Tag Archives: geophysics

InSight maps Mars’ composition and chunky core for the first time

We are closer than ever before to understanding the composition of Mars thanks to the first observations of seismic activity on the planet made by the InSight lander. The NASA-led project, which landed on the surface of the Red Planet in November 2018 with the goal of probing beneath the Martian surface, observed several so-called ‘marsquakes’ which reveal details about its crust, mantle, and core.

Using seismic activity or ‘marsquakes’ researchers have detailed the composition of the Martian interior for the first time (Cottaar/ Science)

InSight’s primary findings which are detailed in three papers published today in the journal Science, represent the first time scientists have been able to produce a detailed picture of the interior of a planet other than Earth.

“We are seeking to understand the processes that govern planetary evolution and formation, to discover the factors that have led to Earth’s unique evolution,” says Amir Khan, ETH Zurich and the University of Zurich, whose team used direct and surface reflected seismic waves to reveal the structure of Mars’ mantle. “In this respect, the InSight mission fills a gap in the scientific exploration of the solar system by performing an in-situ investigation of a planet other than our own.”

The results from the ongoing NASA mission–with the full title ‘Interior Exploration using Seismic Investigations, Geodesy and Heat Transport’— could reveal key insights into the Red Planet‘s formation and evolution, as well as helping us understand the key differences between our planet and Mars.

“One big question we would like to understand is why Earth is the only planet with liquid oceans, plate tectonics, and abundant life?” adds Khan. “Mars is presently on the edge of the solar system’s habitable zone and may have been more hospitable in its early history. Whilst we don’t yet know the answers to these questions, we know they to be found are on Mars, most likely within its interior.”

The InSight Lander on the surface of Mars ((NASA/JPL-Caltech))

InSight first detected the presence of marsquakes from its position in Elysium Planitia near the Red Planet’s equator in 2019 and has since picked up more than 300 events–more than 2 a day–tracing many of them back to their source.

What is really impressive is what researchers can do with these quakes, using them as a diagnostic tool to ‘see’ deep into the planet’s interior.

“Studying the signals of marsquakes, we measured the thickness of the crust and the structure of the mantle, as well as the size of the Martian core,” Simon Stähler, a research seismologist at ETH Zurich, tells ZME Science. “This replicates what was done on Earth between 1900 and 1940 using the signals of earthquakes.”

From the Crust of Mars…

The observations made by InSight have allowed researchers to assess the structure of Mars’ crust, allowing them to determine its thickness and other properties in absolute numbers for the first time. The only values we previously had for the Martian crust were relative values that showed differences in thickness from area to area.

“As part of the bigger picture on the interior structure of Mars, we have determined the thickness and structure of the Martian crust,” Brigitte Knapmeyer-Endrun, a geophysicist at the University of Cologne’s Institute of Geology, tells ZME Science. “Previous estimates could only rely on orbital data–gravity and topography–that can accurately describe relative variations in crustal thickness, but no absolute values. These estimates also showed a wide variability.”

The Mars InSight lander’s seismometer consists of a protective dome that contains three extremely sensitive sensors. (NASA/JPL-Caltech)

With data collected regarding the crustal thickness at InSight’s landing area, new seismic measurements, and data collected by previous missions, the team could map the thickness across the entire Martian crust finding an average thickness of between 24 and 72 km.

Knapmeyer-Endrun explains that the data she and her team collected with InSight’s Seismic Experiment for Interior Structure (SEIS), particularly the very broad-band (VBB) seismometer–an instrument so sensitive it can record motion on an atomic scale–and information from the Marsquake Service (MQS) at ETH Zurich, suggest that the Red Planet’s crust is thinner than models have thus far predicted.

“We end up with two possible crustal thicknesses at the landing site–between 39 and 20 km– but both mean that the crust is thinner than some previous estimates and also less dense than what was postulated based on orbital measurements of the surface.”

Knapmeyer-Endrun continues by explaining that the InSight data also reveals the structure of the Martian crust as multi-layered with at least two interfaces that mark a change in composition. In addition to this, the team can’t rule out the presence of a third crustal layer before the mantle.

“The crust shows distinct layering, with a surficial layer of about 10 km thickness that has rather low velocities, implying that it probably consists of rather porous–fractured–rocks, which is not unexpected due to the repeated meteorite impacts,” says the geophysicist adding that we see something similar on the Moon, but the effect is more extreme due to that smaller body’s much thinner atmosphere.

The two largest quakes detected by NASA’s InSight appear to have originated in a region of Mars called Cerberus Fossae. Scientists previously spotted signs of tectonic activity here, including landslides. This image was taken by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter (NASA/JPL-Caltech/University of Arizona)

Knapmeyer-Endrun is pleasantly surprised regarding just how much information InSight has been able to gather with just one seismometer.”It’s surprising we were really able to pull all of this information about the interior of Mars from the recordings of quakes with magnitudes of less than 4.0 from a single seismometer,” she explains. “On Earth, we would not be able to even detect those quakes at a comparable distance. We typically use 10s or even 100s of seismometers for similar studies.”

And the marsquake data collected by InSight has not just proven instrumental in assessing the thickness and composition of the planet’s crust, it has also allowed scientists to probe deeper, to the very core of Mars itself.

…To the Martian Mantle and Core

Using direct and surface reflected seismic waves from eight low-frequency marsquakes Khan and his team probed deeper beneath the surface of Mars to investigate the planet’s mantle. They found the possible presence of a thick lithosphere 500km beneath the Martian surface with an underlying low-velocity layer, similar to that found within Earth. Khan and his co-author’s study reveals that the crustal layer of Mars is likely to be enriched with radioactive elements. These elements heat this region with this warming reducing heat in lower layers.

It was these lower regions that Stähler and his colleagues investigated with the use of faint seismic signals reflected by the boundary between the Martian mantle and the planet’s core. What the team discovered is that the Red Planet’s core is actually larger than previously calculated, with a radius of around 1840 km rather than previous estimates of 1600km. This means the core begins roughly halfway between the planet’s surface and its centre.

From the new information, we can also determine the core’s density and extrapolate its composition.

A Comparison of Mars’ Earth’s interiors. The Martian core shown here is smaller than these new findings suggest. Whilst the crust shown is thicker.



“We now know for sure the size of the core and it’s significantly larger than it had been thought to be for a long time,” says Stähler. “Because we found that the core is quite large, we, therefore, know it is not very dense. This means that Mars must have accumulated a substantial quantity of light, volatile elements such as sulfur, carbon, oxygen, and hydrogen.”

This ratio of lighter elements is greater than that found within Earth’s denser core, and it could give us important hints about the differences in the formation of these neighbouring worlds.

“Somehow these light elements needed to get into the core. It may mean that the formation of Mars happened faster than Earth’s,” Stähler says. “These observations have fueled speculation that Mars might represent a stranded planetary embryo that depicts the chemical characteristics of the solar nebula located within the orbit of Mars.”

Thanks to NASA's InSight Mars mission we now have a good picture of the interior of another planet.
InSight captures an image of its landing site, which proved the ideal vantage point to observe marsquakes (NASA)

As just Knapmeyer-Endrun did, Stähler expresses some surprise regarding just how successful InSight has been in gathering seismological data, emphasising the role good fortune has played in the mission thus far.

“We were able to observe reflections of seismic waves from the core–like an echo–from relatively small quakes. And the quakes were just in the right distance from the lander. Had we landed in another location, it would not have worked out,” the seismologist says. “And the landing site was only selected because it was flat and had no rocks, so it was really pure luck.”

Stähler says that he and his team will now attempt to use seismic waves that have crossed the core of Mars to determine if the planet’s core possesses a solid-iron inner-core like Earth, or if it is entirely liquid. Just one of the lingering questions that Knapmeyer-Endrun says InSight will use marsquakes to tackle over the coming years.

“There are still multiple open questions that we’d like to tackle with seismology. For example, which geologic/tectonic features are the observed marsquakes linked to? At which depth do olivine phase transitions occur in the mantle? And Is there a solid inner core, like on Earth, or is the whole core of Mars liquid?” says the geophysicist.

And if we are to go by track record, the smart money is on InSight answering these questions and more. “Within just 2 years of recording data on Mars, this single seismometer has been able to tell us things about the crust, mantle and core of Mars that we’ve been speculating about for decades.”

Tibetan Plateau.

A shattered tectonic plate underpins the Tibetan Plateau — explaining the area’s weird earthquakes

A new geophysical model shines some light on the Tibetan Plateau’s unique geology.

Tibetan Plateau.

Natural-color image of the Tibetan Plateau.
Image credits NASA Earth Observatory.

Some 50 million years ago, India was a huge hit in Asia — quite literally, as the peninsula smashed into the continent after breaking up with Gondwana, creating the Himalayas of today. We don’t know very much about the specifics of this collision, as the Tibetan Plateau — an area at the epicenter of this collision — is quite inhospitable and hard to reach, for earth scientists and laymen alike.

New research, led by scientists from the University of Illinois at Urbana-Champaign, comes to shed more light on the event. Not only do the findings help patch our understanding of the area’s geology. The results also help explain the highly-peculiar — and very violent — seismic activity in this area.

Shaking things up

“The continental collision between the Indian and Asian tectonic plates shaped the landscape of East Asia, producing some of the deadliest earthquakes in the world,” said Xiaodong Song, a geology professor at the University of Illinois and co-author of the new study.

“However, the vast, high plateau is largely inaccessible to geological and geophysical studies.”

Song and his team drew on high-resolution seismic (earthquake) data to generate the clearest model of the Tibetan Plateau’s geology to date. They pooled together geophysical data from various studies and other sources, and collated them to generate seismic tomography images of Tibet — think of them as ultrasound imaging for geology — that peer down to about 160 kilometers under the surface.

Their work reveals that the upper mantle layer of the Indian tectonic plate is broken into four distinct pieces that push under the Eurasian plate. Each of these four fragments lies at a different distance from the origin of the tear and moves at a different angle relative to the surface than its peers. The new data match well with recorded earthquake activity, geological, and geochemical observations in the area, the team writes, which helps improve confidence in the results.

Model Tibet Plateau.

Seismic wave velocity images of the Tibetan Plateau in image a (map view) and image b (cross-section view). In image b, T1, T2 and T3 mark mantle tears, the circles indicate earthquakes deeper than 40 kilometers and the white contours show earthquake density.
Image credits Jiangtao Lia, Xiaodong Songa, (2018), PNAS.

“The presence of these tears helps give a unified explanation as to why mantle-deep earthquakes occur in some parts of southern and central Tibet and not others,” Song said.

While the Indian plate was definitely shredded after the impact, the bodies of intact crust between the tears (the four fingers themselves) are still strong enough to accumulate strain — and such strain, when released, is what causes earthquakes. At the same time, heat upwelling from the deeper mantle can pass through the torn areas more readily. Areas of crust directly above the tears become more ductile and less susceptible to earthquakes as they warm.

This last tidbit of information helps explain the “unusual locations” of some of the earthquakes in the plateaus’ southern reaches, according to co-author Jiangtao Li, who adds that “there is a striking correlation with the location of the earthquakes and the orientation of the fragmented Indian upper mantle”.

The model also helps us get a better idea of the local geology as a whole, explaining some of the area’s more peculiar surface deformation patterns, such as a series of unusual north-south rifts along the plateau, for example. Such deformation patterns, together with the location of most earthquakes in the area, further suggest that the crust and upper mantle are strongly coupled in southern Tibet — i.e. surface rocks are very well ‘glued’ to deeper formations.

Simplified model.

Idealized cartoon illustration of the tearing of the Indian plate and coupling between the crust (orange) and the mantle lithosphere (blue) in south-central Tibet. The thickness of the crust and mantle lithosphere is not to scale. The white dashed line marks the possible boundary between the underthrusting Indian crust and the overriding Himalayan orogenic prism and Tibetan crust.
Image credits Jiangtao Lia, Xiaodong Songa, (2018), PNAS.

Overall, the findings offer a clearer picture of the state of the crust and upper mantle in the Tibetan Plateau. The findings will also help us better assess areas that are at risk from earthquakes, the team adds, with the potential to safeguard lives and property from their devastating effects.

The paper “Tearing of Indian mantle lithosphere from high-resolution seismic images and its implications for lithosphere coupling in southern Tibet” has been published in the journal Proceedings of the National Academy of Sciences.

An illustration of ancient Earth's magnetic field compared to the modern magnetic field. Credit: Peter Driscoll

Earth may have had multiple magnetic poles one billion years ago

First and foremost, Earth owes its paradisiac condition to the powerful magnetic field that shields it from harmful radiation. Without this convenient field generated by a magnetic dipole there would be no plants, no bacteria, no humans — we’d be just like Mars. But it hasn’t always been this simple and stable. A new research suggests the planet went through periods of chaotic shifts in the magnetic field which lasted hundreds of millions of years. At times, more than two poles were active generating multiple, weaker magnetic fields than the one enveloping Earth today.

An illustration of ancient Earth's magnetic field compared to the modern magnetic field. Credit: Peter Driscoll

An illustration of ancient Earth’s magnetic field compared to the modern magnetic field. Credit: Peter Driscoll

The earth’s core acts like a geomagnetic dynamo. The solid inner part is constantly exchanging heat with the iron outer core, keeping it in a state of liquid motion. But the inner core was not always solid. It went through a strange period between 1 billion and 500 million years ago in which it was in a liquid state, and only began solidifying some 650 million years ago.

Peter Driscoll, a scientist at the department of terrestrial magnetism at the Carnegie Institution of Washington, was among the team of researchers who made simulations and models of Earth’s geomagnetic dynamo based on geological findings that revealed the planet’s thermal past.

“What I found was a surprising amount of variability,” Driscoll said. “These new models do not support the assumption of a stable dipole field at all times, contrary to what we’d previously believed.”

For instance, simulations suggest Earth had a dipole magnetic field one billion years ago but then transitioned to multiple poles positioned across the planet which generated weaker magnetic fields up to 650 million years ago. During this time, life may have been in a lot of trouble as it sought to adapt to varying magnetic conditions.

The implications are numerous. For one, it could change how scientists study the planet’s continental plates and ancient climate, both heavily influenced by the magnetic field.

“These findings could offer an explanation for the bizarre fluctuations in magnetic field direction seen in the geologic record around 600 to 700 million years ago,” Driscoll added. “And there are widespread implications for such dramatic field changes.”

These predictions are not the final word, though. Once these models are compared to magnetized rocks, we might be able to reach a more accurate picture.

The findings were published in the journal Geophysical Letters.

Earth’s axial tilt of 23.44 degrees gives our planet its seasons and moderates the climate. Credit: NASA

Earth rotates slower from sea-level rise: ‘Munk’s Enigma’ now solved

Earth’s axial tilt of 23.44 degrees gives our planet its seasons and moderates the climate. Credit: NASA

Earth’s axial tilt of 23.44 degrees gives our planet its seasons and moderates the climate. Credit: NASA

In 2001 a famed oceanographer called Walter Munk at the Scripps Institution of Oceanography in La Jolla, California published an important paper that discussed another facet of sea-level rise. Melting glaciers at the poles releases more liquid water into the global system, but in doing so also remove billions of tonnes of ice from the poles and transfers this mass to the equator. Physics tells us that this must slightly shift Earth’s axis and decrease the rate at which the planet spins. Munk reckoned in his paper that there must been a causal link between 20th century sea-level rise and changes in the planet’s spin. No such effect was found, puzzling scientists ever since. This is “Munk’s Enigma”.

More climate change, longer days

Earth’s rotation is gradually slowing down by around two thousandths of a second per day, which effectively lengthens the length of a day. Earlier this year, a leap second was added to maintain clocks around the world in sync. This was the second time, after 1972.

There are numerous factors that contribute to this slowdown, among which the gravity pull from the Moon which acts like a lever break. Glacier melting must also be a contributing factor, though measurements have so far eluded scientists. Now, a team of researchers from Canada and the U.S. think they’ve cracked the puzzle.

“If you melt ice sheets or glaciers, which happen to be close to to the poles, and all of that mass moves from the poles toward the equators, that movement is very similar [to] a figure skater who puts her arms out,” said the new paper’s lead author, Jerry Mitrovica, a professor of geophysics at Harvard University. “The melting of glaciers acts to slow the spin of the Earth in a measurable way.”

“The rise of sea level and the melting of glaciers during the 20th century is confirmed not only by some of the most dramatic changes in the Earth system — for example, catastrophic flooding events, droughts heat waves — but also in some of the most subtle — incredibly small changes in Earth’s rotation rate,” Mitrovica added.

Mitrovica and  Sabine Stanley, a professor of physics at the University of Toronto, claim that they have evidence that suggests sea-level rise does in fact slowdown Earth’s rotation. What eluded Munk in the first place were some wrong assumptions: 1) more precise measurements show glacier melting is about 30% less severe than Munk assumed 2) Munk used a faulty model of Earth’s internal structure 3) the interaction between Earth’s rocky mantle and the planet’s molten metal outer core was discounted. This last point proved to be very important.

“The earth itself is made up of a solid layer with this liquid core inside,” Stanley said. “Whenever motion occurs in one layer, that’s going to affect the other layer.”

She went on to explain how this is akin to a hamster’s wheel. When the pet runs in one direction, the wheel spins in the opposite direction. This is the coupling effect.

“We know that there have been changes in the magnetic field to suggest changes in the core’s rotation, and that means changes in the way we see things on the surface,” Mitrovica said.

At the end, the researchers came up with neat calculations that confirm ongoing glacial melting and the resulting sea-level rise are affecting the Earth in ways that match theoretical predictions, but also empirical data like astronomical and geodesic data.

“What we believe in regard to melting of glaciers in the 20th century is completely consistent with changes in Earth’s rotation measured by satellites and astronomical methods,” Mitrovica said. “This consistency was elusive for a few years, but now the enigma is resolved.

“Human-induced climate change is of such pressing importance to society that the responsibility on scientists to get things right is enormous,” Mitrovica added. “By resolving Munk’s enigma, we further strengthen the already-strong argument that we are impacting climate.”

Thermal scans reveal interesting anomaly in Great Pyramid

Archaeologists believe that we’ve discovered most of what lies in the Valley of Kings in Egypt, but that doesn’t mean we’ve discovered everything. Even inside the Great Pyramid of Giza, outside of Cairo, researchers have found something interesting.

If you look at it, the size and orientation doesn’t seem to indicate a tunnel. Image credits: HIP INSTITUTE/PHILIPPE BOURSEILLER

After conducting thermal scans, researchers reported rather strange heat spots across the pyramids, especially a particularly large patch. Rocks (and all materials) hold heat differently to air, so this patch could signify some major cracks, a void, or perhaps even a passage under the pyramid.

Antiquities Minister Mamdouh El-Damaty said that especially one patch is interesting:

“There is something like a small passage in the ground that you can see, leading up to the pyramid’s ground, reaching an area with a different temperature,” said El-Damety. “What will be behind it?”

HIP INSTITUTE/PHILIPPE BOURSEILLER

There are already some assumptions about what it could be, but there is really not enough information to be certain. A void or an entirely different construction material seem like the most plausible options. Realistically speaking, this is more likely to help us better understand how the pyramids were built, rather than finding a secret tunnel.

“At the very least, this anomaly will shed additional light on the construction techniques of the 4th dynasty Egyptians,” Egyptologist Beth Ann Judas said in an interview. “It’s rather exciting actually. Over the past few years, archaeologists have been learning more about the workmen and officials who are connected to the pyramids, and this gives us more information about their work.”

Thermal imaging is actually not a common technique used in archaeological imaging. Ground Penetrating Radar (GPR) and magnetometry are used more often in this context. GPR has already revealed some interesting potential cavities/voids, and it will be interesting to see if these correlate with the thermal scans.

This study, called Scan Pyramids will continue until the end of 2016, and thermal scanning is just the first step. They will also use infrared to survey the pyramids, and implement even more exotic techniques, such as using cosmic particles called radiographic muons and 3D reconstruction to try to map the secrets within the pyramids. If there’s something left to be found under the pyramid, they’ll find it… probably.

MIT Wi-Fi technology can see you through walls

Researchers at MIT have developed a device that can track human silhouettes behind walls using Wi-Fi. The device called RF-Capture emits out Wi-Fi signals and then tracks back the reflections and see if together, they piece a human form.

This is what the RF-Capture “sees”. Note that it only detects some parts of the human body. Image credits: MIT.

Wi-Fi is a local area wireless computer networking technology that allows electronic devices to connect to each other, generally using the 2.4 gigahertz (12 cm) UHF and 5 gigahertz (6 cm) SHF ISM radio bands. But Wi-Fi can do more than create networks and connecting you to the internet – as a new study just showed, it can send out a signal and reconstruct what’s “on the other side” – see what reflected the signal back. This can generally be done with every type of wave, but high frequency waves provide better resolution and Wi-Fi is a cheap and generally available technology, which makes it more attractive to use.

Here’s how this works: RF-Capture is placed in a room, and starts emitting signals; a part of the signal bounces back off the walls, but some of it passes through and gets to the neighboring room. If someone is walking in the neighboring room, then the signal is again reflected by the human body and returns to the Wi-Fi device; only some of the body parts create significant reflections. The technology could be used in the houses of elder people or people with disabilities to see if they have fallen or if they are injured and need help. It can also be used in smart homes, to detect movements that control the appliances in the house. It can identify people and see if they are making certain gestures. Here’s a video showing how it works:

How it works. Image via MIT.

The sensibility is absolutely amazing! Being able to detect movements with the same accuracy as a kinect camera placed right in front of the subject is absolutely spectacular.

The concept itself is not new – it’s something that has been used in geophysics for decades, for example in ground penetrating radars, a technology that can detect buried near-surface objects. But the application is entirely different, and holds a lot of potential, because Wi-Fi is basically ubiquitous in the developed world.

Earth’s gravity pull is opening cracks and faults on the Moon

Just as the Moon is causing waters on Earth to go up and down (tides), so too does the Earth affect the Moon. Recently, researchers have found that our planet’s gravitational pull is having a deep effect on our satellite, opening new cracks and faults on its surface.

Lunar Reconnaissance Orbiter Camera images have revealed thousands of young, lobate thrust fault scarps on the moon. Image released Sept. 15, 2015.
Credit: NASA/LRO/Arizona State University/Smithsonian Institution

“We know the close relationship between the Earth and the moon goes back to their origins, but what a surprise [it was] to find the Earth is still helping to shape the moon,” study lead author Thomas Watters, a planetary scientist at the Smithsonian Institution’s National Air and Space Museum in Washington, D.C., told Space.

They analyzed data from NASA’s Lunar Reconnaissance Orbiter (LRO), which launched in 2009 – there’s an abundance of data from the LRO that is yet to be properly analyzed. They discovered 14 lobe-shaped fault scarps, or cliffs. These are among the most common geological features on the planet, likely forming as the hot interior cooled and contracted, causing the solid crust to crack.

However, if the only factor creating these cracks was the Moon’s interior cooling down, then you’d expect their orientation to be random; however, they are anything but random.

“It was a big surprise to find that the fault scarps don’t have random orientations,” Watters said. Instead, “there is a pattern in the orientations of the thousands of faults, and it suggests something else is influencing their formation, something that’s also acting on a global scale,” Watters said in a statement. “That something is the Earth’s gravitational pull.”

Basically, they found that most scarps are oriented where the Earth’s pull is the strongest. Many are lined up north to south at low and mid latitudes near the moon’s equator and east to west at high latitudes near the moon’s poles – either in the closest areas to the Earth, or the farthest ones away. When they created a model to take Earth’s gravity into account, it closely match the observed data.

“With LRO, we’ve been able to study the moon globally in detail not yet possible with any other body in the solar system beyond Earth, and the LRO data set enables us to tease out subtle but important processes that would otherwise remain hidden,” John Keller, LRO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a different statement.

It’s quite possible that these cracks are active right now, opening from time to time due to the Earth’s attraction. If this is the case, then there are likely “moonquakes”, which a network of seismometers could one day pick up.

Stonehenge was actually the core of a huge spiritual centre

We tend to think of the Stonehenge as a lone giant, huge blocks of rock towering over the quiet British landscape. But as a new study has revealed, Stonehenge was likely a diverse and vibrant place, a complex of different religious and cultural settings.

 

Source: Ludwig Boltzmann Institute, Birmingham.

Painting Stonehenge in New Light

Using geophysical techniques (mostly Ground Penetrating Radar – GPR – and magnetometry), scientists managed to get an unprecedented view of the underground surrounding Stonehenge. They’ve basically “sliced” the ground up to 4 meters deep, and located buried remains with unprecedented resolution. Most spectacularly, they discovered a 330-metre long line of more than 50 massive stones, buried under part of the bank of Britain’s largest pre-historic henge.

“Up till now, we had absolutely no idea that the stones were there,” said the co-director of the investigation Professor Vince Gaffney of Birmingham University.

The c-shaped enclosure – more than 330 metres wide and over 400 metres long – faced directly towards the River Avon, and even though the rocks are now horizontal, it seems likely that they were initially vertical, standing stones. But this fallen monument isn’t the only surprising thing they found. Archaeologists also report a 33 meter (108 feet)-long timber building dated at about 6,000 years old, likely used for rituals and spiritual practices. It’s possible that the timber building was there before Stonehenge was even built.

“[The building] has three rows of roof-bearing posts. It is around 300 square metres and slightly trapezoidal, which is interesting because in the same period on the continent, about 100 to 200 years earlier, we also find this type of trapezoidal building related to megaliths [giant stones],” noted Wolfgang Neubauer of the Ludwig Boltzmann Institute.

Image via BBC.

 

They also report several Neolithic and Bronze Age religious shrines between 10 and 30 meters ( 32 to 100 feet) in diameter and Bronze Age burial mounds as well as four Iron Age shrines or tombs, and a half dozen Bronze Age and Iron Age domestic or livestock enclosures.

 

Archaeological features, as seen with magnetic prospection. Image via BBC.

It took four years of painstaking work and a lot of data integration, processing and analysis before we can finally say Stonehenge wasn’t a lonely desolate place.

“It shows that, in terms of temples and shrines, Stonehenge was far from being alone,” said Professor Gaffney.

Sticks and Stones

Computer rendering of the overall site. Image via Wikipedia.

Located 8 miles (13 km) north of Salisbury in England, Stonehenge represents the remains of a ring of standing stones set within earthworks. It is in the middle of the most dense complex of Neolithic and Bronze Age, dating anywhere from 3000 to 2000 BC. Radiocarbon dating in 2008 suggested that the first stones were raised between 2400 and 2200 BC, whilst another theory suggests that bluestones may have been raised at the site as early as 3000 BC – it’s still a matter of debate in the scientific community, but everyone agrees that the building process was lengthy and took place in several stages.

Stonehenge was used as a burial place. In, 2013 a team of archaeologists, led by Mike Parker Pearson, excavated more than 50,000 cremated bones of 63 individuals buried at Stonehenge. Now, more and more evidence is indicating that there is more to the Stonehenge area than previously believed.

There is little or no direct evidence for the construction techniques used by the Stonehenge builders. Over the years, various authors have suggested some conspiracy theories, claiming that supernatural or futuristic methods were used, usually asserting that the stones were impossible to move otherwise. However, that’s not true. It’s been demonstrated that conventional techniques and Neolithic technology as basic as shear legs can be effective at moving and placing rocks of that size and weight.

Geophysics and Archaeology

It may come as a surprise to most people, but in modern times, archaeological explorations have less to do with digging, and more to do with remote surveying technology – geophysics. In archaeology, geophysical survey is ground-based physical sensing techniques used for archaeological imaging or mapping. Remote sensing and marine surveys are also used in archaeology.

Basically, geophysical surveying creates underground maps of subsurface archaeological features; it measures a parameter of the underground (for example resistivity or magnetic susceptibility) and detects buried features when their physical properties contrast measurably with their surroundings. The most common methods are:

  • magnetic prospection; usually the fastest method, devices called magnetometers measure the total magnetic field strength, or they may use two (or more) separated sensors to measure the gradient of the magnetic field (the difference between the sensors). This method can detect most archaeological features, as every kind of material has unique magnetic properties, even those that we do not think of as being “magnetic.”
  • electrical prospection; at the very basic level, electrometers work as Ohmmeters used to test electrical circuits. In most systems, metal probes are inserted into the ground to obtain a reading of the local electrical resistance. A stone foundation might impede the flow of electricity, while the organic deposits within a midden might conduct electricity more easily than surrounding soils – this usually can detect structures, but not individual artifacts.
  • ground penetrating radar (GPR); perhaps the most well known method, although not the most used. It basically works like the name says – it’s a radar that penetrates the ground and shows you what’s underneath, to some extent. It generally has the best resolution of all methods, but is also susceptible to sources of “noise” – any signal that might block valuable information.

These three methods, as well as a 3D laser scanner was used for this study.

To me, it’s simply spectacular how very different branches of science can work together and achieve such spectacular results. Just think about it for a moment: without having to actually dig anything, we know that there is an intricate social, cultural and religious complex around the Stonehenge, and we know what kind of activities people did there. Isn’t that just mind blowing?

Major Viking Hall Identified in Sweden

A major Viking hall measuring over 50 metres in length has been identified near Vadstena in Sweden. Archaeologists from Stockholm University and Umeå University used non-invasive geophysical techniques to identify the hall, and they have a very good idea how it looked like, even without  actually digging it.

The hall, as viewed with geophysical methods. Image credits: Andreas Viberg.

The Viking Age is the period from 793 AD to 1066 AD in European history, especially Northern European and Scandinavian history. Vikings were excellent seafarers, roaming the northern and western seas of Europe both in commercial and military enterprises.

This huge hall was found on the Aska barrow, which was long thought to be a burial mound because of its structure. Archaeologists have now revealed that this was actually the foundation of a very large building, a hall probably ruled by a royal family; this theory is supported by previous excavations, which uncovered some royal tombs in the vicinity of the hall.

“Parallels are known from several of the era’s elite sites, such as Fornsigtuna near Stockholm and Lejre near Roskilde. The closest similarities are however seen in a recently excavated feasting hall at Old Uppsala near Stockholm. Such close correspondences suggest intensive communication between the two sites”, says Martin Rundkvist of Umeå University.

The building was over 50 meters long and about 14 meters wide, equipped with double walls and four entrances. The measurements also indicate a large fireplace at the centre of the floor, which is a clear sign that this was a significant hall, and no ordinary building.

Using ground-penetrating radar to detect underground structures. Photo: Martin Rundkvist.

The study was conducted using geophysical methods – more specifically, a technique called ground penetrating radar. Ground Penetrating Radar (GPR) uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band and detects the reflected signals from subsurface structures, basically creating a map of the underground. In modern archaeology, it is very important to detect structures without having to actually dig them. This not only saves a lot of time and money, but it also helps preserve these wonders instead of potentially destroying them during the excavation.

“Our investigation demonstrates that non-invasive geophysical measurements can be powerful tools for studying similar building foundations elsewhere. They even allow scholars to estimate the date of a building without any expensive excavations”, says Andreas Viberg of the Archaeological Research Laboratory at Stockholm University who directed the fieldwork.

Journal Reference:

  1. Martin Rundkvist and Andreas Viberg. Geophysical Investigations on the Viking Period Platform Mound at Aska in Hagebyhöga Parish, Sweden.Archaeological Prospection, 2014 DOI: 10.1002/arp.1500

Everything you need to know about England’s ‘hidden medieval city’, Old Sarum

It’s one of England’s better kept secrets – Old Sarum is a hidden gem among gems, one of the most spectacular ancient sites in Europe and in the world. Old Sarum is the site of the earliest settlement of Salisbury in England. The site contains evidence of human habitation as early as 3000 BC, but only now have archaeologists uncovered the network of buildings in the city, including a very large and imposing castle.

Artist’s impression of barons swearing allegiance to William the Conqueror in 1086. Image via English Heritage.

Using top notch geophysical techniques, a research team of students and academics from the University of Southampton carried out a survey on the site, scanning the underground and detecting buried structures. They located numerous structures on the inside and outside of the fortification, but what they found in the center is absolutely stunning: a 170m long, 65m wide palace complex, which has walls 3m thick and is arranged around a large courtyard, surrounded by many significant houses. Basically, this finding shows archaeologists and historians where major political and religious centre was in Norman Britain. The investigations revealed a settlement including structures from the late 11th century, contemporary with the construction of a cathedral and castle. The city was inhabited for over 300 years, but then abandoned, as the people moved to New Sarum (today’s Salisbury).

Professor David Bates of the University of East Anglia, a leading authority on Norman England said that this discovery is of enormous importance:

“It reveals the monumental scale of building work taking place in the earlier 12th century,” he said.

Old Sarum, aerial view. Image via English Heritage.

Old Sarum, aerial view. Image via English Heritage.

Indeed, because the city was inhabited for only three hundred years and then abandoned, the site is pristine; there is no “contamination” – later structures built on top of the older ones. Also, the city was a major one, so it has all the buildings and structures you would hope to find in a city from that period. Among the findings, archaeologists report:

  • The major castle, the biggest “unknown” castle in the UK
  • A series of massive structures along the southern edge of the outer bailey defensive wall, probably defensive structures
  • An open area of ground behind these large structures, perhaps used to muster troops for these structures
  • Several large residential areas
  • Evidence of deposits indicating industrial features, such as kilns or furnaces
  • Evidence of rock quarrying.

Basically, they put up an entire plan of the city. Kristian Strutt of the University of Southampton, the archaeologist leading the geophysical survey, added:

“Archaeologists and historians have known for centuries that there was a medieval city at Old Sarum, but until now there has been no proper plan of the site. Our survey shows where individual buildings are located – and from this we can piece together a detailed picture of the urban plan within the city walls.”

The research was conducted as part of the Old Sarum and Stratford-Sub-Castle Archaeological Survey Project, directed by Kristian Strutt and fellow Southampton archaeologists Timothy Sly and Dominic Barker. In order to conduct the geophysical underground mapping, they conducted magnetic, electrical and ground penetrating radar (GPR) measurements. These are all non-invasive techniques, and allow archaeologists to know what they’re dealing with without actually seeing it.

Archaeologists were able to create an underground map of Old Sarum without having to dig, through geophysical surveying. Image via Southampton University.

The Old Sarum site is under the custodianship of English Heritage, who allowed them to conduct the researchHeather Sebire, Property Curator at English Heritage, comments:

“Having the team of archaeologists on site over the summer gave our visitors a chance to find out more about how important historic landscapes are surveyed. The use of modern, non-invasive surveying is a great start to further research at Old Sarum. From this work we can surmise much about the site’s past and, whilst we can’t conclusively date the findings, it adds a new layer to Old Sarum’s story. We welcome the chance to find out more about our sites, and look forward to exploring ideas for further research in the future.”

Old Sarum was originally an Iron Age fort established around 400 BC and occupied by the Romans after the conquest of Britain in AD 43. The city continued to grow and thrive, and in 1092, a cathedral was already constructed. Archaeologists hope to return again in 2015 and conduct even more detailed measurements. In the meantime, they will have to evaluate and analyze their current results, which paint an extremely detailed picture of ancient British society.

Ancient Magma found on the Moon, below the Dark Spots

Scientists have discovered an almost rectangular feature consisting of ancient magma. The features are similar to rifts here on Earth, a linear zone where the Earth’s crust and lithosphere are being pulled apart. However, since the Moon doesn’t have any plate tectonics to cause rifts, the origin of this magma is still questionable.

Magma on the Moon

uried rift features, detected through gravity mapping, are seen superimposed on a full moon. Image credits: KOPERNIK OBSERVATORY/NASA/COLORADO SCHOOL OF MINES/MIT/JPL/GODDARD SPACE FLIGHT CENTER

Several kilometers below the Moon’s biggest dark spot, Oceanus Procellarum, scientists have discovered a perimeter thought to be the remnants of a geological plumbing system that spilled lava across the moon about 3.5 billion years ago. The existence of such features indicates that early in its history, the satellite was much more active geologically, with significant volcanic and tectonic activity.

“We’re realizing that the early moon was a much more dynamic place than we thought,” says Jeffrey Andrews-Hanna, a planetary scientist at the Colorado School of Mines in Golden and lead author of a new study of the Procellarum’s geology. The discovery also casts doubt on the decades-old theory that the circular Procellarum region is a basin, or giant crater, created when a large asteroid slammed into the moon. “We don’t expect a basin rim to have corners,” Andrews-Hanna says.

Oceanus Procellarum (Latin for “Ocean of Storms”), is a vast lunar mare on the western edge of the near side of Earth’s Moon. Lunar mares were mistaken for actual seas by ancient sky gazers, but we now know that they are in fact large, dark, basaltic plains formed by ancient volcanic eruptions. The maria (plural for mare) cover about 16 percent of the lunar surface, but only Oceanus Procellarum is large enough to be called an “ocean”.

Gravimetric Measurements

A gravitational map made from the GRAIL data (Image: NASA)

These features were revealed by gravimetric measurements using the data gathered by GRAIL (Gravity Recovery and Interior Laboratory). The GRAIL mission also enabled the development of a gravity map of the Moon before being crashed down to the lunar surface. Gravimetry is the measurement of the strength of a gravitational field. The method has been used for many decades on Earth in various projects (finding oil basins, subterranean holes, metallic ore etc).

Much like the devices used on Earth, GRAIL is very sensitive to tiny variations in the Moon’s gravity. Using data gathered by the satellite, researchers can then infer density variations beneath the surface. Below known impact basins, GRAIL found the typically associated ringlike patterns. However, under Procellarum, they observed a mysterious rectangle with heavier density.

“It was a striking pattern that demanded an explanation,” Andrews-Hanna says

Interpreting the results is no easy feat. In a study published today in Nature, the researchers propose that these initial cracks eventually grew into rift valleys, where magma from the moon’s mantle welled up and pushed apart blocks of crust – something completely unrelated to impact basins. The “extra density” is likely caused by magma, which is heavier than the Moon’s crust.

“The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin”, researchers write in the study.

The rifts of Oceanus Procellarum as revealed by gravitational anomalies. Image via NASA.

They propose that the extra weight would have caused the whole region to sink slightly making it look more like a basin. Herbert Frey, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland is convinced by this study – and excited for future studies on the Moon’s past.

“It just means the moon continues to surprise us,” he says.

Journal Reference: Jeffrey C. Andrews-Hanna, Jonathan Besserer, James W. Head III, Carly J. A. Howett, Walter S. Kiefer, Paul J. Lucey, Patrick J. McGovern, H. Jay Melosh, Gregory A. Neumann, Roger J. Phillips, Paul M. Schenk, David E. Smith, Sean C. Solomon & Maria T. Zuber. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data. Nature 514, 68–71 (02 October 2014) doi:10.1038/nature13697

This aerial photograph shows patchmarks whose position suggest there were once laid stones there. Photo: English Heritage

Stonehenge may have once been a complete circle

This aerial photograph shows patchmarks whose position suggest there were once laid stones there. Photo: English Heritage

This aerial photograph shows patchmarks whose position suggest there were once laid stones there. Photo: English Heritage

Stonehenge is one of Britain’s greatest national treasure, but while magic, myth and mystery surrounding the monumental site has been time and time again dispelled by science, there is still much to learn. One major debate regarding Stonehenge is whether or not the site once formed a complete circle. Now, a short hosepipe and a scientist’s keen eye might settle the issue once and for all: the monolithic complex indeed closed a circle.

Going in circles

More than nine hundred stone rings exist in the British Isles, and scholars estimate that twice that number may originally have been built. Scholars usually classify these types of megalithic structures as rings rather than circles, because the rough proportions for the different shapes are 2/3 true circles, 1/6 flattened circles, 1/9 ellipses, and 1/18 eggs. Stonehenge, however, is roughly circular.

The Wiltshire monument was likely built in several stages with “the unique lintelled stone circle being erected in the late Neolithic period around 2500 B.C.,” according to the English Heritage. The site is comprised of massive central trilithons, smaller bluestone settings, sarsen circle capped by lintels, outer bank and ditch. For centuries scientists have investigated Stonehenge, but the passing of many years since it was last used as a site of worship and astrology had left it marks. The debate still ranges on whether part of the site was left intentionally incomplete or whether it was once complete to describe a full circle.

One dry summer in 2013 may have helped shed light on the matter. Tim Daw, an English Heritage steward, observed marks of parched grass in an area that had not been watered (the hosepipe was too short to reach it). Upon closer inspection, Daw found these marks appeared in the sarsen circle exactly where stones were expected to stand.

In places where stone structures or holes used to be, vegetation grows differently than that in its vicinity. That’s because most often than not buried or once-buried structures interfere with soil permeability, so plants growing on top develop in a characteristic manner.

“Plants that may have initially benefited from the easily available rooting and moisture in disturbed ground fail as the soil dries out, whilst the shorter-rooting surrounding plants manage to survive by extracting water directly from the porous chalk,” Daw and colleagues wrote.

The researchers involved immediately launched a survey using Differential Global Positioning System technology, however due to time constraints the equipment couldn’t be deployed during the same conditions when the parched grass marks were first encountered.

“Ideally the survey would have differentiated between marks caused by parching –- the majority -– and those caused by lusher growth,” Daw and colleagues wrote.

“It would have also have graded the marks into ‘definitive’, ‘probable’ and ‘possible’ categories. This was not possible, and the result must therefore be treated with caution,” they added.

The English Heritage hopes to access historical aerial photography from summer seasons and schedule surveys when the weather is right. Where digs and geophysical methods failed to miss this highly important Stonehenge piece, the growth of a simple parched grass may have helped reveal what was under debate for centuries. You just have to keep your eyes opened.

Findings appeared in the journal Antiquity.

Project drills deep in New Zealand to understand and predict earthquakes

For the first time, geophysicist in New Zealand will place seismic sensors deep into a geological fault to record the build-up and occurrence of massive earthquakes, potentially giving crucial  information about one of the biggest faults in the world.

It’s hard to say anything after such an insightful and well explained video. The Alpine Fault runs for about 600 kilometres along the west coast of South Island, marking the boundary between the Pacific and Australian tectonic plates. It is a planar discontinuity over a huge volume of rock, across which there has been significant displacement – see the mountains.

Every year, the two tectonic plates slide by each other by about 2.5 centimeters; it may not seem like much, but just think of the incredibly massive volumes which are sliding this way, creating friction and building up pressure – and just think what the effects will be over hundreds of years. Geologists are confident that the fault is “ready to break in its next earthquake” — with a 28% chance of a rupture in the coming 50 years, which is another reason why this project is so important.

“If we go on to record the next earthquake, then our experiment will be very, very special,” says Rupert Sutherland, a tectonic geologist at New Zealand’s Institute of Geological and Nuclear Sciences in Lower Hutt, and one of the project’s leaders. “A complete record of events leading up to and during a large earthquake could provide a basis for earthquake forecasting in other geological faults.”

The costs of the project are $2 million, which are not that high when you consider the potential implications. The first step is to collect geological samples, then dig a shallow borehole and insert sensors into it. The hole will then be deepened and strengthened, and after this, more seismic sensors will be added. This will hopefully be done by December. Then, the data will be directly analyzed and inserted into computer models of faults, in order to better understand when and how faults break, and how this is foreshadowed.

For example, one idea is that large differences in groundwater pressures on either side of the fault zone could indicate that a big quake is imminent.

“The fault appears to currently form an impermeable barrier, and it’s likely that time-dependent differences in groundwater pressure on either side of the fault play a role in governing earthquake nucleation processes and the radiation of seismic waves,” says John Townend, a seismologist at Victoria University of Wellington, who is part of the project.

Frozen underworld discovered beneath Greenland Ice sheet

The former popular landscape was an expanse of warped shapes, out of which some were as tall as a Manhattan skyscraper, and it was discovered by an ice-penetration radar loaded aboard NASA survey flights.

According to the scientists who made the discovery, this could deepen the level of understanding concerning the way in which the ice sheets of Greenland and Antarctica respond to climate change. Until recently, the scientific community believed that the the shapes they discerned beneath the ice sheet were nothing else but mountain ranges, according to the specialists studying the Greenland ice sheet for evidence of change under the circumstances of global warming.

Everything was just flat, parallel lines. This is how the ice is supposed to be. But here it is breaking all the rules. You get these crazy, folded, distorted, overtuned, undulating things at the bottom of the ice, and they are the size of skyscrapers’, declared Kirsty Tinto, geophysicist at Lamont-Doherty.

It was the new technologically advanced new gravity-sensing and radar operating from NASA’s airborne surveys of the ice over the last 20 years how the scientists got to the conclusion that the formations they had identified were not rock, but ice.

The melting and subsequent re-freezing of water at the bottom of the ice sheet is what caused the formations, as stated by the scientists – who were really surprised by their results. It’s even more surprising that these new-found structures, some of them measuring up to 1 meter thick, cover approximately 10 per cent of the surveyed areas of Northern Greenland.

c82ee04d-8cbe-49fc-89e6-34a627fa42a5-460x245

Around Petermann glacier in north-western Greenland there were found circa a dozen formations, which has caused fast changes, given that two years ago they calved an iceberg twice the size of Manhattan – but the melting and re-freezing at the bottom of the ice has been happening for thousands of thousands of years, according to the scientists. While the scientists were informed of such a process, what they didn’t know until now was that the melt-water was re-freezing into more complex formations.

The melt-water is a result of the glacier warming under its own weight, and it freezes and grows up into the forms from around its base.

We see more of these features where the ice sheet starts to go fast. We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow,’ declared Robin Bell, lead author of the study and geophysicist at Columbia University’s Lamont Doherty Earth Observatory.

The process appears to accelerate the flow of glaciers, according to Bell, but Tinto said that further research was needed in order to prove this hypothesis.

If we want to understand how ice is going to respond to climate change, we have to understand its fundamental dynamic. It is not just that you are melting the surface and the surface is just running into the sea. There is a complicated and quite beautiful system running through the ice and you have to understand it top to bottom to understand what it is doing”, said Tinto.

New wireless network will revolutionize soil testing

A researchers from the University of Southampton has developed a a wireless network of sensors that is set to revolutionize soil-based salinity measuring.

Testing the salinity levels in soils is a big deal – any salty water infiltrations can have massive effects on agriculture and sometimes, even on soil stability. At the moment, you can analyze soil salinity either indirectly, through geophysical techniques (most notably resistivity measurements, as salty water is extremely conductive), or directly – by taking soil samples and analyzing them in the lab. The problem is that resistivity only maps any salty infiltrations, without giving some clear values, while sampling takes a lot of time and money.

Dr Nick Harris, from Electronics and Electrical Engineering, worked with a group of professors from the University of Western Australia (UWA) to produce the revolutionary sensor that can carry out non-invasive measurements handily.

The sensor basically measures the chloride (salt) in the soil moisture; by linking several sensors together, he can create a wireless network that can collate and relay the measurement readings. The network can also control the time intervals at which measurements are taken in order to develop a time map.

Dr Harris says:

“Traditionally, soil-based measurements involve taking samples and transporting them to the laboratory for analysis. This is very labour and cost intensive and therefore it usually means spot checks only with samples being taken every two to three months. It also doesn’t differentiate between chloride in crystallised form and chloride in dissolved form. This can be an important difference as plants only ‘see’ chloride in the soil moisture. The removal of a soil sample from its natural environment also means that the same sample can only be measured once, so the traditional (destructive) method is not suited to measuring changes at a point over a period of time.”

The network also employs a small unit which is “planted” in the ground and just left there, and the limiting factor for the entire array is the lifetime of the sensor – which is estimated to be well in excess of 1 year. The battery-powered unit sends the data via either short range radio, Bluetooth, satellite or mobile phone network, and it also allows it to be stored on a memory card and be collected at a later time.

“These soil-based chloride sensors can benefit a wide range of applications. Large parts of the world have problems with salt causing agricultural land to be unusable, but the new sensors allow the level of salt to be measured in real time, rather than once every few months as was previously the case.”

The good thing is that you can also plant these sensors at different depths and have an accurate 3D image of what is happening with the underground salty water. He believes that the sensors can be used at a local levels by farmers, but also at a much larger scale – when planning irrigations or development strategies, for example.

“At plant level, probes can be positioned at continuous levels of depth to determine the salt concentration to which roots are exposed and whether this concentration changes with the depth of the soil or in different weather conditions. We can also measure how well a plant performs at a particular concentration and change the salt content for a few days and observe the effects. On a bigger scale, sensors could be placed at different locations at catchment scale to observe any changes in the level of salinity within a field over time, having a direct impact on irrigation strategies. We have already been able to make some interesting observations on real world chloride concentration changes over just 24 hour periods, illustrating the dangers of relying on single point, single time measurements.”

Mobile US seismic array maps American mantle

A laudable, ambitious initiative is nearing fruition: the US$90-million Transportable Array, a moveable grid of seismometers that blankets America.

Since 2004, the set of 400 seismometers, loaded on trucks, have gradually marched, from the Pacific coast across the Rocky Mountains and the Great Plains and is finally reaching the eastern coastline. Whenever they arrive at the specified location, scientists dig holes and bury instruments in plastic cases. The project’s purpose is to establishe the best picture yet of the mantle beneath the North American continent.

earthscope2

Source: IRIS.

Reaching a few hundred kilometers beneath the surface, the array analyzes how natural waves from earthquakes move in the mantle and the crust, painting the most accurate picture so far. The array works similar to a CT scan – moving across the surface and gathering information from more and more points.

“As the array has moved, the whole picture of what’s under North America has gotten much sharper,” says Andy Frassetto, a seismologist at the Incorporated Research Institutions for Seismology (IRIS) in Washington DC, which operates the stations.

Having almost finished their work in 48 states, they are now heading over to Alaska, where the toughest challenge awaits. The Transportable Array, along with other permanent and temporary seismic stations, is one of three cornerstones making up the larger EarthScope initiative. EarthScope is an earth science program using geological and geophysical techniques to explore the structure and evolution of the North American continent and to understand the processes controlling earthquakes and volcanoes. The EarthScope initiative has three components – the seismometers are just the first one. The second one is a set of GPS that measure tiny movements in the Earth’s crust, and the third one is a 3.2-kilometre-deep hole drilled into California’s San Andreas fault – but this step experienced a big setback when instruments lowered down the hole stopped working after just days for an unknown reason. But the first two initiatives more than made up for that:

“We’ve learned a lot more by integrating things together than we would have by doing them separately,” says Robert Smith, a geophysicist at the University of Utah in Salt Lake City, and an early leader of EarthScope.

Source: IRIS.

Source: IRIS.

Researchers are now eagerly waiting for the equipment to arrive in Alaska, which will provide some of the most valuable data from all the country. Alaska’s geology is interesting to say the least, with the the Pacific crustal plate slamming into and diving under the continent. But even with this spectacular tectonic development, little has be done to improve our understanding of the area – in part because the state is so big and it costs a lot to probe all of it, and partially because of the rough conditions.

“We have sort of a ‘zeroth’ order of understanding,” says Rick Saltus, a USGS geophysicist in Denver. Now, he says,“we’ll get the first order”.

Geophysicists find a layer of liquefied rock in the Earth’s mantle that acts as a lubricant for tectonic plates

Scientists at Scripps Institution of Oceanography at UC San Diego have found a layer of liquefied molten rock in Earth’s mantle that may be acting as a lubricant for the sliding motions of the planet’s tectonic plates. This discovery has very far reaching implications, which can solve some of the long standing geological puzzles, as well as lead to a better understanding of earthquakes and volcanism.

Electromagnetic measurements

plate tectonics1

They used a relatively common, but uniquely improved geophysical technique (magnetotellurics), which involved advanced seafloor electromagnetic imaging technology. They imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves underneath Central America. They basically deployed a vast array of seafloor sensors that monitor the natural electromagnetic signals to map features of the crust and mantle. Back in 2010, they started noticing something was weird – they were finding magma in unexpected places.

cocos plate 2

“This was completely unexpected,” said Key, an associate research geophysicist in the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps. “We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren’t expecting to find at all-it was pretty surprising.”

cocos plate

The marine electromagnetic technology employed in the study was originated by Charles “Chip” Cox, an emeritus professor of oceanography at Scripps, and further improved by Constable and Key. The method has been so successful, that since 2000, they have been working with big oil companies to map out offshore oil and gas reservoirs.

The planetary engine

Plate tectonics is, if you will, the backbone of modern geology and geophysics. It is not perfect, by any standards, but it is a good theory that describes the large-scale motions of Earth’s lithosphere; one thing that’s been puzzling is the exact forces and mechanisms that allow the planet’s tectonic plates to slide across the earth’s mantle; one theory was that as minerals go deeper in the mantle, the water they contain is ejected, and this results in a more ductile mantle that would facilitate tectonic plate motions. However, no clear data has been provided to confirm or infirm this theory.

“Our data tell us that water can’t accommodate the features we are seeing,” said Naif, a Scripps graduate student and lead author of the paper. “The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle and that’s really what’s creating this ductile behavior for plates to slide.”

Indeed, if there isn’t some major flaw with this study, then it could pretty much change the way we view this sliding mechanism.

tectonics lubricant

The orange area inside the dashed lines is the lubricant layer which facilitates the plate motion. The blue areas represents the Cocos plate subducting beneath the central American continent, and the black points are the earthquakes.

“This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes,” said Bil Haq, program director in the National Science Foundation’s Division of Ocean Sciences.

To get to the conclusion that there is a layer which acts as a lubricant, they studied the fluid content of the subducting plate offshore Nicaragua and Costa Rica. Magnetotellurics and controlled source electromagnetics imaged the porosity variations associated with lithospheric bending and cracking near the trench, as was suggested by a previous reflection seismic imaging. Analyzing the obtained parameters, they modeled this lubricant layer.

Their results, if valid, could help geologists better understand the genesis of some earthquakes, as well as some questions unanswered for decades.

“One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes,” said Key.

Now, the next step is to figure out how exactly is this layer formed and the source that supplies this magma.

Via Scripps Research Institute

Ancient, long-lost continent found under the Indian Ocean

Evidence of drowned remnants of an ancient microcontinent have been found in sand grains from the beaches of a small Indian Ocean island, according to a new research.

Zircons and volcanoes

mauritia

This evidence was found in Mauritius, a volcanic island 900 kilometres east of Madagascar which serves as an exotic destination for many tourists. Basaltic rocks from the island have been dated to approximately 9 million years ago, but now, an international research team analyzed the beaches and found fragments of zircon that are much older, between 600 million and 2 billion years old.

Bjørn Jamtveit, a geologist at the University of Oslo explained that the zircons had crystallized within granites or other acidic igneous rocks (basalts being basic, non acidic). He believes that rocks containing these minerals came from a long-submerged landmass that was once wedged between India and Madagascar in a prehistoric supercontinent known as Rodinia; geologically recent volcanic eruptions brought the rocks up to the surface, where they were eroded, resulting in the shards they picked up. Most of the rocks were melted by the high temperatures, but some grains of zircons survived and were frozen into the lavas, rolling towards the Mauritian surface.

“When lavas moved through continental material on the way towards the surface, they picked up a few rocks containing zircon,” study co-author Bjørn Jamtveit, a geologist at the University of Oslo in Norway, explained in an email.

rodinia

The tectonic plates are mobile in geologic time – the surface of the Earth didn’t always look like this. As a matter of fact, the further down you go on the time scale, the more different it looks like. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago; virtually all of the Earth’s landmass was concentrated in this single supercontinent which started to split 3/4 billion years ago.

The study also analyzed the gravity field and as it turns out, something really interesting happened to the remains of Rodinia in that area. As India and Madagascar began to drift apart some 85 million years ago, the landmass just sinked, Atlantis style. The cause was tectonic rifting and sea-floor spreading sending the Indian subcontinent surging northeast, sinking the fragments of Mauritia (how the researchers named this microcontinent).

The variations in the gravitational field observed in some areas in Mauritius, the Seychelles, and the Maldives is pretty much a smoking gun suggesting a thick crust supporting the long-lost continent theory, with the continent being “tucked” under the Indian Ocean.

gravity

A non-geologic accident?

The only weak point, is that the study, thorough as it is, relies mostly on those zircons; couldn’t they be just some sort of non-geologic accident?

“There’s no obvious local source for these zircons,” says Conall Mac Niocaill, a geologist at the University of Oxford, UK, who was not involved in the research.

It also doesn’t look like they were brought there by winds.

“There’s a remote possibility that they were wind blown, but they’re probably too large to have done so,” adds Robert Duncan, a marine geologist at Oregon State University in Corvallis.

Also, the samples were picked up from remote sites, where it’s quite unlikely that humans would have brought them there. However, Jérôme Dyment, a geologist at the Paris Institute of Earth Physics in France, is not convinced. He believes that a number of non-geologic processes could have brought the minerals there, as part of ship ballast or modern construction material for example.

“Extraordinary claims require extraordinary evidence, which are not given by the authors so far,” said Dyment, who did not participate in the research. “Finding zircons in sand is one thing, finding them within a rock is another one … Finding the enclave of deep rocks that, according to the author’s inference, bring them to the surface during an eruption would be much more convincing evidence.”

He makes an even more convincing argument, explaining that if remains of such a continent were to exist, evidence for its existence should have been found as part of an ongoing experiment that installed deep-sea seismometers to investigate Earth’s mantle around Réunion Island, which is situated about 200 kilometers from Mauritius.

So is this compelling evidence, or is it more of an educated assertion? But Conall Mac Niocaill, a geologist at the University of Oxford in the U.K. who was also not involved in the study, is spot on: “the lines of evidence are, individually, only suggestive, but collectively they add up to a compelling story.”, he says. Particularly, the geophysic (gravimetric) evidence is highly consistent with the researchers’ claims. All in all, it paints a consistent picture which makes sense in a tectonic context, but as almost always in geology, you can’t just draw a line and say “This is so”; one thing’s for sure though: oceanic basins worldwide may very well host similarly submerged remains of “ghost continents”.

Via Nature Geoscience

Massive Indian Ocean quakes may signal tectonic break-up

The past few years have been marked by numerous seismic events, some of dramatic magnitude; aside from the huge 9.1 temblor in Japan, the world was also shocked by the pair of massive earthquakes that rocked the Indian Ocean on 11 April 2012. However, as geophysicists warn, this may only be the beginning – the birth of a new plate boundary.

A pair of massive earthquakes

Credits: Harvard University

The undersea earthquakes measured magnitudes of 8.6 and 8.2 and triggered tsunamis throughout the Indian Ocean. The damage was somewhat smaller than what you’d expect, but now, researchers claim their effects may be more far-reaching than first believed. Basically, the earthquakes were caused by accumulated geologic stress breaking the Indo-Australian plate apart; when they took place, they released energy across numerous faults and unleashed aftershocks for almost a week afterwards.

Ever since the 1980s, researchers believed the Indo-Australian plate is breaking apart, but until now, there hasn’t really been any conclusive evidence to support those claims. The April 11 earthquakes represents the most spectacular example of the process in action, as Matthias Delescluse, a geophysicist at the Ecole Normale Supérieure in Paris explains: “it’s the clearest example of newly formed plate boundaries,” he says.

Plate tectonics

According to generally accepted theories, the internal stressing and deformation of the Indo-Australian plate began some 10 million years ago; while the plate moved northwards, the Indian part was stopped by the Eurasian plate and dove under the Himalayas, rising them. However, the Australian part forged ahead, creating the tension which is breaking the plate apart today.

Gregory Beroza, a seismologist at Stanford University in Palo Alto, California, is also a believer in this model:

“The 2004 and 2005 earthquakes by themselves would not have caused this other earthquake. There had to be other stresses”, he says.

Earthquakes and strike-slips

Most earthquakes form at the boundary of tectonic plates, as you can see from the second picture above; one plate drifts beneath the other, creating massive earthquakes – this is called subduction. However, this is not the only form of contact between plates: plates or portions of plates can also slip by each other, horizontally, resulting in what is called as ‘strike-slip’ earthquakes. Typically, these earthquakes are smaller and less dangerous (though dangerous as well).

However, the first of the two earthquakes defied all expectations, being the largest strike slip earthquake on record, and one of the biggest to occur away from any plate boundaries.

Another study drew some pretty interesting, but worrying conclusion: the earthquake was created by accumulated stress throughout the plate, and the release of this stress created one of the most complex fault patterns in the world – something you really don’t want to hear if you live in that area. Typically, an earthquake like this shakes along a single fault, or maybe two if it’s a really big one; but this one shook no less than four faults, one of which slipped more than 20 meters. While this pattern has been described partially in previous work, nobody has analyzed slip amounts in so much detail: Beroza says that Lay and his team “do a splendid job of picking apart this very important earthquake” in their paper.

Aftershocks

So not only was this earthquake unique due to its high magnitude and slip, its aftershocks are also special. In yet another study, researchers found that for the six days following the temblor, aftershocks with magnitudes bigger than 5.5 occurred 5 times more often than normal.

“Aftershocks are usually restricted to the immediate vicinity of a main shock,” says lead author Fred Pollitz, a geophysicist at the US Geological Survey in Menlo Park, California.

However, this changes the general belief of how soon and how close aftershocks can occur after earthquakes, raising the importance of this particular earthquake even more.

“Every earthquake is important to study, but this earthquake is rather unique,” says Hiroo Kanamori, a seismologist at the California Institute of Technology in Pasadena.

Scientific sources: 1 2 3

A giant landslide on Iapetus reaches halfway across a 75-mile (120 kilometer) impact crater.(c) NASA/JPL/Space Science Institute

Giant landslides on Saturn’s icy moon intrigues scientists

A giant landslide on Iapetus reaches halfway across a 75-mile (120 kilometer) impact crater.(c) NASA/JPL/Space Science Institute

A giant landslide on Iapetus reaches halfway across a 75-mile (120 kilometer) impact crater.(c) NASA/JPL/Space Science Institute

Planetary scientist Kelsi Singer initially studied satellite photographs of  Saturn’s icy moon Iapetus‘ surface looking for stress fractures in the moon’s ice, what she found in process however was far more interesting. Huge landslides, stretching across tens of miles across the moon’s surface were observed, not in one, but multiple locations, hinting this is a common phenomenon on the ice covered satellite. Very broad landslides have been recorded on Earth as well, although nowhere near this magnitude, and the study at hand might serve to hint towards the mechanisms involved in these natural formations.

Iapetus is one of the oddest cosmic bodies in the solar system. Barren, cold and mostly covered in very thick ice, the satellite presents a highly rugged terrain, with ridges that can reach as much as 12 miles in height or two times the altitude of Mount Everest. Like the ubiquitous yin-yang, the moon’s surface is half covered in darkness, while the other side is much brighter. Moreover, it has the most eccentric geometry out of all the solar system’s planets or moons, made evident by a mountainous ridge that bulges out at its equator – this is why it’s commonly referred to as the “walnut”.

Iapentu's eccentric topography

Iapentu’s eccentric topography

Because of this incredibly odd topography, Iapetus  has more giant landslides than any Solar System body other than Mars. So far, evidence of 30 massive landslides have been found – 17 along crater walls and 13 along the giant equatorial ridge, however even more might be encountered if an exhaustive observation were to be performed.

“Not only is the moon out-of-round, but the giant impact basins are very deep, and there’s this great mountain ridge that’s 20km (12 miles) high, far higher than Mount Everest,” explained Prof William McKinnon, also from Washington University,.

“So there’s a lot of topography and it’s just sitting around, and then, from time to time, it gives way.”

The icy landslides are similar to long-runout landslides on Earth known as sturzstroms (German for fallstreams) – massive landslides can move up 20 to 30 times the height they fall from. Typically, on Earth, conventional landslides only travel around two times the height they fall from.

Apparently, the mechanism that governs the formation of these massive landslides, on Iapetus or here on Earth, has yet to reach an consensus from scientists. Various theories have been suggested from  riding on a cushion of trapped air, to sliding on groundwater or mud, to sliding on ice, or slipping caused by strong acoustic vibrations.

According to Singer, a graduate student in earth and planetary sciences at Washington University in St. Louis and lead author of the paper presently discussed, the massive landslides most likely  occur by frictional heating of the ice. Since it doesn’t have an atmosphere, the coefficient of friction – a measure of how much the slip-sliding of material in a landslide tends to slow it down – on Iapetus is far lower than expected for ice.

Despite the ice on Iapetus is as a solid as rock, scientists hypothesize that  tiny contact points between bits of ice debris in such a landslide may heat up considerably,leading to a thin layer of ice crystals that melts. This might cause the huge landslides on Saturn’s icy moon, but could also serve to explain how sturzstroms form on Earth.

“The landslides on Iapetus are a planet-scale experiment that we cannot do in a laboratory or observe on Earth,” Ms Singer said.

“They give us examples of giant landslides in ice, instead of rock, with a different gravity, and no atmosphere. So any theory of long-runout landslides on Earth must also work for avalanches on Iapetus.”

The findings were reported in the journal  Nature Geoscience