Ground-breaking study warns of more great quakes in the Himalayas

A research team led by scientists from Nanyang Technological University (NTU) has discovered that massive earthquakes in the range of 8 to 8.5 magnitudes on the Richter scale have left clear ground scars in the central Himalayas.

This ground-breaking discovery has huge implications for the area along the front of the Himalayan Mountains, given that the region has a population density similar to that of New York City.

NTU Professor Paul Tapponnier, who is recognised as a leading scientist in the field of neotectonics, said that the existence of such devastating quakes in the past means that quakes of the same magnitude could happen again in the region in future, especially in areas which have yet to have their surface broken by a temblor.

Published recently in Nature Geosciences, a prestigious scientific journal, the study by NTU’s Earth Observatory of Singapore (EOS) and colleagues in Nepal and France showed that in 1255 and 1934, two great earthquakes ruptured the surface of the earth in the Himalayas. This runs contrary to what scientists have previously thought.

Massive earthquakes are not unknown in the Himalayas, as quakes in 1897, 1905, 1934 and 1950 all had magnitudes between 7.8 and 8.9, each causing tremendous damage. But they were previously thought not to have broken the earth’s surface – classified as blind quakes – which are much more difficult to track.

However, Prof Tapponnier said that by combining new high resolution imagery and state of the art dating techniques, they could show that the 1934 earthquake did indeed rupture the surface, breaking the ground over a length of more than 150 kilometres, essentially south of the part of the range that harbours Mt Everest.

This break formed along the main fault in Nepal that currently marks the boundary between the Indian and Asian tectonic plates – also known as the Main Frontal Thrust (MFT) fault.

Using radiocarbon dating of offset river sediments and collapsed hill-slope deposits, the research team managed to separate several episodes of tectonic movement on this major fault and pin the dates of the two quakes, about 7 centuries apart.

“The significance of this finding is that earthquakes of magnitude 8 to 8.5 may return at most twice per millennium on this stretch of the fault, which allows for a better assessment of the risk they pose to the surrounding communities,” said Prof Tapponnier.

Prof Tapponnier warns that the long interval between the two recently discovered earthquake ruptures does not mean people should be complacent, thinking that there is still time before the next major earthquake happens in the region.

“This does not imply that the next mega-earthquake in the Himalayas will occur many centuries from now because we still do not know enough about adjacent segments of the MFT Mega-thrust,” Prof Tapponier explains.

“But it does suggest that areas west or east of the 1934 Nepal ground rupture are now at greater risk of a major earthquake, since there are little or no records of when last earth shattering temblor happened in those two areas.”

The next step for Prof Tapponnier and his EOS scientists is to uncover the full extent of such fault ruptures, which will then allow them to build a more comprehensive model of earthquake hazard along the Himalayan front.

About the NTU’s Earth Observatory of Singapore (EOS)

EOS is a premier research institute at NTU which conducts fundamental research on earthquakes, volcanic eruptions, tsunami and climate change in and around Southeast Asia, towards safer and more sustainable societies.

Meteorite triggered scientific gold rush

Qing-Zhu Yin, professor of geology at UC Davis, shows a 5.4-gram meteorite fragment, which was part of the Sutter's Mill meteorite that fell over Northern California on April 22, 2012. Gregory Jorgensen, a UC Davis alum, found the meteorite on his driveway and donated it to UC Davis. -  Gregory Urquiaga/UC Davis
Qing-Zhu Yin, professor of geology at UC Davis, shows a 5.4-gram meteorite fragment, which was part of the Sutter’s Mill meteorite that fell over Northern California on April 22, 2012. Gregory Jorgensen, a UC Davis alum, found the meteorite on his driveway and donated it to UC Davis. – Gregory Urquiaga/UC Davis

A meteorite that exploded as a fireball over California’s Sierra foothills this past spring was among the fastest, rarest meteorites known to have hit the Earth, and it traveled a highly eccentric orbital route to get here.

An international team of scientists presents these and other findings in a study published Friday, Dec. 21, in the journal Science. The 70-member team included nine researchers from UC Davis, along with scientists from the SETI Institute, NASA and other institutions.

The researchers found that the meteorite that fell over Northern California on April 22 was the rarest type known to have hit the Earth – a carbonaceous chondrite. It is composed of cosmic dust and presolar materials that helped form the planets of the solar system.

The scientists learned that the meteorite formed about 4.5 billion years ago. It was knocked off its parent body, which may have been an asteroid or a Jupiter-family comet, roughly 50,000 years ago. That began its journey to Sutter’s Mill, the gold discovery site that sparked the California Gold Rush.

As it flew toward Earth, it traveled an eccentric course through the solar system, flying from an orbit close to Jupiter toward the sun, passing by Mercury and Venus, and then flying out to hit Earth.

The high-speed, minivan-sized meteorite entered the atmosphere at about 64,000 miles per hour. The study said it was the fastest, “most energetic” reported meteorite that’s fallen since 2008, when an asteroid fell over Sudan.

“If this were a much bigger object, it could have been a disaster,” said co-author and UC Davis geology professor Qing-zhu Yin. “This is a happy story in this case. “

Before entering Earth’s atmosphere, the meteorite is estimated to have weighed roughly 100,000 pounds. Most of that mass burned away when the meteorite exploded. Scientists and private collectors have recovered about 2 pounds remaining.

UC Davis is 60 miles west of the El Dorado county towns of Coloma and Lotus, where pieces of the meteorite were found on residents’ driveways and in local forests and parks.

When the meteorite fell, Yin, whose lab contains some of the country’s most specialized equipment to measure the age and composition of meteorites, searched for and collected pieces of the fallen meteorite with students and volunteers. He also lead a 35-member subgroup of international researchers to study and share information about the meteorite’s mineralogy, internal textures, chemical and isotopic compositions and magnetic properties.

Meteorites like Sutter’s Mill are thought to have delivered oceans of water to the Earth early in its history. Using neutron-computed tomography, UC Davis researchers helped identify where hydrogen, and therefore water-rich fragments, resides in the meteorite without breaking it open.

For the first time, the Doppler weather radar network helped track the falling carbonaceous chondrite meteorite pieces, aiding scientists in the quick recovery of them, the study reports. Yin expects that the weather radar data in the public domain could greatly enhance and benefit future meteorite recoveries on land.

“For me, the fun of this scientific gold rush is really just beginning,” said Yin. “This first report based on the initial findings provides a platform to propel us into more detailed research. Scientists are still finding new and exciting things in Murchison, a similar type of meteorite to Sutter’s Mill, which fell in Victoria, Australia, in 1969, the same year Apollo astronauts Neil Armstrong and Buzz Aldrin returned the first lunar samples to the Earth. We will learn a lot more with Sutter’s Mill.”

When the ice melts, the Earth spews fire

In 1991, it was a disaster for the villages nearby the erupting Philippine volcano Pinatubo. But the effects were felt even as far away as Europe. The volcano threw up many tons of ash and other particles into the atmosphere causing less sunlight than usual to reach the Earth’s surface. For the first few years after the eruption, global temperatures dropped by half a degree. In general, volcanic eruptions can have a strong short-term impact on climate. Conversely, the idea that climate may also affect volcanic eruptions on a global scale and over long periods of time is completely new. Researchers at GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany) and Harvard University in Massachusetts (USA) have now found strong evidence for this relationship from major volcanic eruptions around the Pacific Ocean over the past 1 million years. They have presented their results in the latest issue of the international journal “Geology“.

The basic evidence for the discovery came from the work of the Collaborative Research Centre “Fluids and Volatiles in Subduction Zones (SFB 574). For more than ten years the project has been extensively exploring volcanoes of Central America. “Among others pieces of evidence, we have observations of ash layers in the seabed and have reconstructed the history of volcanic eruptions for the past 460,000 years,” says GEOMAR volcanologist Dr Steffen Kutterolf, who has been with SFB 574 since its founding. Particular patterns started to appear. “There were periods when we found significantly more large eruptions than in others” says Kutterolf, the lead author of the Geology article.

After comparing these patterns with the climate history, there was an amazing match. The periods of high volcanic activity followed fast, global temperature increases and associated rapid ice melting. To expand the scope of the discoveries, Dr Kutterolf and his colleagues studied other cores from the entire Pacific region. These cores had been collected as part of the International Integrated Ocean Drilling Program (IODP) and its predecessor programmes. They record more than a million years of the Earth’s history. “In fact, we found the same pattern from these cores as in Central America” says geophysicist Dr Marion Jegen from GEOMAR, who also participated in the recent study.

Together with colleagues at Harvard University, the geologists and geophysicists searched for a possible explanation. They found it with the help of geological computer models. “In times of global warming, the glaciers are melting on the continents relatively quickly. At the same time the sea level rises. The weight on the continents decreases, while the weight on the oceanic tectonic plates increases. Thus, the stress changes within in the earth to open more routes for ascending magma” says Dr Jegen.

The rate of global cooling at the end of the warm phases is much slower, so there are less dramatic stress changes during these times. “If you follow the natural climate cycles, we are currently at the end of a really warm phase. Therefore, things are volcanically quieter now. The impact from man-made warming is still unclear based on our current understanding” says Dr Kutterolf. The next step is to investigate shorter-term historical variations to better understand implications for the present day.

Analysis of Marcellus flowback finds high levels of ancient brines

Brine water that flows back from gas wells in the Marcellus Shale region after hydraulic fracturing is many times more salty than seawater, with high contents of various elements, including radium and barium. The chemistry is consistent with brines formed during the Paleozoic era, a study by an undergraduate student and two professors in Penn State’s Department of Geosciences found.

The study indicates that the brine flowback elements found in high levels in the late stages of hydraulic fracturing come from the ancient brines rather than from salts dissolved by the water and chemicals used as part of the fracking process. The paper by Lara O. Haluszczak, a Penn State student who has since graduated; professor emeritus Arthur W. Rose; and Lee R. Kump, professor and head of the Department of Geosciences, detailing those findings has been accepted for publication in Applied Geochemistry, the journal of the International Association of Geochemistry, and is available online.

For the study, the researchers analyzed data primarily from four sources: a report on brines from 40 conventional oil and gas wells in Pennsylvania; data on flowback waters from 22 Marcellus gas wells in Pennsylvania that the state Bureau of Oil and Gas Management had collected; flowback waters from two Marcellus gas wells from a previous study; and an industry study by the Marcellus Shale Coalition on flowback samples from eight horizontal wells that was reported in a Gas Technology Institute report.

Hydraulic fracturing, or fracking, is the process used to release natural gas from the shale formations deep underground. The process involves drilling down thousands of feet and, in the case of horizontal wells, sideways, then injecting a mixture of water, sand and chemicals to release the gas. The paper notes that about a quarter of the volume of fluid used for fracking returns to the surface, but with the brine as a major component.

The paper looked at fluids that flowed back within 90 days of fracking. The samples analyzed in the study come from wells in Pennsylvania, along with two from northern Virginia.

The analysis shows that the brine flowback had extremely high salinity that does not match the chemical composition of the solution put into the wells during the fracking process. Instead, the elements being released are similar to those deposited during the Paleozoic era, hundreds of millions of years ago.

Rose said the naturally occurring radioactive materials being brought to the surface after having been 8,000 feet deep were deposited with formations in that era. He noted that while much attention has been focused on the chemicals that are injected into the shale formation during the fracking process, also of concern is the release of elements such as barium and radium that have been in the ground for millions of years.

“Even if it’s diluted quite a bit, it’s still going to be above the drinking water limits,” Rose said. “There’s been very little research into this.”
Pennsylvania does have regulations on the disposal of fracking fluids. Rose said the findings highlight the importance of re-use and proper disposal of fracking fluids, including those from the later stages of drilling.

“Improper disposal of the flowback can lead to unsafe levels of these and other constituents in water, biota and sediment from wells and streams,” the researchers noted.

“The high salinity and toxicity of these waters must be a key criterion in the technology for disposal of both the flowback waters and the continuing outflow of the production waters,” the paper concludes.

Antarctic meteorite hunters

For more than 35 years, scientists from the Antarctic Search for Meteorites (ANSMET) program have been scouring glacial landscapes in search of meteorites. Since 1976, teams of physicists, meteorite specialists, and mountaineers have recovered thousands of untouched specimens from meteoroids, the moon and even Mars. Despite subzero temperatures and razor-sharp winds, scientists are lining up for the chance to experience the ultimate hunt for alien objects in the alien environment.

ANSMET teams either conduct systematic searches of a region or work as a scout teams making preliminary investigations of new sites that might be worth further exploration. Once discovered, the meteorites are carefully cataloged in the field and sent to the Smithsonian’s National Museum of Natural History in Washington, D.C., where they are distributed to scientists for further research. What secrets will new specimens – locked away in the ice and yet to be discovered – hold about our solar system and the universe? Read the story online and find out at http://bit.ly/UtXc9R.

Read this story and more in the December issue of EARTH Magazine, available online now. Learn how mummification emerged from environmental change; discover the explosive combination of red giants and white dwarfs; and see what states are paying to dispose of low-level radioactive waste all in this month’s issue of EARTH.

Tsunami caused long-term ecosystem change in the Caribbean

A detailed analysis of sediments from the island of Bonaire in the Caribbean presents convincing evidence for an extraordinary wave impact dating back some 3,300 years, even though no historical records of tsunamis exist for this island. Of particular interest are the consequences this large wave impact had on the island’s ecosystem. The sediments studied by the scientists suggested that this tsunami entirely changed the coastal ecosystem and sedimentation patterns in the area. The work by Dr. Max Engel and colleagues, from the University of Köln in Germany, is published online in Springer’s journal, Naturwissenschaften – The Science of Nature.

The Caribbean region is highly vulnerable to coastal hazards, including tropical cyclones, earthquakes, volcanoes, and tsunamis. Even though the island of Bonaire has not experienced a tsunami during the past 500 years, which is the period of historical documentation, overwash deposits from a coastal lagoon provide evidence for at least one such event in prehistory.

Engel and colleagues investigated sediment cores from Washington-Slagbaai National Park. They looked specifically at grain size distribution, carbonate content, organic matter, magnetic susceptibility and fauna. Their analyses showed that the sediments had criteria typically linked with tsunami deposits, consistent with a tsunami with a maximum age of 3,300 years.

The authors conclude: “This single catastrophic event is of long-term ecological significance. Formation of a barrier of coral rubble was triggered by the tsunami separating a former inland bay from the open sea and turning it into a highly saline lagoon which persists until today. Further studies of the geology of tsunamis, using well-dated deposits, are required over the entire Caribbean to reconstruct reliable patterns of magnitude, frequency and spatial occurrence of tsunami events and their environmental impact.”

The bright future for natural gas in the United States

Hydraulic fracturing, or “fracking,” has changed the energy landscape. We can now affordably produce natural gas from previously inaccessible rock formations, which has led to increasing natural gas consumption. Thanks to its low prices and abundant domestic supply, natural gas may have a chance to overtake coal as the primary energy source for electricity in the United States.

Natural gas has been a part of our energy economy for more than a century; however, it wasn’t until recently that it started to play a key role. While it has always been useful for cooking and heating, over the past few decades natural gas has started to become a main source for power generation and transportation. Although the price of natural gas today is quite low in comparison to other fuel sources, it hasn’t always been low and there’s no guarantee it will stay low. How will natural gas affect our domestic energy mix in the future? Read the story online and find out: http://bit.ly/123dRGS.

Mining ancient ores for clues to early life

One of the sulfide ore samples analyzed for the study. The bright area in the lower left, a 'sulfide nodule,' preserves isotopic evidence of the presence of microbes that fed on sulfate in the ancient ocean. -  Mark. D. Hannington
One of the sulfide ore samples analyzed for the study. The bright area in the lower left, a ‘sulfide nodule,’ preserves isotopic evidence of the presence of microbes that fed on sulfate in the ancient ocean. – Mark. D. Hannington

An analysis of sulfide ore deposits from one of the world’s richest base-metal mines confirms that oxygen levels were extremely low on Earth 2.7 billion years ago, but also shows that microbes were actively feeding on sulfate in the ocean and influencing seawater chemistry during that geological time period.

The research, reported by a team of Canadian and U.S. scientists in Nature Geoscience, provides new insight into how ancient metal-ore deposits can be used to better understand the chemistry of the ancient oceans – and the early evolution of life.

Sulfate is the second most abundant dissolved ion in the oceans today. It comes from the “rusting” of rocks by atmospheric oxygen, which creates sulfate through chemical reactions with pyrite, the iron sulfide material known as “fool’s gold.”

The researchers, led by PhD student John Jamieson of the University of Ottawa and Prof. Boswell Wing of McGill, measured the “weight” of sulfur in samples of massive sulfide ore from the Kidd Creek copper-zinc mine in Timmins, Ontario, using a highly sensitive instrument known as a mass spectrometer. The weight is determined by the different amounts of isotopes of sulfur in a sample, and the abundance of different isotopes indicates how much seawater sulfate was incorporated into the massive sulfide ore that formed at the bottom of ancient oceans. That ancient ore is now found on the Earth’s surface, and is particularly common in the Canadian shield.

The scientists found that much less sulfate was incorporated into the 2.7 billion-year-old ore at Kidd Creek than is incorporated into similar ore forming at the bottom of oceans today. From these measurements, the researchers were able to model how much sulfate must have been present in the ancient seawater. Their conclusion: sulfate levels were about 350 times lower than in today’s ocean. Though they were extremely low, sulfate levels in the ancient ocean still supported an active global population of microbes that use sulfate to gain energy from organic carbon.

“The sulfide ore deposits that we looked at are widespread on Earth, with Canada and Quebec holding the majority of them,” says Wing, an associate professor in McGill’s Department of Earth and Planetary Science. “We now have a tool for probing when and where these microbes actually came into global prominence.”

“Deep within a copper-zinc mine in northern Ontario that was once a volcanically active ancient seafloor may not be the most intuitive place one would think to look for clues into the conditions in which the earliest microbes thrived over 2.7 billion years ago,” Jamieson adds. “However, our increasing understanding of these ancient environments and our abilities to analyze samples to a very high precision has opened the door to further our understanding of the conditions under which life evolved.”

Asteroid that killed the dinosaurs also wiped out the ‘Obamadon’

The asteroid collision widely thought to have killed the dinosaurs also led to extreme devastation among snake and lizard species, according to new research – including the extinction of a newly identified lizard species Yale and Harvard scientists have named Obamadon gracilis.

“The asteroid event is typically thought of as affecting the dinosaurs primarily,” said Nicholas R. Longrich, a postdoctoral associate with Yale’s Department of Geology and Geophysics and lead author of the study. “But it basically cut this broad swath across the entire ecosystem, taking out everything. Snakes and lizards were hit extremely hard.”

The study was scheduled for online publication the week of Dec. 10 in the Proceedings of the National Academy of Sciences.

Earlier studies have suggested that some snake and lizard species (as well as many mammals, birds, insects and plants) became extinct after the asteroid struck the earth 65.5 million years ago, on the edge of the Yucatan Peninsula. But the new research argues that the collision’s consequences were far more serious for snakes and lizards than previously understood. As many as 83 percent of all snake and lizard species died off, the researchers said – and the bigger the creature, the more likely it was to become extinct, with no species larger than one pound surviving.

The results are based on a detailed examination of previously collected snake and lizard fossils covering a territory in western North America stretching from New Mexico in the southwestern United States to Alberta, Canada. The authors examined 21 previously known species and also identified nine new lizards and snakes.

They found that a remarkable range of reptile species lived in the last days of the dinosaurs. Some were tiny lizards. One snake was the size of a boa constrictor, large enough to take the eggs and young of many dinosaur species. Iguana-like plant-eating lizards inhabited the southwest, while carnivorous lizards hunted through the swamps and flood plains of what is now Montana, some of them up to six feet long.

“Lizards and snakes rivaled the dinosaurs in terms of diversity, making it just as much an ‘Age of Lizards’ as an ‘Age of Dinosaurs,'” Longrich said.

The scientists then conducted a detailed analysis of the relationships of these reptiles, showing that many represented archaic lizard and snake families that disappeared at the end of the Cretaceous, following the asteroid strike.

One of the most diverse lizard branches wiped out was the Polyglyphanodontia. This broad category of lizards included up to 40 percent of all lizards then living in North America, according to the researchers. In reassessing previously collected fossils, they came across an unnamed species and called it Obamadon gracilis. In Latin, odon means “tooth” and gracilis means “slender.”

“It is a small polyglyphanodontian distinguished by tall, slender teeth with large central cusps separated from small accessory cusps by lingual grooves,” the researchers write of Obamadon, which is known primarily from the jaw bones of two specimens. Longrich said the creature likely measured less than one foot long and probably ate insects.

He said no one should impute any political significance to the decision to name the extinct lizard after the recently re-elected U.S. president: “We’re just having fun with taxonomy.”

The mass (but not total) extinction of snakes and lizards paved the way for the evolution and diversification of the survivors by eliminating competitors, the researchers said. There are about 9,000 species of lizard and snake alive today. “They didn’t win because they were better adapted, they basically won by default, because all their competitors were eliminated,” Longrich said.

Co-author Bhart-Anjan S. Bhullar, a doctoral student in organismic and evolutionary biology at Harvard University, said:

“One of the most important innovations in this work is that we were able to precisely reconstruct the relationships of extinct reptiles from very fragmentary jaw material. This had tacitly been thought impossible for creatures other than mammals. Our study then becomes the pilot for a wave of inquiry using neglected fossils and underscores the importance of museums like the Yale Peabody as archives of primary data on evolution – data that yield richer insights with each new era of scientific investigation.”

Jacques A. Gauthier, professor of geology and geophysics at Yale and curator of vertebrate paleontology and vertebrate zoology, is also an author.

Detecting tunnels using seismic waves not as simple as it sounds

Researchers deploy instruments for a seismic data acquisition survey parallel to a border fence in California. The photo shows some acquisition equipment, including an SUV-mounted accelerated weight drop to generate seismic waves. -  Sandia National Laboratories
Researchers deploy instruments for a seismic data acquisition survey parallel to a border fence in California. The photo shows some acquisition equipment, including an SUV-mounted accelerated weight drop to generate seismic waves. – Sandia National Laboratories

You’d think it would be easy to use seismic waves to find tunnels dug by smugglers of drugs, weapons or people.

You’d be wrong.

Nedra Bonal of Sandia’s geophysics and atmospheric sciences organization is nearing the end of a two-year study, “Improving Shallow Tunnel Detection From Surface Seismic Methods,” aimed at getting a better look at the ground around tunnels and learning why seismic data finds some tunnels but not others.

Her eventual goal is to come up with a seismic detection process for the border and other areas where tunnels pose a security threat. Bonal’s project is funded by Sandia’s Early Career Laboratory Directed Research and Development program.

Most tunnels are found by tips from people rather than by scientific methods, Bonal said.

“It would be great if we could use this to do a better job with tunnel detection, so you could scan an area and know if there is or is not a tunnel and find it and stop it,” she said.

If researchers discover what it takes to pinpoint tunnels, the next step would be to develop streamlined seismic methods that would be more practical for the Border Patrol and military.

The study arose from earlier work at Sandia detecting shallow tunnels. Bonal said she was surprised when standard refraction and reflection processing techniques Sandia used could not successfully pinpoint some tunnels.

Researchers speculate the difficulty might be what’s called a halo effect around a tunnel, in which fracturing and other geological anomalies create diffuse boundaries and hide the tunnel. The earlier, broader research produced several successes in tunnel detection, but was not focused specifically on what happens in the area where tunnel and earth meet, which might help explain why tunnels can be detected in some cases but not others.

Bonal is looking at whether seismic waves are strongly impacted by fracturing or saturation of pores in rock or soil, as well as varying pressures at different depths. Physical processes change from shallow depths to deeper depths, but it isn’t clear just where that change occurs, she said.

In addition, the halo effect is both asymmetrical and complex.

“It depends on the geology or the soil as well as the seasonal variation, rain events and the relation to the water table,” Bonal said. “So it’s a pretty complex regime just from the hydrology standpoint.”

More research is needed, but asymmetry may turn out to be an advantage because an asymmetric area might show up better than a symmetrical one, she said. “These anomalous areas are what we may identify as tunnels in the data,” she said.

Bonal began her project by figuring out what gaps existed in current scientific knowledge, then modeling real-world scenarios based on collected data that would affect hydrology models and in turn, seismic waves: an area’s soil and other geology, the depth of rock fracturing around a tunnel in a particular environment, the probable tunnel size, its relation to the water table and seasonal variations in that relationship.

“We try to get some bounds to this problem,” she said. “If we can’t see it in the best-case scenario, then there’s really no point in trying to see it in more subtle factors that may affect the seismic waves.”

The team ran the hydrology models to get some results, then converted those results into seismic velocities that could be plugged into Sandia’s 3-D elastic seismic wave propagation simulation code, Bonal said. These results will produce synthetic seismograms that will be compared to field data from the real environment and can be used to develop other processing techniques. That will in turn produce data that’s expected to look like what’s collected in the field.

“We can then compare the effects of a tunnel versus no tunnel and changes in fracturing and saturation of the tunnel halo versus no changes to assess their impact on seismic waves,” she said.

The standard used to show the relationship of saturation in pores in rock or earth to seismic velocities is an oil industry standard called the Biot-Gassmann theory. However, few experiments have tested that theory at shallow depths where border tunnels are commonly dug, Bonal said.

“The few that have been done have shown that the Biot-Gassmann theory tends to overestimate the velocities for those unconsolidated near-surface materials where the pressures perhaps aren’t as great” as at depths where the oil industry operates, she said.

The very near surface behaves one way, but at some point behaviors change because of greater pressures and other factors, she said. The Biot-Gassmann theory holds well at greater depths where pressure is more intense and the rock is more consolidated, while another theory, Brutsaert, describes what happens very close to the surface.

“But there’s sort of a middle regime where I’m looking where I’m not real sure either one of them works as well as they need to,” Bonal said. She expects to have the modeled data results soon to compare with seismic data collected from previous experiments to help resolve the issue.

Experimentally verifying at what depth or in what materials competing theories work best lies outside the scope of her LDRD, but Bonal hopes to work on those puzzles in a future project. “I think there are still plenty of questions we have that need to be answered but I am very excited about the progress made so far. I have been able to detect a tunnel that I previously had not seen by other analyses,” she said.