Mechanism of Slow Earthquakes Reproduce

catching lightning in a bottle has been easier than reproducing a range of earthquakes in the laboratory, according to a team of seismologists who can now duplicate the range of fault slop modes found during earthquakes, quiet periods and slow earthquakes.

Catastrophic earthquakes, the kind that destroy buildings and send people scurrying for doorways and safe locations are caused when two tectonic plates that are sliding in opposite directions stick and then slop suddenly, releasing a large amount of energy, creating tremors and sometimes causing destruction. Along regions of faults that do not produce earthquakes, the two sides of the fault slowly slip past each other in a stable fashion. Slow earthquakes occur somewhere between the stable regime and fast stick slip.

Regular earthquakes take place rapidly, while slow slow earthquakes occur on time scales that may range up to  months. They can be as large as magnitude 7or more and may be precursors to regular earthquakes. However, slow earthquakes propagate slowly and do not produce high-frequency seismic energy. They exist in the regime between stable slipping and regular earthquakes.

The researchers applied stress perpendicular to the direction of shear and then applied forces to shear the ground quartz. By altering the amount of stress placed in the perpendicular direction,they could achieve the audible crack of a regular earthquake, stable slippage and a wide range of slip-stick behaviors including slow earthquake.

Earthquake at Jalpaiguri

According to the Mousum Bhaban of Delhi, an earthquake hits the North Bengal on Saturday night around 9:45.
According to the report the center of the quake is 21 km under the earth surface of the Jalpaiguri district. The magnitude of the earthquake is 3.8..
According to the locals those who lived in the multi-storied building could feel the ground shaking, within minutes, panic spread across the area and people came out of their  houses.
The jolts comes 11 months after the Nepal quake that felt the country in shock.

Explosive volcanoes fueled by water

Geologists have tapped water in surface rocks to show how magma forms deep underground and produces explosive volcanoes in the Cascade Range. 

"Water is a key player," says Paul J. Wallace, a professor in the UO's Department of Geological Sciences and coauthor of a paper in the May issue of Nature Geoscience. "It's important not just for understanding how you make magma and volcanoes, but also because the big volcanoes that we have in the Cascades -- like Mount Lassen and Mount St. Helens -- tend to erupt explosively, in part because they have lots of water."

A five-member team, led by UO doctoral student Kristina J. Walowski, methodically examined water and other elements contained in olivine-rich basalt samples that were gathered from cinder cone volcanoes that surround Lassen Peak in Northern California, at the southern edge of the Cascade chain.

The discovery helps solve a puzzle about plate tectonics and Earth's deep water cycle beneath the Pacific Ring of Fire, which scientists began studying in the 1960s to understand the region's propensity for big earthquakes and explosive volcanoes. The ring stretches from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska and south along the coast of North and South America. It contains more than 75 percent of the planet's volcanoes.

To understand how water affects subduction of the oceanic plate, in which layers of different rock types sink into the mantle, the UO team studied hydrogen isotopes in water contained in tiny blobs of glass trapped in olivine crystals in basalt.

To do so, the team used equipment in Wallace's lab, CAMCOR, the Carnegie Institution in Washington, D.C., and a lab at Oregon State University. CAMCOR is UO's Advanced Materials Characterization in Oregon, a high-tech extension service located in the underground Lorry I. Lokey Laboratories.

Next, the team fed data gained from the rocks into a complex computer model developed by co-author Ikudo Wada, then of Japan's Tohoku University. She has since joined the University of Minnesota.

That combination opened a window on how rising temperatures during subduction drive water out of different parts of the subducted oceanic crust, Walowski said. Water migrates upwards and causes the top of the subducted oceanic crust to melt, producing magma beneath the Cascade volcanoes.

The key part of the study, Wallace said, involved hydrogen isotopes. "Most of the hydrogen in water contains a single proton," he said. "But there's also a heavy isotope, deuterium, which has a neutron in addition to the proton. It is important to measure the ratio of the two isotopes. We use this ratio as a thermometer, or probe, to study what's happening deep inside the earth."

"Melting of the subducting oceanic crust and the mantle rock above it would not be possible without the addition of water," Walowski said. "Once the melts reach the surface, the water can directly affect the explosiveness of magma. However, evidence for this information is lost to the atmosphere during violent eruptions."

This story is taken from Science Daily

Did dinosaur-killing asteroid trigger largest lava flows on Earth?

The theory that an asteroid impact killed off the dinosaurs 66 million years ago is well accepted, but one puzzle is why another global catastrophe -- the huge, million-year eruption of the Deccan Traps flood basalts in India -- occurred at the same time. Geologists now argue this is not a coincidence. The impact probably rang Earth like a bell, reigniting an underground magma plume and generating the largest lava flows on Earth. 

Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India known as the Deccan Traps, explaining the "uncomfortably close" coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.

"If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan ... the chances of that occurring at random are minuscule," said team leader Mark Richards, UC Berkeley professor of earth and planetary science. "It's not a very credible coincidence."

Richards and his colleagues marshal evidence for their theory that the impact reignited the Deccan flood lavas in a paper to be published in The Geological Society of America Bulletin, available online today (April 30) in advance of publication.

While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after re-ignition, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it's still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs, Richards said.

"This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn't yet take us closer to understanding what actually killed the dinosaurs and the 'forams,'" he said, referring to tiny sea creatures called foraminifera, many of which disappeared from the fossil record virtually overnight at the boundary between the Cretaceous and Tertiary periods, called the KT boundary. The disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.

He stresses that his proposal differs from an earlier hypothesis that the energy of the impact was focused around Earth to a spot directly opposite, or antipodal, to the impact, triggering the eruption of the Deccan Traps. The "antipodal focusing" theory died when the impact crater, called Chicxulub, was found off the Yucatán coast of Mexico, which is about 5,000 kilometers from the antipode of the Deccan traps.

Flood basalts

Richards proposed in 1989 that plumes of hot rock, called "plume heads," rise through Earth's mantle every 20-30 million years and generate huge lava flows, called flood basalts, like the Deccan Traps. It struck him as more than coincidence that the last four of the six known mass extinctions of life occurred at the same time as one of these massive eruptions.

"Paul Renne's group at Berkeley showed years ago that the Central Atlantic Magmatic Province is associated with the mass extinction at the Triassic/Jurassic boundary 200 million years ago, and the Siberian Traps are associated with the end Permian extinction 250 million years ago, and now we also know that a big volcanic eruption in China called the Emeishan Traps is associated with the end-Guadalupian extinction 260 million years ago," Richards said. "Then you have the Deccan eruptions -- including the largest mapped lava flows on Earth -- occurring 66 million years ago coincident with the KT mass extinction. So what really happened at the KT boundary?"

Richards teamed up with experts in many areas to try to discover faults with his radical idea that the impact triggered the Deccan eruptions, but instead came up with supporting evidence. Renne, a professor in residence in the UC Berkeley Department of Earth and Planetary Science and director of the Berkeley Geochronology Center, re-dated the asteroid impact and mass extinction two years ago and found them essentially simultaneous, but also within approximately 100,000 years of the largest Deccan eruptions, referred to as the Wai subgroup flows, which produced about 70 percent of the lavas that now stretch across the Indian subcontinent from Mumbai to Kolkata.

Michael Manga, a professor in the same department, has shown over the past decade that large earthquakes -- equivalent to Japan's 9.0 Tohoku quake in 2011 -- can trigger nearby volcanic eruptions. Richards calculates that the asteroid that created the Chicxulub crater might have generated the equivalent of a magnitude 9 or larger earthquake everywhere on Earth, sufficient to ignite the Deccan flood basalts and perhaps eruptions many places around the globe, including at mid-ocean ridges.

"It's inconceivable that the impact could have melted a whole lot of rock away from the impact site itself, but if you had a system that already had magma and you gave it a little extra kick, it could produce a big eruption," Manga said.

Similarly, Deccan lava from before the impact is chemically different from that after the impact, indicating a faster rise to the surface after the impact, while the pattern of dikes from which the supercharged lava flowed -- "like cracks in a soufflé," Renne said -- are more randomly oriented post-impact.

"There is a profound break in the style of eruptions and the volume and composition of the eruptions," said Renne. "The whole question is, 'Is that discontinuity synchronous with the impact?'"

Reawakened volcanism

Richards, Renne and graduate student Courtney Sprain, along with Deccan volcanology experts Steven Self and Loÿc Vanderkluysen, visited India in April 2014 to obtain lava samples for dating, and noticed that there are pronounced weathering surfaces, or terraces, marking the onset of the huge Wai subgroup flows. Geological evidence suggests that these terraces may signal a period of quiescence in Deccan volcanism prior to the Chicxulub impact. Apparently never before noticed, these terraces are part of the western Ghats, a mountain chain named after the Hindu word for steps.

"This was an existing massive volcanic system that had been there probably several million years, and the impact gave this thing a shake and it mobilized a huge amount of magma over a short amount of time," Richards said. "The beauty of this theory is that it is very testable, because it predicts that you should have the impact and the beginning of the extinction, and within 100,000 years or so you should have these massive eruptions coming out, which is about how long it might take for the magma to reach the surface."

This story is taken from Science Daily

Rupture along the Himalayan Front

In an article in March, geologists noted that the 700-km-long 'central seismic gap' is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200-500 years. This prolonged seismic quiescence has led to the proposition that this region, with a population of more 10 million, is overdue for a great earthquake.' 

A little more than a month on, the area experienced a magnitude 7.8 earthquake, centered in Nepal (25 Apr. 2015).
In their study, Morell and colleagues use a series of complementary geomorphic and erosion rate data to define the ramp-flat geometry of the active detachment fault that is likely to host a large earthquake within the hinterland of the northwest Himalaya. Their analysis indicates that this detachment is sufficiently large to host another great earthquake in the western half of the central Himalayan seismic gap.
Specifically, their data sets point to a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates.
When combined with previously published geophysical imaging and seismicity data sets, Morell and colleagues interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. They write, "Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake."
In conclusion, they note, "While this hypothesis remains speculative, it is supported by independent records of historical seismicity."

This story is taken from Science Daily

Landslides, mudslides likely to remain a significant threat in Nepal for months

The threat of landslides and mudslides remains high across much of Nepal's high country, and the risk is likely to increase when the monsoon rains arrive this summer, according to a researcher. 

U-M geomorphologist Marin Clark and two colleagues have assessed the landslide hazard in Nepal following Saturday's magnitude-7.8 earthquake. They looked for locations where landslides likely occurred during the earthquake, as well as places that are at high risk in the coming weeks and months.
The analysis revealed tens of thousands of locations at high risk, Clark said.
"The majority of them, we expect, have already happened and came down all at once with the shaking on Saturday," she said. "But there will still be slopes that have not yet failed but were weakened. So there will be a continued risk during aftershocks and with the recent rainfall, and again when the monsoon rains arrive this summer."
Information from the U-M-led study has been shared with the U.S Geological Survey, NASA, the U.S. Agency for International Development and other responding agencies. It is being used help prioritize both satellite observations and the analysis of data from those satellites, said Clark, an associate professor in the U-M Department of Earth and Environmental Sciences.
"The satellites looked first at places where lots of people live, including Kathmandu and the foothills areas to the south," Clark said. "Those areas do not look significantly impacted by landsliding, but we're worried about the high country," she said.
The region at highest risk for landslides and mudslides is the mountainous area along the Nepal-Tibet border, north of Kathmandu and west of Mount Everest, directly above the fault rupture. The highest-risk zone is at elevations above 8,200 feet in a region that covers 17,550 square miles, which is roughly twice the size of Massachusetts.
Cloud cover has blocked observation of much of that region since Saturday's earthquake. But news stories and social media reports of landslides in Nepal's Gorka District and Langtang Valley are consistent with the Clark team's assessment, which showed that those areas are at high risk, she said.
Remote villages are scattered throughout the high-risk zone, which also contains the main highway that connects Kathmandu and Tibet. The area is popular with trekkers and mountaineers, as well.
"Many small Nepalese villages throughout this region have likely been cut off from the rescue operation," Clark said. "This is also high season for trekking and mountaineering, so I expect there are a large number of foreign tourists there, as well."
The Clark team's assessment of the landslide risk was based on a computer analysis that looked at earthquake shaking, slope steepness and the strength of various rock types.
Their initial analysis was completed Saturday afternoon and was shared with the U.S. Geological Survey and other agencies on Saturday evening. It was revised Sunday morning and distributed through the National Earthquake Hazards Reduction Program on Sunday afternoon.
More than 200,000 landslides occurred following a magnitude-7.9 earthquake in a mountainous region of Sichuan Province, China, in 2008, according to Clark. Many of those landslides blocked roads, which slowed response and recovery efforts. The final death toll for that quake was about 70,000.
Landsliding is a general term for slowly to very rapidly descending rock and debris. A mudslide or mudflow is a fluid mix of mud and debris that moves down a slope.
Landslides in mountainous regions can also block river valleys, creating a significant flooding hazard. Water builds up behind those dam-like structures, creating the potential for catastrophic flooding if the dams are overtopped and then fail.
"With the satellite images, we'll be looking first at the highest-risk landslide areas that are close to big rivers," Clark said. "Those locations are high priorities."
Clark's collaborators on the landslide hazard assessment are U-M's Nathan Niemi and Sean Gallen, a former U-M postdoctoral researcher under Clark who recently accepted a position at ETH Zurich in Switzerland.

This story is taken from Science Daily

Tidal tugs on 'Teflon' faults drive slow-slipping earthquakes

Teasing out how slow, silent earthquakes respond to tidal forces lets researchers calculate the friction inside the fault, which could help understand when and how the more hazardous earthquakes occur. 

A University of Washington seismologist who studies slow-slip quakes has looked at how they respond to tidal forces from celestial bodies and used the result to make a first direct calculation of friction deep on the fault. Though these events occur much deeper and on a different type of fault than the recent catastrophe in Nepal, the findings could improve general understanding of when and how faults break.

The new study, published online April 27 in Nature Geoscience, shows that the gravitational pull of the sun and the moon affect the Cascadia fault a few days after it has started slipping. The timing of movement suggests that the friction at this depth on the fault is only 0.1, roughly that of two pieces of lubricated metal.

"I was able to tease out the effect of friction and found that it is not the friction of normal rocks in the lab -- it's much lower," said author Heidi Houston, a UW professor of Earth and space sciences. "It's closer to Teflon than to sandpaper."

The surprising results of the new study could help to better model the physics of these systems, and they could even tell us something about the frictional forces in the locked portion of the fault where hazardous earthquakes occur.

The research looked at six recent slow-slip events along the Cascadia subduction zone, one of the best-studied places for these enigmatic slow quakes. The slow quakes are accompanied by tremors, weak seismic vibrations previously thought to be random noise. The tremors begin every 12 to 14 months below Puget Sound, Washington, and then travel north and south at about 5 miles (8 kilometers) per day for several weeks, affecting each section of the fault for about five days.

The paper looks at how the gravitational pull of the sun and moon, which slightly deform Earth and oceans, affect forces along, across and inside the fault, and what that means for the slow-slip seismic activity more than 20 miles (35 kilometers) underground.

Results show that on the first day of tremors, the tidal forces don't matter much. But starting at about 1 1/2 days -- when Houston thinks minerals that had been deposited from the surrounding fluid and that held the fault together may have broken -- the additional pull of the tides does have an effect.

"Three days after the slipping has begun, the fault is very sensitive to the tides, and it almost slips only when the tides are encouraging it," Houston said.

"It implies that something is changing on the fault plane over those five days."

By averaging across many sections of the fault, and over all six events, she found that the amount of the tremor increases exponentially with increasing tidal force.

Regular fast earthquakes are also very slightly affected by the tides, but they are overwhelmed by other forces and the effect is almost too small to detect.

There is no need for worry, Houston says -- even when celestial bodies line up to generate the biggest king tides, the effect would only rarely be enough to actually trigger a slow-slip quake, much less a regular earthquake. But it does tell us something about the physics of a crucial process that can't be easily studied in the lab.

"We want to understand the physics of what is happening, to understand and predict how the fault is storing stress, and how it's going to relieve stress," Houston said. "Friction is a big piece of that. And it turns out that this part of the fault is much slipperier than previously thought."

Slow-slip earthquakes relieve stress right where they slipped, but the movement actually places more stress on neighboring parts of the fault, including the so-called locked zone, where a rupture can cause the most damaging type of earthquakes.

In Cascadia's slow-slip events the fault will move about an inch (3 centimeters) over several days, with different parts of the fault moving at different times. When the shallower "locked zone" ruptures, by contrast, a large section of the fault can lurch over 60 feet (18 meters) in minutes. When this occurs, as it does about every 500 years in a magnitude 9 on the Cascadia subduction zone, it generates strong damaging seismic waves in Earth's crust.

Still unknown is how slow-slip events are related to the more damaging quakes. A shallower slow-slip event was detected in the weeks before the deadly 2011 Tohoku earthquake and tsunami, on a fault like Cascadia's where an ocean plate plunges below a continental plate.

"Understanding slow slip and tremor could give us some way to monitor what is happening in the shallower, locked part of the fault," Houston said. "Geophysicists started with the picture of just a flat plane of sandpaper, but that picture is evolving."

This story is taken from Science Daily

Signs of ancient earthquakes may raise risks for New Zealand

Researchers have uncovered the first geologic evidence that New Zealand's southern Hikurangi margin can rupture during large earthquakes. The two earthquakes took place within the last 1000 years, and one was accompanied by a tsunami, according to the study. 

The earthquakes took place roughly 350 years apart, according to the analysis by Kate Clark of GNS Science and colleagues. This may mean that the time between large earthquakes in this region is shorter than scientists have thought. The current seismic models account for these types of earthquakes every 500 to 1000 years.
A worst-case, M8.9 Hikurangi earthquake could cause about 3350 deaths and 7000 injuries, and lead to $13 billion in costs in New Zealand's capital Wellington alone, according to a calculation made in 2013 by a different set of scientists. The Hikurangi margin marks the area where the Pacific and Australian tectonic plates collide to the east of New Zealand. The margin is one of the few places around the Pacific where a major subduction interface earthquake--which occurs deep in the crust where one plate is thrust under another--has not occurred in historic times.
However, "subduction earthquakes are not a 'new' risk for New Zealand, as we have always assumed they can occur, and they are accounted for in our seismic hazard models," Clark said. "This study is significant in that it confirms that risk.
"We have a record of three to five past earthquakes on most of the major upper plate faults in the [New Zealand] lower North Island and upper South Island, but there was previously no evidence of past subduction earthquakes on the southern Hikurangi margin," Clark explained. "Subduction earthquakes have the potential to be significantly larger in magnitude than upper plate fault ruptures, affect a much larger spatial area and are much more likely to trigger tsunami."
To look for evidence of past earthquakes on the margin, the researchers performed a painstaking examination of the geologic layers contained within a salt marsh at Big Lagoon in the southeastern Wairau River valley on South Island. They analyzed cores drilled from the marsh to look at differences in the kinds of sediment and the shells from tiny marine animals called foraminifera, deposited throughout a stretch of the lagoon's history.
These data revealed that the lagoon sank relatively suddenly twice during the past 1000 years, suggesting that the land was subsiding as a result of significant earthquakes. The more recent earthquake occurred between 520 and 470 years ago.
Another earlier earthquake probably took place between 880 and 800 years ago. Judging by the sedimentary debris found at that time, this earthquake was accompanied by a tsunami that swept more than 360 meters inland at the study site.
Clark said the findings will help researchers better understand the risks posed by large subduction interface earthquakes in the region. Studies have shown, for example, that there have been subduction earthquakes on the central Hikurangi margin, "and we wanted to understand if the central and southern Hikurangi margins are likely to rupture in the same earthquake," said Clark.
"We can see that the [southern Hikurangi margin] subduction earthquake at about 500 years before present possibly correlates with a central Hikurangi margin earthquake, implying both segments may have ruptured in the same earthquake," she continued, "but the radiocarbon dating is not yet precise enough to be certain--possibly there were two earthquake closely spaced in time."
Clark said that she and other scientists are looking at other locations in the lower North Island to find evidence of the same paleoearthquakes, which could help provide a better picture of how big these quakes might have been and how they impacted the region.
"In addition we would like to go further back in time and find evidence of older subduction earthquakes," Clark said."With a longer record of past subduction earthquakes we can get a better constraint on the recurrence of such earthquakes, which will help to forecast future subduction earthquakes."

This story is taken from Science Daily

Seafloor sensors record possible eruption of underwater volcano

If a volcano erupts at the bottom of the sea, does anybody see it? If that volcano is Axial Seamount, about 300 miles offshore and 1 mile deep, the answer is now: yes. 

Thanks to a set of high-tech instruments installed last summer by the University of Washington to bring the deep sea online, what appears to be an eruption of Axial Volcano on April 23 was observed in real time by scientists on shore.

"It was an astonishing experience to see the changes taking place 300 miles away with no one anywhere nearby, and the data flowed back to land at the speed of light through the fiber-optic cable connected to Pacific City -- and from there, to here on campus by the Internet, in milliseconds," said John Delaney, a UW professor of oceanography who led the installation of the instruments as part of a larger effort sponsored by the National Science Foundation.

This custom-built precise pressure sensor detects the seafloor's rise and fall as magma, or molten rock, moves in and out of the underlying magma chamber. Three are installed on the caldera of the underwater volcano.NSF-OOI/UW/CSSF

Delaney organized a workshop on campus in mid-April at which marine scientists discussed how this high-tech observatory would support their science. Then, just before midnight on April 23 until about noon the next day, the seismic activity went off the charts.

The gradually increasing rumblings of the mountain were documented over recent weeks by William Wilcock, a UW marine geophysicist who studies such systems.

During last week's event, the earthquakes increased from hundreds per day to thousands per day, and the center of the volcanic crater dropped by about 6 feet (2 meters) over the course of 12 hours.

"The only way that could have happened was to have the magma move from beneath the caldera to some other location," Delaney said, "which the earthquakes indicate is right along the edge of the caldera on the east side."

The seismic activity was recorded by eight seismometers that measure shaking up to 200 times per second around the caldera and at the base of the 3,000-foot seamount. The height of the caldera was tracked by the bottom pressure tilt instrument, which measures the pressure of the water overhead and then removes the effect of tides and waves to calculate its position.

The depth instrument was developed by Bill Chadwick, an oceanographer at Oregon State University and the National Oceanic and Atmospheric Administration who has also been tracking the activity at Axial Volcano and predicted that the volcano would erupt in 2015.

The most recent eruptions were in 1998 and 2011.

The volcano is located about 300 miles west of Astoria, Oregon, on the Juan de Fuca Ridge, part of the globe-girdling mid-ocean ridge system -- a continuous, 70,000 km (43,500 miles) long submarine volcanic mountain range stretching around the world like the strings on a baseball, and where about 70 percent of the planet's volcanic activity occurs. The highly energetic Axial Seamount, Delaney said, is viewed by many scientists as being representative of the myriad processes operating continuously along the powerful subsea volcanic chain that is present in every ocean.

"This exciting sequence of events documented by the OOI-Cabled Array at Axial Seamount gives us an entirely new view of how our planet works," said Richard Murray, division director for ocean sciences at the National Science Foundation. "Although the OOI-Cabled Array is not yet fully operational, even with these preliminary observations we can see how the power of innovative instrumentation has the potential to teach us new things about volcanism, earthquakes and other vitally important scientific phenomena."

The full set of instruments in the deep-sea observatory is scheduled to come online this year. A first maintenance cruise leaves from the UW in early July, and will let researchers and students further explore the aftermath of the volcanic activity.

This story is taken from Science Daily

Earthquakes reveal deep secrets beneath East Asia

A new supercomputer model combined earthquake data to create 3-D tomographic images to depths of 900 km, or 560 miles below East Asia. Notable features found include a high velocity structure beneath Tibetan Plateau; and a deep mantle upwelling under Hangai dome in Mongolia.This research could help find hidden hydrocarbon resources and explore deep structures elsewhere. 

The scientists used seismic data from 227 East Asia earthquakes during 2007-2011, which they used to image depths to about 900 kilometers, or about 560 miles below ground.
Notable structures include a high velocity colossus beneath the Tibetan plateau, and a deep mantle upwelling beneath the Hangai Dome in Mongolia. The researchers say their line of work could potentially help find hidden hydrocarbon resources, and more broadly it could help explore the Earth under East Asia and the rest of the world.
"With the help of supercomputing, it becomes possible to render crystal-clear images of Earth's complex interior," principal investigator and lead author Min Chen said of the study. Chen is a postdoctoral research associate in the department of Earth Sciences at Rice University.
Chen and her colleagues ran simulations on the Stampede and Lonestar4 supercomputers of the Texas Advanced Computing Center through an allocation by XSEDE, the eXtreme Science and Engineering Discovery Environment funded by the National Science Foundation.
"We are combining different kinds of seismic waves to render a more coherent image of the Earth," Chen said. "This process has been helped by supercomputing power that is provided by XSEDE."
"What is really new here is that this is an application of what is sometimes referred to as full waveform inversion in exploration geophysics," study co-author Jeroen Tromp said. Tromp is a professor of Geosciences and Applied and Computational Mathematics, and the Blair Professor of Geology at Princeton University.
In essence the application combined seismic records from thousands of stations for each earthquake to produce scientifically accurate, high-res 3-D tomographic images of the subsurface beneath immense geological formations.
XSEDE provided more than just time on supercomputers for the science team. Through the Campus Champions program, researchers worked directly with Rice XSEDE champion Qiyou Jiang of Rice's Center for Research Computing and with former Rice staffer Roger Moye, who used Rice's DAVinCI supercomputer to help Chen with different issues she had with high performance computing." "They are the contacts I had with XSEDE," Chen said.
"These collaborations are really important," said Tromp of XSEDE. "They cannot be done without the help and advice of the computational science experts at these supercomputing centers. Without access to these computational resources, we would not be able to do this kind of work."
Like a thrown pebble generates ripples in a pond, earthquakes make waves that can travel thousands of miles through the Earth. A seismic wave slows down or speeds up a small percentage as it travels through changes in rock composition and temperature. The scientists mapped these wave speed changes to model the physical properties of rock hidden below ground.
Tromp explained that the goal for his team was to match the observed ground-shaking information at seismographic stations to fully numerical simulations run on supercomputers.
"In the computer, we set off these earthquakes," says Tromp. "The waves ripple across southeast Asia. We simulate what the ground motion should look like at these stations. Then we compare that to the actual observations.
The differences between our simulations and the observations are used to improve our models of the Earth's interior," Tromp said. "What's astonishing is how well those images correlate with what we know about the tectonics, in this case, of East Asia from surface observations."
The Tibetan Plateau, known as 'the roof of the world,' rises about three miles, or five kilometers above sea level. The details of how it formed remain hidden to scientists today.
The leading theory holds that the plateau formed and is maintained by the northward motion of the India plate, which forces the plateau to shorten horizontally and move upward simultaneously.
Scientists can't yet totally account for the speed of the movement of ground below the surface at the Tibetan Plateau or what happened to the Tethys Ocean that once separated the India and Eurasia plates. But a piece of the puzzle might have been found.
"We found that beneath the Tibetan plateau, the world's largest and highest plateau, there is a sub-vertical high velocity structure that extends down to the bottom of the mantle transition zone," Chen said.
The bottom of the transition zone goes to depths of 660 kilometers, she said. "Three-dimensional geometry of the high velocity structure depicts the lithosphere beneath the plateau, which gives clues of the fate of the subducted oceanic and the continental parts of the Indian plate under the Eurasian plate," Chen said.
The collision of plates at the Tibetan Plateau has caused devastating earthquakes, such as the recent 2015 Nepal earthquake at the southern edge of where the two plates meet. Scientists hope to use earthquakes to model the substructure and better understand the origins of these earthquakes.
To reach any kind of understanding, the scientists first grappled with some big data, 1.7 million frequency-dependent traveltime measurements from seismic waveforms. "We applied this very sophisticated imaging technique called adjoint tomography with a key component that is a numerical code package called SPECFEM3D_GLOBE," Chen said.
Specifically, they used SPECFEM3D GLOBE, open source software maintained by the UC Davis Computational Infrastructure for Geodynamics. "It uses parallel computing to simulate the very complex seismic waves through the Earth," Chen said.
Even with the tools in place, the study was still costly. "The cost is in the simulations of the wave propagation," says Tromp. "That takes hundreds of cores for tens of minutes at a time per earthquake.
As you can imagine, that's a very expensive proposition just for one iteration simulating all these 227 earthquakes." In all, the study used about eight million CPU hours on the Stampede and Lonestar4 supercomputers.
"The big computing power of supercomputers really helped a lot in terms of shortening the simulation time and in getting an image of the Earth within a reasonable timeframe," said Chen. "It's still very challenging. It took us two years to develop this current model beneath East Asia. Hopefully, in the future it's going to be even faster."
Three-D imaging inside the Earth can help society find new resources, said Tromp. The iterative inversion methods they used to model structures deep below are the same ones used in exploration seismology to look for hidden hydrocarbons.
"There's a wonderful synergy at the moment," Tromp said. "The kinds of things we're doing here with earthquakes to try and image the Earth's crust and upper mantle and what people are doing in exploration geophysics to try and image hydrocarbon reservoirs."
"In my point of view, it's the era of big seismic data," Chen said. She said their ultimate goal is to make everything about seismic imaging methods automatic and accessible by anyone to better understand the Earth.
It sounded something like a Google Earth for inside the Earth itself. "Right, exactly. Assisted by the supercomputing systems of XSEDE, you can have a tour inside the Earth and possibly make some new discoveries." Chen said.

This story is taken from Science Daily

Common mechanism for shallow and deep earthquakes proposed

Geologists report that a universal sliding mechanism operates for earthquakes of all depths -- from the deep ones all the way up to the crustal ones. The physics of the sliding is the self-lubrication of the earthquake fault by flow of a new material consisting of tiny new crystals, the study reports. 

A new study published online in Nature Geoscience today by a research team led by University of California, Riverside geologists now reports that a universal sliding mechanism operates for earthquakes of all depths -- from the deep ones all the way up to the crustal ones.
"Although shallow earthquakes -- the kind that threaten California -- must initiate differently from the very deep ones, our new work shows that, once started, they both slide by the same physics," said deep-earthquake expert Harry W. Green II, a distinguished professor of the Graduate Division in UC Riverside's Department of Earth Sciences, who led the research project. "Our research paper presents a new, unifying model of how earthquakes work. Our results provide a more accurate understanding of what happens during earthquake sliding that can lead to better computer models and could lead to better predictions of seismic shaking danger."
The physics of the sliding is the self-lubrication of the earthquake fault by flow of a new material consisting of tiny new crystals, the study reports. Both shallow earthquakes and deep ones involve phase transformations of rocks that produce tiny crystals of new phases on which sliding occurs.
"Other researchers have suggested that fluids are present in the fault zones or generated there," Green said. "Our study shows fluids are not necessary for fault weakening. As earthquakes get started, local extreme heating takes place in the fault zone. The result of that heating in shallow earthquakes is to initiate reactions like the ones that take place in deep earthquakes so they both end up lubricated in the same way."
Green explained that at 300-700 kilometers depth, the pressure and temperature are so high that rocks in this deep interior of the planet cannot break by the brittle processes seen on Earth's surface. In the case of shallow earthquakes, stresses on the fault increase slowly in response to slow movement of tectonic plates, with sliding beginning when these stresses exceed static friction. While deep earthquakes also get started in response to increasing stresses, the rocks there flow rather than break, except under special conditions.
"Those special conditions of temperature and pressure induce minerals in the rock to break down to other minerals, and in the process of this phase transformation a fault can form and suddenly move, radiating the shaking -- just like at shallow depths," Green said.
The research explains why large faults like the San Andreas Fault in California do not have a heat-flow anomaly around them. Were shallow earthquakes to slide by the grinding and crunching of rock, as geologists once imagined, the process would generate enough heat so that major faults like the San Andreas would be a little warmer along their length than they would be otherwise.
"But such a predicted warm region along such faults has never been found," Green said. "The logical conclusion is that the fault must move more easily than we thought. Extreme heating in a very thin zone along the fault produces the very weak lubricant. The volume of material that is heated is very small and survives for a very short time -- seconds, perhaps -- followed by very little heat generation during sliding because the lubricant is very weak."
The new research also explains why faults with glass on them (reflecting the fact that during the earthquake the fault zone melted) are rare. As shallow earthquakes start, the temperature rises locally until it is hot enough to start a chemical reaction -- usually the breakdown of clays or carbonates or other hydrous phases in the fault zone. The reactions that break down the clays or carbonates stop the temperature from climbing higher, with heat being used up in the reactions that produce the nanocrystalline lubricant.
If the fault zone does not have hydrous phases or carbonates, the sudden heating that begins when sliding starts raises the local temperature on the fault all the way to the melting temperature of the rock. In such cases, the melt behaves like a lubricant and the sliding surface ends up covered with melt (that would quench to a glass) instead of the nanocrystalline lubricant.
"The reason this does not happen often, that is, the reason we do not see lots of faults with glass on them, is that the Earth's crust is made up to a large degree of hydrous and carbonate phases, and even the rocks that don't have such phases usually have feldspars that get crushed up in the fault zone," Green explained. "The feldspars will 'rot' to clays during the hundred years or so between earthquakes as water moves along the fault zone. In that case, when the next earthquake comes, the fault zone is ready with clays and other phases that can break down, and the process repeats itself."
The research involved the study of laboratory earthquakes -- high-pressure earthquakes as well as high-speed ones -- using electron microscopy in friction and faulting experiments. It was Green's laboratory that first conducted a serendipitous series of experiments, in 1989, on the right kind of mantle rocks that give geologists insight into how deep earthquakes work. In the new work, Green and his team also investigated the Punchbowl Fault, an ancestral branch of the San Andreas Fault that has been exhumed by erosion from several kilometers depth, and found nanometric materials within the fault -- as predicted by their model.

This story is taken from Science Daily