annual rainfall levels for the years the stalagmite was growing, from approximately 200 B.C. to 1100 A.D.

While cave formations have previously been used as climate indicators, past analyses have relied on relatively crude sampling tools, typically small dental drills, which required averaging across 10 or even 100 years at a time. The current analysis used an advanced ion microprobe in the Wisconsin Secondary-Ion Mass-Spectrometer (Wisc-SIMS) laboratory to sample spots just one-hundredth of a millimeter across. That represents about 100 times sharper detail than previous methods. With such fine resolution, the scientists were able to discriminate weather patterns from individual years and seasons.

Their detailed climate record shows that the Eastern Mediterranean became drier between 100 A.D. and 700 A.D., a time when Roman and Byzantine power in the region waned, including steep drops in precipitation around 100 A.D. and 400 A.D. “Whether this is what weakened the Byzantines or not isn’t known, but it is an interesting correlation,” Valley says. “These things were certainly going on at the time that those historic changes occurred.”

The team is now applying the same techniques to older samples from the same cave. “One period of interest is the last glacial termination, around 19,000 years ago – the most recent period in Earth’s history when the whole globe experienced a warming of 4 to 5 degrees Celsius,” Orland says.

Formations from this period of rapid change may help them better understand how weather patterns respond to quickly warming temperatures.

Soreq Cave – at least 185,000 years old and still active – also offers the hope of creating a high-resolution long-term climate change record to parallel those generated from Greenland and Antarctic ice cores.

“No one knows what happened on the continents? At the poles, the climate might have been quite different,” says Valley. “This is a record of what was going on in a very different part of the world.”

Modern day scourge helped ancient Earth escape a deathly deep freeze

The planet’s present day greenhouse scourge, carbon dioxide, may have played a vital role in helping ancient Earth to escape from complete glaciation, say scientists in a paper published online today.

In their review for Nature Geoscience, UK scientists claim that the Earth never froze over completely during the Cryogenian Period, about 840 to 635 million years ago.

This is contrary to the Snowball Earth hypothesis, which envisages a fully frozen Earth that was locked in ice for many millions of years as a result of a runaway chain reaction that caused the planet to cool.

What enabled the Earth to escape from a complete freeze is not certain, but the UK scientists in their review point to recent research carried out at the University of Toronto. This speculates that the advancing ice was stalled by the interaction of the physical climate system and the carbon cycle of the ocean, with carbon dioxide playing a key role in insulating the planet.

The Toronto scientists say that as Earth’s temperatures cooled, oxygen was drawn into the ocean, where it oxidized organic matter, releasing the greenhouse gas carbon dioxide into the atmosphere.

The review’s lead author, Professor Phillip Allen, from Imperial College London’s Department of Earth Science and Engineering, says that something must have kept the planet’s equatorial oceans from freezing over. He adds:

“In the climate change game, carbon dioxide can be both saint and sinner. These days we are so concerned about global warming and the harm that carbon dioxide is doing to our planet. However, approximately 600 million years ago, this greenhouse gas probably saved ancient Earth and its basic life forms from an icy extinction.”

Professor Allen, whose previous research has found evidence demonstrating hot and cold cycles in the Cryogenian period, says a plethora of papers has been published and much debate has been devoted to the Snowball Earth theory since it was originally proposed. He says:

“Sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans. This evidence contradicts the Snowball Earth theory, which suggests the oceans were frozen over. Yet, many scientists still believe Snowball Earth to be correct.”

Professor Allen hopes his review in Nature will prompt climate modellers to realign their thinking about the Cryogenian period and review their models to reflect a warmer Earth during this time. He adds:

“There is so much about Earth’s ancient past that we don’t know enough about. So it is really important that climate modellers get their targets right. They need to build into their calculations a warmer planet, with open oceans, despite lower levels of solar radiation at this time. Otherwise, climate models about the Earth’s distant past are aiming for a target that never existed.”

Potential for large earthquake off coast of Sumatra remains large

The subduction zone that brought us the 2004 Sumatra-Andaman earthquake and tsunami is ripe for yet another large event, despite a sequence of quakes that occurred in the Mentawai Islands area in 2007, according to a group of earthquake researchers led by scientists from the Tectonics Observatory at the California Institute of Technology (Caltech).

“From what we saw,” says geologist Jean-Philippe Avouac, director of the Tectonics Observatory and one of the paper’s lead authors, “we can say with some confidence that we’re probably not done with large earthquakes in Sumatra.”

Their findings were published in a letter in the December 4 issue of the journal Nature.

The devastating magnitude 9.2 earthquake that occurred off the western coast of Sumatra on December 26, 2004-the earthquake that spawned a lethal tsunami throughout the Indian Ocean-took place in a subduction zone, an area where one tectonic plate dips under another, forming a quake-prone region.

It is that subduction zone that drew the interest of the Caltech-led team. Seismic activity has continued in the region since the 2004 event, they knew. But have the most recent earthquakes been able to relieve the previous centuries of built-up seismic stress?

Yes . . . and no. Take, for instance, an area just south of the 2004 quake, where a magnitude 8.6 earthquake hit in 2005. (That same area had also been the site of a major earthquake in 1861.) The 2005 quake, says Avouac, did a good job of “unzipping” the stuck area in that patch of the zone, effectively relieving the stresses that had built up since 1861. This means that it should be a few centuries before another large quake in that area would be likely.

The same cannot be said, however, of the area even further south along that same subduction zone, near the Mentawai Islands, a chain of about 70 islands off the western coasts of Sumatra and Indonesia. This area, too, has been hit by giant earthquakes in the past (an 8.8 in 1797 and a 9.0 in 1833). More recently, on September 12, 2007, it experienced two earthquakes just 12 hours apart: first a magnitude 8.4 quake and then a magnitude 7.9.

These earthquakes did not come as a surprise to the Caltech researchers. Caltech geologist and paper coauthor Kerry Sieh, who is now at the Nanyang Technological University in Singapore, had long been using coral growth rings to quantify the pattern of slow uplift and subsidence in the Mentawai Islands area; that pattern, he and his colleagues knew, is the result of stress build-up on the plate interface, which should eventually be released by future large earthquakes.

But was all that accumulated stress released in 2007? In the work described in the Nature letter, the researchers analyzed seismological records, remote sensing (inSAR) data, field measurements, and, most importantly, data gathered by an array of continuously recording GPS stations called SuGAr (for Sumatra Geodetic Array) to find out.

Their answer? The quakes hadn’t even come close to doing their stress-reduction job. “In fact,” says Ali Ozgun Konca, a Caltech scientist and the paper’s first author, who did this work as a graduate student, “we saw release of only a quarter of the moment needed to make up for the accumulated deficit over the past two centuries.” (Moment is a measure of earthquake size that takes into account how much the fault slips and over how much area.)

“The 2007 quakes occurred in the right place at the right time,” adds Avouac. “They were not a surprise. What was a surprise was that those earthquakes were way smaller than we expected.”

“The quake north of this region, in 2005, ruptured completely,” says Konca. “But the 2007 sequence of quakes was more complicated. The slippage of the plates was patchy, and it didn’t release all the strain that had accumulated.”

“It was what we call a partial rupture,” adds Avouac. “There’s still enough strain to create another major earthquake in that region. We may have to wait a long time, but there’s no reason to think it’s over.”

Foretelling a major meltdown

By discovering the meaning of a rare mineral that can be used to track ancient climates, Binghamton University geologist Tim Lowenstein is helping climatologists and others better understand what we’re probably in for over the next century or two as global warming begins to crank up the heat – and, ultimately, to change life as we know it.

“I think the earth will be a very different place in the next hundred years or so, and that many species will adapt to it and many won’t,” Lowenstein said. “Humans are supremely good at adapting. But, rich countries will adapt much better than poor countries and other species will have far more trouble coping with environmental change. There are going to be challenges we can’t even imagine right now.”

Lowenstein’s concerns are rooted not in speculation about unprecedented future happenings, but in the scientific discovery and analysis of mineral samples formed during the Eocene Epoch, the warmest period on earth in the last 65 million years.

What Lowenstein and his colleague Robert Demicco at Binghamton University have discovered is that nahcolite, a rare, yellowish-green or brown carbonate mineral, only forms on earth under environmental conditions marked by very high atmospheric CO2 levels. That establishes it as both a marker and a benchmark that can be used by scientists as they consider the likely climatic implications of ever-increasing CO2 levels in our atmosphere today. More specifically, nahcolite suggests that Eocene warming was concurrent with atmospheric CO2 levels of at least 1,125 parts per million (ppm), which is 3 times the current levels of 380 ppm, but not all that much higher than we can expect on earth in the next 100 years or so given generally accepted scientific projections based on fossil-fuel consumption.

Because CO2 is a forcing factor for climate change, increases in its levels can be directly tied to global warming. A greenhouse gas, CO2 absorbs radiation that would normally be reflected out of the atmosphere, helping to ramp up temperatures, melt glaciers and significantly alter ocean currents and weather patterns.

As for steep, projected increases in CO2 levels over the next century, Lowenstein thinks that might not be our only cause for concern.

“If we assume that you and I are both in our 50s, the change in atmospheric CO2 in our lifetime is greater than the rate of any change in at least the last half million years,” said Lowenstein, who is particularly concerned about unexpected changes

“Right now, we’re on a predictable pace. But there will likely be tipping points, unexpected events that could really change things, so all of a sudden we may get changes in ocean circulation that we never would have predicted, or the tundra may melt. Some unexpected event is going to occur that’s going to be more dramatic than the progressive changes that occurred over the last 100 years.”

As a scientist, Lowenstein has no doubt that burning oil, gas and coal are fueling global warming and creating, along with environmental degradation, an immediate threat to some species of life on the planet. His opinion is unchanged by those who would point to the earth’s ancient hothouse past as proof that natural swings in climate take place with or without human intervention.

Lowenstein said these consequences seem more and more likely without drastic change.

“The glacier on Mount Kilimanjaro has not much time left even now. Many mountain glaciers are going to disappear,” he said. “It all depends on how much fossil fuel we burn. But if we keep doing what we’re doing now, we will be up to the CO2 levels of the Eocene within another 100 or 200 years.”

As Lowenstein points out, although it is difficult to predict how global temperatures over the coming centuries will compare to the Eocene, the “hothouse” world 50 million years ago should serve as a reminder of what global changes are possible.

Team sets records in simulating seismic wave propagation across the Earth

To learn more about the inner sanctum of the earth's core, seismologists take advantage of one of nature's most destructive forces: earthquakes. Somewhat like the way a CAT scan images the brain, seismologists track seismic wave patterns from earthquakes to model the structure of the earth's core. One of the great challenges is to capture the propagation of high-frequency waves, with periods of 1 to 2 seconds, as they travel across the globe. To simulate this activity, seismologists employ a spectral-element application called SPECFEM3D_GLOBE that uses a fine mesh of hexahedral finite elements, pictured here, and high-performance computers. -  D. Komatitsch, Université de Pau; L. Carrington, San Diego Supercomputer Center at UC San Diego.
To learn more about the inner sanctum of the earth’s core, seismologists take advantage of one of nature’s most destructive forces: earthquakes. Somewhat like the way a CAT scan images the brain, seismologists track seismic wave patterns from earthquakes to model the structure of the earth’s core. One of the great challenges is to capture the propagation of high-frequency waves, with periods of 1 to 2 seconds, as they travel across the globe. To simulate this activity, seismologists employ a spectral-element application called SPECFEM3D_GLOBE that uses a fine mesh of hexahedral finite elements, pictured here, and high-performance computers. – D. Komatitsch, Université de Pau; L. Carrington, San Diego Supercomputer Center at UC San Diego.

A team led by researchers at the San Diego Supercomputer Center at UC San Diego has successfully completed record-setting, petascale-level simulations of the earth’s inner structure, paving the way for seismologists to model seismic wave propagations at frequencies of just over one second – the same frequencies that occur in nature.

Results of these latest seismic wave simulations were announced at SC08, the international conference for high-performance computing, where the research by the SDSC-led team was a finalist for Gordon Bell prize, awarded annually for outstanding achievement in high-performance computing applications. The SDSC team includes researchers from the California Institute of Technology; Université de Pau and INRIA, France; and the Institut Universitaire de France, France.

The record runs were completed on the ‘Jaguar’ system at Oak Ridge National Laboratory (ORNL). The record run broke the two-second barrier by achieving a shortest period of 1.15 seconds and 161 teraflops, using 149,784 cores.

That is the shortest wave period ever obtained in seismic wave propagation, as well as the highest level of parallelism and the first sustained performance of seismic wave propagation exceeding 160 TFlops. (One teraflop equals one trillion calculations per second. To put that in perspective, it would take a person operating a hand-held calculator more than 30,000 years to complete one trillion calculations.)

The latest supercomputer simulations, led by SDSC researcher Laura Carrington, focused on overcoming a key challenge in global seismology: modeling the propagation of seismic waves with frequencies as small as one second. The team broke the previous record set in 2003, which achieved frequencies of 3.5 seconds.

“In breaking the two-second barrier, we were able to model wave propagation clear through the Earth to more accurately predict its structure,” said Carrington, who is with SDSC’s Performance Modeling and Characterization (PMaC) laboratory. “More significantly, by achieving a frequency just above one second, we were able to duplicate the same frequencies that occur in nature, providing an unprecedented level of resolution that will greatly enhance our understanding of the physics and chemistry of the Earth’s interior.”

Researchers used a spectral finite-element application called SPECFEM3D_GLOBE for the latest and largest simulations ever done in this area of research. Waves at frequencies of between one and two seconds, generated when major earthquakes with magnitudes measuring 6.5 or more occur, help reveal new information about the 3D structure of the Earth because they are the highest frequency signals that can propagate, or travel, all the way through the Earth, particularly near the core-mantle boundary (CMB), the inner core boundary (ICB), and the enigmatic inner core, which is comprised of solid iron.

There is no need to simulate wave periods of less than one second for seismographic comparisons, because such frequencies signals do not propagate across the entire globe, according to the researchers.

Moreover, the team’s research is crucial in helping seismologists better understand the dramatic differences in the complex structure of the Earth’s inner core, which appears to be anisotropic, or having unequal physical properties along different axes, with dramatic differences between its eastern and western hemispheres.

Earlier, the research team conducted simulations using a wide range of resources provided by the TeraGrid, the nation’s largest open scientific discovery infrastructure linking compute resources among 11 partner sites across the U.S. Runs were conducted using approximately 32,000 cores on the ‘Ranger’ supercomputer at the Texas Advanced Computing Center (TACC) at The University of Texas in Austin. That run achieved a seismic period length of 1.84 seconds and at a sustained 28.7 TFlops.

Prior to that, the team successfully completed several simulations using TeraGrid supercomputer resources, including 29,000 cores on the ‘Jaguar’ system at ORNL’s National Center for Computational Sciences, achieving 1.94 seconds at 35.7 TFlops. Runs were also conducted on the Cray XT4 ‘Franklin’ system at the National Energy Research Scientific Computing Center (NERSC) at the Lawrence Berkeley National Laboratory in Berkeley, Calif.; (12,150 cores with a shortest seismic wave of 3 seconds at 24 TFlops), and on the Cray XT4 ‘Kraken’ system at the University of Tennessee-Knoxville (17,496 cores at 2.52 seconds at 22.4T Flops. The TFlops number in these and subsequent runs were measures using PSiNSlight, a performance measurement and tracing tool developed by SDSC’s PMaC Lab.

The researchers also made a number of radical structure and memory management changes to the SPECFEM3D_GLOBAL application to enable what researchers call “peta-scale-ability”, or using processors numbering in the hundreds of thousands. Efforts focused on the application to overlapping communications using non blocking MPI calls, optimizations to reduce cache misses, optimization to reduce I/O, large restructurings to reducing memory consumption, and work to reduce memory fragmentation.

In addition to Carrington, SDSC researchers on the team include Allan Snavely, director of the PMaC Lab; and researchers Michael Laurenzano and Mustafa Tikir. Additional team members include Dimitri Komatitsch, David Michéa, and Nicolas Le Goff of the Université de Pau, CNRS and INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences, Pau, France; and Jeroen Tromp, formerly a professor of geophysics with the California Institute of Technology’s Seismological Laboratory. Tromp recently joined Princeton University’s geosciences and mathematics departments. Komatitsch is also affiliated with the Institut Universitaire de France, in Paris.

Komatitsch and Tromp developed SPECFEM3D_GLOBE over 10 years ago, in order to do 3D whole Earth models that account for geological variations in and under the Earth’s crust. These variations have a dramatic effect on how earthquakes propagate. Komatitsch’s work on the application was vital in the collaboration that accomplished this record breaking run.

About the run, Tromp and Komatitsch had this to say: “One of the long-term goals of seismology is to be able to routinely simulate 3D seismic wave propagation in the whole Earth following earthquakes at frequencies of about 1 Hz, the highest frequency signal that can be seen clear across the planet. Very large numerical simulations performed on the new Cray XT5 system at Oak Ridge will enable us to get increasingly closer to this lofty goal.”

Meteorite hits on Earth: There may be a recount

Meteorite craters might not be as rare as we think. A University of Alberta researcher has found a tool that could reveal possibly hundreds of undiscovered craters across Canada and around the world.

The discovery of a meteorite crater near Whitecourt, 200 kilometers west of Edmonton, Alberta, Canada prompted Chris Herd to examine the site from the air using existing aerial surveys. A computer program, applied to aerial images taken by a forestry company, stripped away the images of trees to expose the landscape, revealing the meteorite crater.

Herd, an assistant professor in the U of A’s department of earth and atmospheric sciences, says this technology can be used to potentially reveal hundreds of meteorite craters around the world that are hidden by trees but unknowingly captured on aerial forest surveys.

Herd believes that as more craters are found and analyzed existing theories on how many meteorites have hit Earth in the past and the frequency of future impacts will change.

Herd’s research will be published in the journal, Geology, on Nov. 25.