The hydrothermal circulation changes the ocean crust and increases the Chlorine (CL) concentration of the rocks by incorporation of sea water. The magma takes up parts of this crust leading to an increase of chlorine of the magma. If the magma erupts at the sea floor, basalt lava is formed that we sampled and investigated in detail. Credit: GEOMAR
How deep can seawater penetrate through cracks and fissures into the seafloor? By applying a new analysis method, an international team of researchers has now discovered that the water can penetrate to depths of more than 10 kilometers below the seafloor. This result suggests a stronger cooling effect on the hot mantle.
Hot vents in the deep sea and geysers on land document the penetration of water into the hot interior of the Earth. This happens primarily in regions where the crust breaks up and magma chambers are close to the surface, e.g. in the area of mid-ocean ridges. But how deep does the water penetrate and cool the upper part of the hot mantle? So far it has been assumed that this process only reaches depths of a few kilometres. A new analytical method, developed at GEOMAR Helmholtz Centre for Ocean Research Kiel, now shows that water penetrates much deeper into the Earth than previously thought.
“Chlorine is the key element in our investigations,” explains Dr. Froukje van der Zwan, first author of the GEOMAR study. “We were able to detect this indicator for seawater in basalt rock even in very low concentrations,” van der Zwan continues. In her PhD thesis, she developed a new method to study chlorine levels in rock samples collected at the Southern Mid-Atlantic Ridge and Gakkel Ridge in Central Arctic. In addition, a chemical analysis of selected crystals in the rocks samples also allowed the depth at which the chlorine was incorporated into the rock to be determined.
“For our analyses, we had to push the electron-beam microprobe to its limits. It is a special scanning electron microscope, to which spectrometers are attached for the quantitative analysis of major, minor and trace element concentration,” van der Zwan explains. The microprobe, as well as other necessary devices, were available at GEOMAR. Furthermore, with the results of this study, the authors were able to verify theoretical models that were developed at GEOMAR.
“So far, it has been assumed that high pressure and temperatures prevented water from penetrating below 10 kilometres,” says Prof. Dr. Colin Devey, co-author of the GEOMAR study. “We can now show that the water penetrates much deeper,” Devey continues. This finding is important for the cooling of the oceanic crust and its heat budget, as well as for the total level of volatiles in the oceanic crust, which are later subducted and recycled into the mantle.
Reference:
Froukje M. van der Zwan, Colin W. Devey, Thor H. Hansteen, Renat R. Almeev, Nico Augustin, Matthias Frische, Karsten M. Haase, Ali Basaham, Jonathan E. Snow. Lower crustal hydrothermal circulation at slow-spreading ridges: evidence from chlorine in Arctic and South Atlantic basalt glasses and melt inclusions. Contributions to Mineralogy and Petrology, 2017; 172 (11-12) DOI: 10.1007/s00410-017-1418-1
This image from NASA’s Mars Curiosity rover shows the Amargosa Valley, on the slopes leading up to Mount Sharp on Mars. Credit: NASA / JPL-Caltech / MSSS
How good is your Martian geography? Does Valles Marineris ring a bell? This area is known for having landslides that are among the largest and longest in the entire solar system. They make the perfect object of study due to their steep collapse close to the scarp, extreme thinning, and long front runout. In a new research paper published in EPJ Plus, Fabio De Blasio and colleagues from Milano-Bicocca University, Italy, explain the extent to which ice may have been an important medium of lubrication for landslides on Mars. This can in turn help us understand the geomorphological history of the planet and the environment of deposition.
The authors noted that the landslides in Valles Marineris are of similar shape as ice-lubricated landslides on Earth. In their paper, they feed these observations, combined with remote sensing measurements showing the presence of massive ice under the soil, into a numerical simulation exploring the possibility that such landslides were lubricated by ice.
They then explore two possible scenarios to explain what happens to landslides rocks: one in which ice is only present at the base, and another in which ice impregnates the soil. To reproduce the vertical collapse of landslide material in the landslide scarp area and the extreme thinning and runout in the front, the model must take into account the presence of ice in the calculations.
The authors, therefore, demonstrate how the presence of ice, exposed on the ground or in the collapsing slope, could affect the shape and velocity of these landslides. The calculated velocity of landslides are often well in excess of 100 m/s and up to 200 m/s at peak. The authors then compare the results of the numerical simulations with real images and elevation profiles, allowing them to draw conclusions regarding the influence of the climate on shaping Martian landscapes.
Reference:
Fabio Vittorio De Blasio, Giovanni Battista Crosta. Modelling Martian landslides: dynamics, velocity, and paleoenvironmental implications. The European Physical Journal Plus, 2017; 132 (11) DOI: 10.1140/epjp/i2017-11727-x
Note: The above post is reprinted from materials provided by Springer.
This HiRISE image cutout shows Recurring Slope Lineae in Tivat crater on Mars in enhanced color. The narrow, dark flows descend downhill (towards the upper left). Analysis shows that the flows all end at approximately the same slope, which is similar to the angle of repose for sand. Credit: NASA/JPL/University of Arizona/USGS
Dark features previously proposed as evidence for significant liquid water flowing on Mars have now been identified as granular flows, where sand and dust move rather than liquid water, according to a new article published in Nature Geoscience by the U.S. Geological Survey.
These new findings indicate that present-day Mars may not have a significant volume of liquid water. The water-restricted conditions that exist on Mars would make it difficult for Earth-like life to exist near the surface of the planet.
Scientists from the USGS, the University of Arizona, Durham University (England) and the Planetary Science Institute analyzed narrow, down-slope trending surface features on Mars that are darker than their surroundings, called Recurring Slope Lineae, or RSL. These RSL features grow incrementally, fade when inactive and recur annually during the warmest time of year on Mars. RSL are mostly found on steep rocky slopes in dark regions of Mars, such as the southern mid-latitudes, Valles Marineris near the equator, and in Acidalia Planitia on the northern plains. The appearance and growth of these features resemble seeping liquid water, but how they form remains unclear, and this research demonstrated that the RSL flows seen by HiRISE are likely moving granular material like sand and dust.
“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand,” said USGS scientist and lead author Colin Dundas. “This new understanding of RSL supports other evidence that shows that Mars today is very dry.”
The terminal end of the RSL slopes, said Dundas, are identical to the slopes of sand dunes where movement is caused by dry granular flows. Water almost certainly is not responsible for this behavior, which would require the volume of liquid to correspond to the length of slope available, producing more liquid on longer slopes. Instead, the 151 RSL examined by the study authors all end on similar slopes despite very different lengths. Additionally, said the scientists, water is unlikely to be produced only near the tops of slopes at these angles and if it were, it should be able to flow onto lower slopes.
This new research finds that these RSL features are flows of granular material and thus, align with the long-standing hypothesis that the surface of Mars lacks flowing water. Small amounts of water could still be involved in their initiation in some fashion, as hydrated minerals have been detected at some RSL locations. The authors conclude that liquid on present-day Mars may be limited to traces of dissolved moisture from the atmosphere and thin films of water.
Reference:
Colin M. Dundas, Alfred S. McEwen, Matthew Chojnacki, Moses P. Milazzo, Shane Byrne, Jim N. McElwaine, Anna Urso. Granular flows at recurring slope lineae on Mars indicate a limited role for liquid water. Nature Geoscience, 2017; DOI: 10.1038/s41561-017-0012-5
Moon crust formation graphic. Credit: The University of Texas at Austin/Jackson School of Geosciences
The Earth’s Moon had a rough start in life. Formed from a chunk of the Earth that was lopped off during a planetary collision, it spent its early years covered by a roiling global ocean of molten magma before cooling and forming the serene surface we know today.
A research team led by The University of Texas at Austin Jackson School of Geosciences took to the lab to recreate the magmatic melt that once formed the lunar surface and uncovered new insights on how the modern moonscape came to be. Their study shows that the Moon’s crust initially formed from rock floating to the surface of the magma ocean and cooling. However, the team also found that one of the great mysteries of the lunar body’s formation – how it could develop a crust composed of just one mineral – cannot be explained by the initial crust formation and must have been the result of some secondary event.
The results were published on Nov. 21 in the Journal for Geophysical Research: Planets.
“It’s fascinating to me that there could be a body as big as the Moon that was completely molten,” said Nick Dygert, an assistant professor at the University of Tennessee, Knoxville who led the research while a postdoctoral researcher in the Jackson School’s Department of Geological Sciences. “That we can run these simple experiments, in these tiny little capsules here on Earth and make first order predictions about how such a large body would have evolved is one of the really exciting things about mineral physics.”
Dygert collaborated with Jackson School Associate Professor Jung-Fu Lin, Professor James Gardner and Ph.D. student Edward Marshall, as well as Yoshio Kono, a beamline scientist at the Geophysical Laboratory at the Carnegie Institution of Washington.
Large portions of the Moon’s crust are made up of 98 percent plagioclase—a type of mineral. According to prevailing theory, which the study calls into question, the purity is due to plagioclase floating to the surface of the magma ocean over hundreds of millions of years and solidifying into the Moon’s crust. This theory hinges on the magma ocean having a specific viscosity, a term related to the magma’s “gooiness,” that would allow plagioclase to separate from other dense minerals it crystallized with and rise to the top.
Dygert decided to test the plausibility of this theory by measuring the viscosity of lunar magma directly. The feat involved recreating the molten material in the lab by flash melting mineral powders in Moon-like proportions in a high pressure apparatus at a synchrotron facility, a machine that shoots out a concentrated beam of high energy X-rays, and then measuring the time it took for a melt-resistant sphere to sink through the magma.
“Previously, there had not been any laboratory data to support models,” said Lin. “So this is really the first time we have reliable laboratory experimental results to understand how the Moon’s crust and interior formed.”
The experiment found that the magma melt had a very low viscosity, somewhere between that of olive oil and corn syrup at room temperature, a value that would have supported plagioclase flotation. However, it would have also led to mixing of plagioclase with the magma, a process that would trap other minerals in between the plagioclase crystals, creating an impure crust on the lunar surface. Because satellite-based investigations demonstrate that a significant portion of the crust on the Moon’s surface is pure, a secondary process must have resurfaced the Moon, exposing a deeper, younger, purer layer of flotation crust. Dygert said the results support a “crustal overturn” on the lunar surface where the old mixed crust was replaced with young, buoyant, hot deposits of pure plagioclase. The older cruse could have also been eroded away by asteroids slamming into the Moon’s surface.
Dygert said the study’s results exemplify how small-scale experiments can lead to large-scale understanding of geological processes that build planetary bodies in our solar system and others.
“I view the Moon as a planetary lab,” Dygert said. “It’s so small that it cooled quickly, and there’s no atmosphere or plate tectonics to wipe out the earliest processes of planetary evolution. The concepts described here could be applicable to just about any planet.”
Reference:
Nick Dygert et al, A Low Viscosity Lunar Magma Ocean Forms a Stratified Anorthitic Flotation Crust With Mafic Poor and Rich Units, Geophysical Research Letters (2017). DOI: 10.1002/2017GL075703
The surface of riverbeds tend to be covered with relatively large rocks, a protection against erosion. Penn geophysicists used a concept from granular physics to explain why this is the case. Credit: Frank Garvock
Pop the top off a can of mixed nuts and, chances are, Brazil nuts will be at the top. This phenomenon, of large particles tending to rise to the top of mixtures while small particles tend to sink down, is popularly known as the “Brazil nut effect” and more technically as granular segregation.
Look down at the top of a riverbed and it’s easy to draw a parallel: the top of a riverbed is typically lined with larger cobbles, while finer sand and small gravel particles make up the deeper layers.
Physicists concerned with particle movement have given a lot of thought to the mechanics by which particles sort in these types of scenarios, but that research has not been translated to earth science until now. In a new study, geophysicists from the University of Pennsylvania found that granular segregation helps explain the tendency of riverbeds to be lined by, or “armored” with, a layer of relatively larger particles.
Published in the journal Nature Communications, the findings enhance understanding of how riverbeds form, with implications for how rivers may also erode. But the research also makes new insights into the fundamental physics of particle segregation, which apply to all sorts of granular materials, from riverbeds and soils to industrial and pharmaceutical substances.
“There has been this granular segregation phenomenon that has been studied for decades,” said Douglas J. Jerolmack, associate professor in the Department of Earth and Environmental Science in Penn’s School of Arts and Sciences, “and then there’s this separate explanation by geologists and engineers about why riverbeds get a coarse layer on the surface, and the two had never met before. Our major contribution here is really taking the granular physics understanding of the segregation of particles — how big particles segregate and move up to the surface — and introducing it to the river problem.”
Jerolmack collaborated on the work with postdoctoral researchers Behrooz Ferdowsi, now at Princeton University; Carlos P. Ortiz, now at Deloitte Consulting; and Morgane Houssais, now at the City University of New York. Riverbed armoring is seen almost universally and is understood to be a way that rivers prevent excessive erosion.
“We call this armoring because the larger particles are like an armor that protects the riverbed underneath from getting eroded,” Jerolmack said. “If there are big cobbles that are lining the riverbed, then I’ll need a big flood in order to move them.”
Geologists have generally thought that fluid mechanics controls this pattern. The river water would wash away the finer particles, leaving the larger particles behind.
But the Penn-led team recognized that this explanation failed to conceive of the riverbed as a granular system, which would also be subject to the Brazil nut effect, not just the shear force of water.
To see if granular segregation did apply in a fluid system, the researchers turned to a laboratory stand-in for a river: a doughnut-shaped channel filled with large and small spherical particles. The lid of the channel pushes the fluid atop the particles, replicating the flow of a river.
As they had shown in an earlier study, particles move along the riverbed by two mechanisms: those at the top are pushed by the flow of liquid, while those deeper down creep along slowly due to the interaction among particles.
In the new work, the Penn team wanted to understand how these particles moved not just horizontally but also vertically in the bed.
Using their custom-built channel and fluid embedded with a fluorescent dye, Jerolmack and colleagues were able to scan through the entire depth of the channel and visualize the entire plane of particles, even those buried under several dozen other particles.
“It’s almost like taking an X-ray of our granular sample but with a laser and photographs,” Jerolmack said.
With the help of a software program, they were able to then track the horizontal and vertical positions of all of these particles through time. And they saw the Brazil nut effect in action.
“In this laboratory experiment of a very simplified river,” Jerolmack said, “we saw that, when we have a liquid pushing grains on the riverbed, those grains push grains underneath them that push grains that are underneath them and so on, and it creates this jostling motion that allows large particles to kind of float up. So we confirmed that this general behavior that is seen in granular systems seems to also occur in rivers.”
Another major finding, confirmed by computer simulations that account for the friction felt by each particle in the riverbed, was that this segregation of particles by size played out in two stages. In the first, the larger particles near the surface of the riverbed moved up, while those packed in the deeper parts of the bed appeared to remain almost motionless. But in a second stage, these creeping, deeper grains began to sort, the large ones occasionally getting sucked up into the faster flowing particles toward the top of the river bed and jostling upward.
“Basically no one had gone looking to see if exceedingly slow-moving granular materials contributed to segregation,” Jerolmack said. “The observation that we did see segregation happening, that coarse particles were moving up from this creeping layer, is brand new to science and also has all sorts of implications. It might explain how we see segregation happening in slow-moving places like soils on a hillside, where we tend to find coarse particles at the surface, despite there being no fluid force moving over them.”
Researchers have found it difficult to predict when rivers erode, or when hillsides dissolve into landslides, and these findings may help explain why these predictions have proved so elusive.
“We’ve been working on these problems for 100 years, and we still can’t predict with much certainty what fluid force is going to cause grains to start eroding,” Jerolmack said. “And that point changes through time. River-engineering projects, bridges and buildings all rely on estimates of the erosion threshold. I think we need to start from scratch with a new framework that incorporates granular physics.”
While these experiments and simulations can’t provide an exact replication for the complex conditions seen in rivers, such as turbulence, Jerolmack notes that the findings point to a need for integrating earth science with fundamental physics research to advance knowledge in both spheres.
“Our inability to predict when erosion will occur, our inability to predict when a slow, oozing pile of dirt on a hill will suddenly become a landslide, is because we are up against our limit of the fundamental understanding of how disordered materials behave,” Jerolmack said. “We need to advance our understanding of fundamental physics of disordered materials in order to have any shot at making predictions in the earth-materials realm. And this is one problem where I think we’ve made a start at doing that.
“Penn is an ideal place to do this,” he said. “Here there are a large number of physicists and engineers with a broad and interdisciplinary view of materials science. Collaborations facilitated by the Materials Research Science and Engineering Center have made this kind of work possible.”
The study was supported by the United States Army Research Office (Grant 64455EV) and National Science Foundation (grants EAR-1224943, EAR-1344280 and DMR-1120901).
Reference:
Behrooz Ferdowsi, Carlos P. Ortiz, Morgane Houssais, Douglas J. Jerolmack. River-bed armouring as a granular segregation phenomenon. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-01681-3
Photo of early stages of the eruption of the Sarychev on June 12, 2009. Image from the International Space Station of. Image courtesy of Earth Sciences and Image Analysis Laboratory, National Aeronautics and Space Administration (NASA) Johnson Space Center. NASA Photo ID: ISS020-E-9048. Credit: NASA
Volcanic eruptions emit sulfate aerosols via volcanic plumes, which may stay in the stratosphere for months to years, reflecting sunlight back into space, cooling the Earth’s lower atmosphere or troposphere over a long time period. It is traditionally believed that because of atmospheric circulation patterns, eruptions in the tropics could have an effect on the climate in both hemispheres while eruptions at mid or high latitudes only have impact over the hemisphere where they erupt.
“Well, it is not always the case,” says Dr. Xue Wu, the corresponding author of a recently published study in Atmospheric Chemistry and Physics. “We have found evidence showing that a high-latitude volcano can enhance the aerosol layer in the tropical stratosphere, and also have impact on the climate of both hemispheres.”
WU is from the Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences. She worked with Dr. Sabine Griessbach and Dr. Lars Hoffmann from Jülich supercomputing center, Forschungszentrum Jülich, Germay on a high-latitude volcanic eruption case. They used the Lagrangian particle dispersion model—MPTRAC and multi-source satellite observations to study the transport of volcanic aerosol from the high-latitude volcanic eruption Sarychev (48°N, 153°E).
The study revealed that when the Sarychev volcano erupted in June 2009, the Asian summer monsoon (ASM) anticyclonic circulation was developing. The anticyclonic circulation facilitated the meridional transport of aerosols from the extratropical upper troposphere/lower stratosphere to the tropical tropopause region. Then, the aerosols ascended slowly in the upward branch of the Brewer-Dobson circulation (BDC), the primary circulation in the stratosphere, and dispersed with the poleward branches of the BDC to both hemispheres. With the help of the ASM anticyclonic circulation, this high-latitude volcanic eruption will not only influence the climate in the northern hemisphere where the Sarychev located, but also have impact on the southern hemisphere, just as a tropical eruption does.
Based on their calculation, although there was only about 4 percent of the total SO2 from the Sarychev eruption (1.2±0.2106 tons) transported to the tropical stratosphere, it would result in 6 ±1104 tons of sulfate aerosol, which is several times higher than the 1.5-2104 tons per year required to explain the increase trend of the tropical stratospheric aerosol. On the contrary, if the Sarychev erupted in winter, the aerosol would be confined to the polar side of the strong subtropical jets, deposited or be washed out from the atmosphere in a relatively short time.
WU says, “It’s all about timing. If a high-latitude volcano erupts when the ambient atmospheric conditions are favorable for transport, it is well worth more attention.”
In the past decade, the Sarychev eruption in 2009 was not the only case of the ASM circulation transporting sulfate aerosol to the tropical stratosphere. “We may expect more in the future,” says Wu.
Reference:
Xue Wu et al, Equatorward dispersion of a high-latitude volcanic plume and its relation to the Asian summer monsoon: a case study of the Sarychev eruption in 2009, Atmospheric Chemistry and Physics (2017). DOI: 10.5194/acp-17-13439-2017
Fossil of Dipteronia brownii and extant Dipteronia browni. Credit: DING Wenna
Dipteronia (Sapindaceae) is an ancient relictual woody genus in East Asia and is endemic to southern and central China with two extant species: Dipteronia sinensis and Dipteronia dyeriana.
Compared to its modern restricted distribution, Dipteronia was present in the Far East and North America during the Palaeogene. However, when Dipteronia migrated to China and where it came from were still unknown due to the lacking fossil record.
In a new study published in Review of Palaeobotany and Palynology, researchers from Paleoecology Group of Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences present a newly discovered fossil occurrence of Dipteronia fruits from the early Oligocene (about 33.9 million to 23 million years ago) of Yunnan, southwestern China.
They collected fossil dicotyledonous leaves and two winged fruits of Dipteronia in lacustrine mudstones near Lühe Town (25°8.5′N, 101°22.5′E,), Chuxiong Yi Autonomous Prefecture, Yunnan Province.
They studied the fossil fruits morphologically and compared with both extant and fossil representatives of Dipteronia.
The fossils show combined characteristics of Dipteronia sinensis and Dipteronia brownii and fall within the range of morphological variability of D. brownii. Therefore, the researchers adopt a broad circumscription and assign their fossils to D. brownii.
Dipteronia fruit fossils fall within the range of variation in general size and shape of Dipteronia sinensis, which demonstrates that the genus has retained its unique fruit morphology since the Palaeogene.
Therefore, the central and southern regions of China, which experienced relative tectonic and climatic stability, provided suitable habitats for these palaeoendemic taxa
The new fossil discovery suggests that the palaeoendemic genus Dipteronia was widely distributed in North America and Asia during the Palaeogene, and had existed in southwestern China by the Rupelian.
Reference:
An early Oligocene occurrence of the palaeoendemic genus Dipteronia (Sapindaceae) from Southwest China. DOI: 10.1016/j.revpalbo.2017.11.002
Seismic record captured by the seismometer installed in the ICTJA-CSIC during the Bruce Springsteen concert at Camp Nou on May 14, 2016. The upper panel shows the seismogram, while the lower panel shows the spectrogram where it is possible to see the distribution of the energy between the different frequencies. You can distinguish the different songs of the concert and highlight those performed during the encores towards the end of the concert. Credit: Jordi Díaz
The last Bruce Springsteen’s concert in Barcelona was held on May 14, 2016 at the Fc Barcelona Stadium. For more than 3 hours, 65,000 spectators who fulfilled the Camp Nou stadium danced to the sound of the songs performed by “The Boss”. A seismometer installed at the basement of the Institute of Earth Sciences Jaume Almera of the CSIC (ICTJA-CSIC), located just 500 meters from the stadium, recorded the vibrations of the ground caused by coordinated jumping of the audience while dancing Springsteen’s songs. This is one of the cases analyzed by a team of researchers from the ICTJA-CSIC in a study on urban seismology that has been published in the journal Scientific Reports.
In the paper, researchers haves identified the source of some of the signals recorded in recent years by a seismic station installed in the ICTJA building. The authors have verified that the seismometer has been able to detect the earth shacking generated by phenomena linked to human activity such as the subway activity, traffic, the celebration of goals during certain football matches, concerts and even fireworks launched from the vicinity of the Institute.
“Current seismometers are very sensitive devices, and they are able to register all kind of signals. Within the city, human activity produces a large number of detectable vibrations and earth shakings. If we treat and analyze the recorded seismic signal we’re able to stablish the source which originated it”, explains the researcher of the ICTJA-CSIC and first author of the study Jordi Díaz that remembers that these vibrations “are imperceptible for humans”.
Díaz remembers that the seismometer was installed in the building with an scientific dissemination purpose. “Over the years we have seen that the station registered curious and weird seismic signals. This led us to ask ourselves about their causes “says the ICTJA-CSIC researcher.
Traffic, subway and soccer matches
The paper shows how the seismometer installed in the ICTJA-CSIC building is able to detect the traffic activity in the nearby Diagonal Avenue, one of the main Barcelona’s traffic entrance. Diaz says that “the signal shows the evolution of traffic throughout the week and between daytime and nighttime. We can see that the peaks occur mainly in rush hours. The signal shows the decrease of the traffic activity during the nighttime and in weekends”.
According to the article, the seismometer can also record the vibrations induced by tube trains along a subway line running beneath Diagonal Avenue (L3). “The Institute is located at a distance about 150 meters from the “Palau Reial” subway station so we can detect the individual passage of each train,” says Jordi Díaz. The authors were able to observe in the recorded signal “the variations in the frequency of the tube trains circulation throughout the day and during the entire week. We could see how the intervals between the peaks of maximum intensity of the seismic signal increase during night and in the weekends “.
The celebrations of the goals during soccer matches held in the Camp Nou can also be registered by the seismic station installed at ICTJA-CSIC. In the paper, the authors have also analyzed the signal generated by the reaction of the public to each of the three goals scored by FC Barcelona in the last 15 minutes of the first leg Champions League semifinals game against Bayern Munich in May 2015.
Díaz considers that the seismic signal recorded during the Bruce Springsteen performance is “one of the most interesting, since it contains a lot of information. The recorded data of earth vibrations also allows us to identify the different songs of the playlist because when the rhythm and intensity of the music change, the way the audience dance also changes “.
According to Diaz, this study evidences that “seismometers can be used as an easy-to-use complementary monitoring tool for certain processes related with the urban environment, such as road traffic or subway activity”.
The researcher considers that it has been ”interesting to see the difference between the vibrations generated by those celebrating a goal in the Camp Nou Stadium from those generated by a crowd dancing during a concert in the same sceneario. This analysis could provide, for example, interesting information to engineers on building’s behaviour “.
Reference:
J. Diaz, M. Ruiz, Pilar S. Sanchez-Pastor, P. Romero, (2017), Urban seismology: on the origin of earth vibrations within a city, Scientific Reports DOI: 10.1038 / s41598-017-15499-y
The Cascadia Subduction Zone is capable of generating powerful earthquakes. The study found compact sediments along the coast of Washington and northern Oregon, a result that suggests that the area could be more prone to producing larger quakes than subduction zone areas farther south with less compact sediments. Adapted from FEMA graphic. Credit: FEMA/Jackson School of Geosciences/UT Austin
The Cascadia Subduction Zone off the coast of the Pacific Northwest has all the ingredients for making powerful earthquakes — and according to the geological record, the region is due for its next “big one.”
A new study led by The University of Texas at Austin has found that the occurrence of these big, destructive quakes and associated devastating tsunamis may be linked to compact sediments along large portions of the subduction zone. In particular, they found that big, destructive quakes may have a better chance of occurring offshore of Washington and northern Oregon than farther south along the subduction zone — although any large quake would impact the surrounding area.
“We observed very compact sediments offshore of Washington and northern Oregon that could support earthquake rupture over a long distance and close to the trench, which increases both earthquake and tsunami hazards,” said lead author Shuoshuo Han, a postdoctoral fellow at the University of Texas Institute for Geophysics (UTIG). UTIG is a research unit of the Jackson School of Geosciences.
The findings, published in Nature Geoscience on Nov. 20, are important for understanding factors that influence earthquake and tsunami generation in Cascadia and at other subduction zones around the world. Researchers from Columbia University and Penn State University also contributed to the study.
Subduction zones are areas where one tectonic plate dives or “subducts” beneath another plate. The world’s most powerful earthquakes are produced at the interface between the two plates. At certain subduction zones, such as those in Cascadia, Sumatra and eastern Alaska, a thick sediment layer overlies the subducting oceanic plate. Some of the sediment is scraped off during subduction and piled up on the top plate, forming a thick wedge of material, while the rest of the sediment travels down with the bottom plate.
How the stress is built up and released at the plate interface is greatly influenced by the degree of compaction of both the sediment wedge and the sediment between the plates. To understand sediment compaction along Cascadia, Han and her collaborators conducted a seismic survey off the coast of Washington and Oregon that allowed the researchers to see up to four miles of sediment layers overlaying the subduction zone. This was accomplished by the using nearly five-mile-long seismic streamers, a scientific tool used to image the seafloor using soundwaves.
“These kinds of long-streamer marine seismic studies provide the best tools available to the science community to efficiently probe subduction zones in high resolution,” said co-author Suzanne Carbotte, a research professor at Columbia University.
Combining the seismic data with measurements from sediment samples previously retrieved from this region through ocean drilling, they found that while the thickness of the incoming sediment is similar offshore of Washington and Oregon, the compaction is very different. Off the coast of Washington and northern Oregon, where almost all of the sediments glom on to the top plate and are incorporated into the wedge, the sediments were tightly packed together without much water in the pore space between the sediment grains — an arrangement that can make the plates more prone to sticking to each other and building up high stress that can be released as a large earthquake. In turn, the compacted sediments could boost the ability of large earthquakes to trigger large tsunamis because the sediments are able to stick and move together during earthquakes. This can boost their ability to move massive amounts of overlying seawater.
“That combination of both storing more stress and the ability for it to propagate farther is important for both generating large earthquakes and for propagating to very shallow depths,” said Nathan Bangs, a senior research scientist at UTIG and study co-author.
The propagation of earthquakes into shallow depths is what causes large tsunamis like the one that followed the Magnitude 9.0 earthquake that struck Tohoku, Japan in 2011.
In contrast, off the coast of central Oregon, the thick layer of subducting sediments are less compact, with water in the pore space between the grains. This arrangement prevents the plates from sticking as much, and allows them to rupture with less stress accumulated-thereby generating smaller earthquakes.
The Cascadia Subduction Zone generates a large earthquake roughly every 200 to 530 years. And with the last large earthquake occurring in 1700, scientists are expecting a large quake to occur in the future, although it’s impossible to pinpoint the timing exactly. The research findings can help scientists understand more about the features that make some areas of subduction zones better earthquake incubators than others.
“The results are consistent with existing constraints on earthquake behavior, offer an explanation for differences in structural style along the margin, and may provide clues about the propensity for shallow earthquake slip in different regions,” said co-author Demian Saffer, a Penn State University professor.
The study was funded by the National Science Foundation.
Reference:
Shuoshuo Han, Nathan L. Bangs, Suzanne M. Carbotte, Demian M. Saffer, James C. Gibson. Links between sediment consolidation and Cascadia megathrust slip behaviour. Nature Geoscience, 2017; DOI: 10.1038/s41561-017-0007-2
Some of the coldest and darkest dust in space shines brightly in this infrared image from the Herschel Observatory. Credit: ESA/NASA/JPL-Caltech
Life on our planet might have originated from biological particles brought to Earth in streams of space dust, a study suggests.
Fast-moving flows of interplanetary dust that continually bombard our planet’s atmosphere could deliver tiny organisms from far-off worlds, or send Earth-based organisms to other planets, according to the research.
The dust streams could collide with biological particles in Earth’s atmosphere with enough energy to knock them into space, a scientist has suggested.
Such an event could enable bacteria and other forms of life to make their way from one planet in the solar system to another and perhaps beyond.
The finding suggests that large asteroid impacts may not be the sole mechanism by which life could transfer between planets, as was previously thought.
The research from the University of Edinburgh calculated how powerful flows of space dust — which can move at up to 70 km a second — could collide with particles in our atmospheric system.
It found that small particles existing at 150 km or higher above Earth’s surface could be knocked beyond the limit of Earth’s gravity by space dust and eventually reach other planets. The same mechanism could enable the exchange of atmospheric particles between distant planets.
Some bacteria, plants and small animals called tardigrades are known to be able to survive in space, so it is possible that such organisms — if present in Earth’s upper atmosphere — might collide with fast-moving space dust and withstand a journey to another planet.
The study, published in Astrobiology, was partly funded by the Science and Technology Facilities Council.
Professor Arjun Berera, from the University of Edinburgh’s School of Physics and Astronomy, who led the study, said: “The proposition that space dust collisions could propel organisms over enormous distances between planets raises some exciting prospects of how life and the atmospheres of planets originated. The streaming of fast space dust is found throughout planetary systems and could be a common factor in proliferating life.”
Reference:
Arjun Berera. Space Dust Collisions as a Planetary Escape Mechanism. Astrobiology, 2017; DOI: 10.1089/ast.2017.1662
Oxygen has provided a breath of fresh air to the study of the Earth’s evolution some 400-plus million years ago.
A team of researchers, including a faculty member and postdoctoral fellow from Washington University in St. Louis, found that oxygen levels appear to increase at about the same time as a three-fold increase in biodiversity during the Ordovician Period, between 445 and 485 million years ago, according to a study published Nov. 20 in Nature Geoscience.
“This oxygenation is supported by two approaches that are mostly independent from each other, using different sets of geochemical records and predicting the same amount of oxygenation occurred at roughly the same time as diversification,” said Cole Edwards, the principal investigator of a study conducted when he was a postdoctoral fellow in the lab under the paper’s senior author, David Fike, associate professor in Earth and Planetary Sciences in Arts & Sciences. The other authors are Matthew Saltzman of Ohio State University and Dana Royer of Wesleyan University in Connecticut.
“We made another link between biodiversification and oxygen levels, but this time during the Ordovician where near-modern levels of oxygen were reached about 455 million years ago,” said Edwards, assistant professor in geological and environmental sciences at Appalachian State in Boone, N.C. “It should be stressed that this was probably not the only reason why diversification occurred at that time. It is likely that other changes — such as ocean cooling, increased nutrient supply to the oceans and predation pressures — worked together to allow animal life to diversify for millions of years.”
This explosion of diversity, recognized as the Great Ordovician Biodiversification Event, brought about the rise of various marine life, tremendous change across species families and types, as well as changes to the Earth, starting at the bottom of the ocean floors. Asteroid impacts were among the many disruptions studied as the reasons for such an explosion of change. Edwards, Fike and others wanted to continue to probe the link between oxygen levels in the ocean-atmosphere and diversity levels of animals through deep time.
Estimating such oxygen levels is particularly difficult: There is no way to directly measure the composition of ancient atmospheres or oceans. Time machines exist only in fiction.
Using geochemical proxies, high-resolution data and chemical signatures preserved in carbonate rocks formed from seawater, the researchers were able to identify an oxygen increase during the Middle and Late Ordovician periods — and a rapid rise, at that. They cite a nearly 80-percent increase in oxygen levels where oxygen constituted about 14 percent of the atmosphere during the Darriwilian Stage (Middle Ordovician 460-465 million years ago) and increased to as high as 24 percent of the atmosphere by the mid-Katian (Late Ordovician 450-455 million years ago).
“This study suggests that atmospheric oxygen levels did not reach and maintain modern levels for millions of years after the Cambrian explosion, which is traditionally viewed as the time when the ocean-atmosphere was oxygenated,” Edwards said. “In this research, we show that the oxygenation of the atmosphere and shallow ocean took millions of years, and only when shallow seas became progressively oxygenated were the major pulses of diversification able to take place.”
The chemical signatures that served as proxies for dissolved inorganic carbon included data from geologic settings ranging from the Great Basin in the western United States, to the northern and eastern U.S., to Canada and its Maritimes, as well as Argentina in the Southern Hemisphere and Estonia in the Eastern Hemisphere. Nevada, Utah, Oklahoma, Missouri (New London north and Highway MM south of St. Louis), Iowa, Ohio, West Virginia and Pennsylvania were among the data points across the U.S.
The researchers concluded that it remained unclear whether the increased oxygenation had a direct effect on animal life, or even if it had a passive effect by, say, expanding the oxygen-rich ecospace. So it is difficult to resolve if temperature, increased oxygenation or something else served as the driver for biodiversification. But the findings showed that oxygen certainly was spiking during the times of some of the greatest change.
“Oxygen and animal life have always been linked, but most of the focus has been on how animals came to be,” said Saltzman, professor and school director of Earth Sciences at Ohio State. “Our work suggests that oxygen may have been just as important in understanding how animals came to be so diverse and abundant.”
Reference:
Cole T. Edwards, Matthew R. Saltzman, Dana L. Royer, David A. Fike. Oxygenation as a driver of the Great Ordovician Biodiversification Event. Nature Geoscience, 2017; DOI: 10.1038/s41561-017-0006-3
Kaolinite sinks into the subduction zone with the oceanic plate. As it changes into the newly discovered phase it takes in water from its surroundings and releases it upon further structure change down in the mantle. Credit: Wikimedia Commons, MagentaGreen (modified) CC BY SA 3.0
The first observation of a super-hydrated phase of the clay mineral kaolinite could improve our understanding of processes that lead to volcanism and affect earthquakes. In high-pressure and high-temperature X-ray measurements that were partly conducted at DESY, scientists created conditions similar to those in so-called subduction zones where an oceanic plate dives under the continental crust. The transport and release of water during subduction causes strong volcanic activity. An international team led by scientists of Yonsei University in the Republic of Korea, presents the results in the scientific journal Nature Geoscience.
In a subduction zone, a heavy oceanic plate meets a second, lighter continental plate and moves under it and into the earth’s mantle. With the oceanic plate, water enters the earth as it is trapped in minerals of the oceanic crust or overlaying sediments. These minerals slowly sink deeper into the mantle over millions of years. With increasing depth, temperature and pressure, the minerals become instable, break down and transform into new compounds.
During these transformations, water is released and rises into the surrounding, hotter mantle where it decreases the melting temperature of the mantle rock. “When the mantle rocks melt, magma is generated. This can lead to volcanic activity when the magma rises to the surface,” explains Yongjae Lee from Yonsei University who led the study. “While we know that the water cycle in subduction zones influences volcanism and possibly seismicity, we don’t know much about the processes that form this cycle.”
Since these processes take place many kilometres under Earth’s surface, it is impossible to observe them directly. Even the Kola Superdeep Borehole in Russia, the deepest borehole on Earth, reaches no deeper than 12,262 metres. One way to learn more about the transformations in greater depths of subduction zones is to create similar conditions in the laboratory. High-pressure and high-temperature measurements allow scientists to take a close look at the structural changes in the different minerals that form the crust and sediments.
One of these minerals is kaolinite, a clay mineral containing aluminium that is an important part of the oceanic sediments. The scientists were now able to observe the formation of a new phase of the mineral, so-called super-hydrated kaolinite. They examined a sample of kaolinite in the presence of water at pressures and temperatures corresponding to those at different depths in subduction zones. With X-ray diffraction and infrared spectra measurements, structural and chemical changes were characterized.
At a pressure of circa 2.5 Giga-Pascal (GPa), more than 25,000 times the average pressure at sea level, and a temperature of 200 degrees Celsius, the super-hydrated phase was observed. These conditions are present at a depth of about 75 kilometres in subduction zones. In the new phase, water molecules are enclosed between the layers of the mineral. The super-hydrated kaolinite contains more water than any other known aluminosilicate mineral in the mantle. When pressure and temperature sink back to ambient conditions, the structure reverts to its original form.
In measurements carried out at the Extreme Conditions Beamline P02.2 at DESYs X-ray source PETRA III, the scientists examined the breakdown of the new phase at even higher pressures and temperatures. “Our beamline provides an environment to investigate samples at extreme pressures and temperatures. Using a so-called graphite resistive heated diamond anvil cell, we were able to observe the changes at a pressure of up to 19 Giga-Pascal and a temperature of up to 800 degrees,” says DESY-scientist Hanns-Peter Liermann of the Extreme Conditions Beamline who co-authored the study. The super-hydrated kaolinite broke down at 5 Giga-Pascal and 500 degrees, two additional transformations happened at higher pressures and temperatures. During these transformations, the water that was intercalated in the kaolinite is released.
The observation of the formation and breakdown of the super-hydrated kaolinite bears important information about the processes that occur over a depth range of about 75 kilometres to 480 kilometres in subduction zones. The release of water that takes place when the super-hydrated kaolinite breaks down could be an important part of the water cycle that causes volcanism along subduction zones. The breakdown probably happens below a depth of about 200 kilometres, the released water could then contribute to the formation of magma.
Additionally, the super-hydrated kaolinite could influence seismicity. During the formation of the new phase, the water that surrounds kaolinite is removed from the environment. This could change the friction between the subducting and the overlying slabs. The scientists assume that other minerals in the sediment or crust could undergo similar transformations. Thus, the study could improve the understanding of the geochemical processes in subduction zones of the earth.
Reference:
Huijeong Hwang, Donghoon Seoung, Yongjae Lee, Zhenxian Liu, Hanns-Peter Liermann, Hyunchae Cynn, Thomas Vogt, Chi-Chang Kao, Ho-Kwang Mao. A role for subducted super-hydrated kaolinite in Earth’s deep water cycle. Nature Geoscience, 2017; DOI: 10.1038/s41561-017-0008-1
Seed ferns reproduce via seeds instead of spores. This extinct group of trees carried large fernlike leaves as depicted on the image. A leaf print fossil of Macralethopteris, a seed fern present in the Jambi flora collection. Credit: Leiden University
Paleobotanist Menno Booi discovered that 250 previously described fossil tree species are objectively not distinguishable and belong to only one single species.
Towering clubmosses, primitive conifers and the first appearance of seed fern groups characterize the so-called Jambi flora. A collection of plant fossils that once grew in the Indonesian province of Jambi. Booi investigated this 290 million year old collection and made several discoveries.
The first expedition to the Jambi region took place in 1925. The team, consisting of a geologist and a biologist, collected many fossils. Once in the Netherlands, the fossils were described by paleobotanist W. Jongmans. “Back in the days the heart of the province of Jambi on Sumatra was still an inhospitable jungle and carrying out fieldwork was a real challenge. For example, the researchers needed to be cautious for the many tigers that still ruled the area,” Booi explains.
After a dormant existence of almost a century, the collection was rediscovered by Naturalis paleobotanist Isabel van Waveren. The revision of the specimens showed that the material was very unique, but also that many questions were still unanswered. The ecological preferences of the species found in the Jambi flora did not match: some species appeared to be from wet environments, while others where know to prefer a dry habitat. This renewed the interest of the researchers that it led to four expeditions to the original localities, in which new fossils were collected. Naturalis researcher Menno Booi was one of the team members.
He examined all the material collected during the expeditions, and it turned out that there were many old elements that were already known from the Carboniferous (300 till 350 million years ago). An example of these are clubmosses growing to 40 meters in height. Nowadays these do not exceed 20 centimetres. Clubmosses grew mainly in wet swampy conditions.
The recent material also contained many new elements. Such as seed ferns and primitive conifers with trunks of 2.5 meters in diameter. These plants felt at home in a dry environment. “Fossils of these plant groups appear in the Jambi flora for the first time,” says Booi.
There is a remarkable number of pieces of fossilized wood of conifers present in the Jambi collection. “At least 250 species have been described for this type of wood in the past,” says the paleobotanist. The wood itself has few characteristics. Descriptions are based almost entirely on measurements of the anatomy of the wood. For example, the diameter of tracheids, elongated cells that serve in the transport of water and mineral through the wood.
Booi compiled measurements into a large dataset and analysed them. He concluded that, contrary to expectations, there are no distinct species to discerned in this large collection of fossil wood and that the specimens instead belong to one species, which bears a wide variation in appearance.
Booi calls his results remarkable: “Apparently, the process of species description in paleobotany is quite arbitrary and new species are being described based on only a few specimens.” As part-time PhD student and full-time software developer, Menno Booi believes that this process should be altered and that present (computational) techniques offer numerous possibilities to do so. For example, he proposes machine learning as a new option. “You can actually teach software to recognize certain patterns in plant fossils. In this way, you standardize and classify in an objective way whether a specimen differs from other fossil material and to what extent it differs. Doing so makes the field of paleobotany more interesting, more concrete and even sexier,” says the researcher.
Jablonskipora kidwellae, the first known member of the modern bryozoans to grow up into a structure. Credit: Paul Taylor/London’s Natural History Museum
Lurking in oceans, rivers and lakes around the world are tiny, ancient animals known to few people. Bryozoans, tiny marine creatures that live in colonies, are “living fossils”—their lineage goes back to the time when multi-celled life was a newfangled concept. But until now, scientists were missing evidence of one important breakthrough that helped the bryozoans survive 500 million years as the world changed around them.
Today, the diverse group of bryozoans that dominate modern seas build a great range of structures, from fans to sheets to weird, brain-like blobs. But for the first 50 or 60 million years of their existence, they could only grow like blankets over whatever surface they happened upon.
Scientists recently announced the discovery of that missing evolutionary link—the first known member of the modern bryozoans to grow up into a structure. Called Jablonskipora kidwellae, it is named after UChicago geophysical scientists David Jablonski and Susan Kidwell.
Both are prominent scholars in their fields: Jablonski in origins, extinctions and other forces shaping biodiversity across time and space in marine invertebrates; Kidwell in the study of how fossils are preserved and the reliability of paleobiologic data, especially for detecting recent, human-driven changes to ecosystems. They also happen to be married.
“We were absolutely thrilled. What a treat and an honor, to have this little guy named after us,” said Jablonski, the William R. Kenan Jr. Distinguished Service Professor of Geophysical Sciences.
“I never expected to have a fossil named after me,” said Kidwell, the William Rainey Harper Professor in Geophysical Sciences, “and here it’s one that is an evolutionary breakthrough. We’re still smiling about it.”
Jablonskipora kidwellae lived about 105 million years ago, latching on to rocks and other hard surfaces in shallow seas—a bit like corals, though they’re not related. The fossils came from southwest England, along cliffs near Devon, originally collected in 1903 and analyzed by co-discoverers Paul Taylor and Silviu Martha from London’s Natural History Museum.
Bryozoans never figured out a symbiotic partnership with photosynthetic bacteria, as coral did, so their evolution took a different turn. Each one in a colony is genetically identical, but they have specialized roles, like ants or bees. Their shelly apartment complexes house thousands of the creatures, which have soft bodies with tiny tentacles to catch nutrients.
Growing upright was an evolutionary hack for Jablonskipora kidwellae, the two professors said: building bigger colonies extending upward from just a tiny attachment site was a good evolutionary move, allowing it to tap the water flowing above the sea floor—both for food and to scatter its offspring further. “This is a huge competitive advantage for them,” Jablonski said, “but it required some evolutionary organization to create a vertical structure.” Kidwell added: “This is the next level of cooperation among these individuals within the colony.”
They expressed a fondness for the creature, which they said was, like other bryozoans, “small and slow, but fierce.” Bryozoan fossils are sometimes found having bulldozed right over neighboring colonies in an intense battle for growing space. In a manner of speaking: this all would have taken place in extremely slow motion.
“They’re pretty fabulous little animals,” Kidwell said.
Jablonski and Kidwell have been friends with Taylor, one of the discoverers, since they spent summers on various research at the London Natural History Museum in the 1980s, but they said his news took them both completely by surprise. Jablonski had previously co-authored one paper with Taylor; Kidwell is currently collaborating with him on a study of bryozoan skeletal debris in modern sediments from the Channel Islands off Los Angeles.
It is the second honor of the year for both Kidwell and Jablonski: In April she received the Moore Medal from the Society for Sedimentary Geology, and in October he received the Paleontological Society Medal, that society’s highest honor.
Jablonski had one previous species named after him—a tiny clam—but Jablonskiporawill now be a genus in addition to a species.
Reference:
Silviu O. Martha et al, The oldest erect cheilostome bryozoan: Jablonskipora gen. nov. from the upper Albian of south-west England, Papers in Palaeontology (2017). DOI: 10.1002/spp2.1097
Recorded earthquakes in the region are marked with gray circles. Major fault lines are in blue, with the Nov. 12 epicenter marked by a star. Credit: Amir Salaree, CC BY-ND
With a magnitude of 7.3, the Nov. 12, 2017 earthquake that shook the border region between Iran and Iraq is among the largest ever recorded in this area. Seismologists know it resulted from the pressure built up between the colliding Arabian and Eurasian plates of the Earth’s crust. But there’s still a lot for researchers to uncover about seismic activity in the region.
Originally from Iran, I’m a seismologist who studies earthquakes, tsunamis and landslides. I’ve been thinking a lot about potential seismic activity and the consequent hazard in this area. My earth sciences colleagues have been examining these faults for years in order to better understand the fault systems in the region. However, the Earth sometimes surprises us, and this time the rupture did not happen on a previously known major fault.
Our lack of knowledge about the specific fault causing this earthquake is mainly because seismologists know only about faults that have already caused earthquakes. Only after new earthquakes can we update our fault maps to be more complete. It’s learning from past earthquakes that lets us better understand and prepare for future seismic hazards.
The outer rigid surface of the Earth is divided into chunks known as tectonic plates. These plates move around at the rate of a few centimeters per year – by coincidence, the same rate at which your fingernails grow. The Arabian Peninsula and Iran are on separate adjacent plates in this region.
The mostly northward continental collision between the Arabian plate and Eurasia (which includes Iran) has created the Zagros mountains as the plates crash together in slow motion. Collision energy is also released in the form of earthquakes at fault lines along or close to these boundaries. Many researchers are studying what portions of this region’s collision energy are spent building mountains versus causing earthquakes.
Seismologists do know the Zagros mountains host many active fault lines, and the tectonic wiggles on these faults cause a significant number of earthquakes in Iran and Iraq. In fact, about 25,000 earthquakes have been recorded in the Zagros mountains over just the past 11 years. Although these earthquakes are usually small in size, the data show that every now and then moderate to large events also occur; these can result in significant destruction.
The main fault responsible for the Nov. 12 earthquake has yet to be identified. As located by the Iranian Seismological Center, the quake took place in a zone between two major known faults: the High Zagros Fault and the Mountain Front Fault.
One good thing that comes from a big earthquake is more data about the structure of tectonic plates and therefore the seismic potential in the area. Researchers and planners can in turn use this information to prepare for future events. As the saying goes, we cannot predict earthquakes, but we can anticipate them.
What was different about this quake
Large earthquakes in Iran have typically caused a high number of fatalities. The 1990 Rudbar (magnitude 7.4) and 2003 Bam (magnitude 6.6) earthquakes resulted in a total of around 55,000 deaths and as much as US$9 billion of economic loss.
According to the Iranian state-run news agency, the Nov. 12 earthquake killed over 500 people, as of this publication, with thousands injured, mostly on the Iranian side of the border. Registering a magnitude of 7.3, the quake was comparable in size to its 1990 and 2003 counterparts, but produced a relatively low number of casualties. This was due to several important factors.
First, this latest earthquake was preceded by a much smaller magnitude 4.4 foreshock – a relatively smaller earthquake that precedes the largest earthquake in a series. The foreshock caused many people to leave their homes and, in effect, escape the subsequent destruction. As a seismologist would tell you, earthquakes don’t kill people; buildings do.
Secondly, it occurred on much more rigid ground cover – mostly rocks instead of thick layers of unconsolidated soil compared to the other two events. These geological conditions mean the seismic waves from the earthquake were less amplified, and so less shaking was observed on the surface.
Also, following the previous recent destructive earthquakes in Iran, the Iranian government passed new construction regulations for more earthquake-safe buildings, calling for such things as concrete and steel frames and detailed study of the base soil prior to the construction. Considering the alarming foreshock, the smaller population in the affected towns (compared to the former two destructive earthquakes) and the unknown extent of enforcement of the building codes, it is difficult to estimate how the number of casualties would have increased in the absence of these laws.
For a more complete picture of this earthquake, we still need more data that are yet to be collected and documented both from field surveys and the study of seismic waves recorded by seismometers throughout the world. Seismologists are looking for further evidence about the propagation of the earthquake rupture to learn more about the internal characteristics of the fault as well as the properties of the convergence between the Arabian and Eurasian plates. They’ll also use seismic waves recorded from this earthquake to image the structure of Earth’s crust in the region – just like an ultrasound that provides a picture of your internal organs.
The aftermath of a seismic event like this one is an excellent opportunity to evaluate our understanding of earthquakes and their hazards in Iran and Iraq as well as elsewhere around the world.
Note: The above post is reprinted from materials provided by The Conversation. The original article was written by Amir Salaree, Ph.D. Candidate in Earth and Planetary Sciences, Northwestern University
These are sedimentary rock layers chronicling Earth’s geological history. Credit: Georgia Tech / Yale / Reinhard / Planavsky
For researchers pursuing the primordial history of oxygen in Earth’s atmosphere, a new study might sour some “Eureka!” moments. A contemporary tool used to trace oxygen by examining ancient rock strata can produce false positives, according to the study, and the wayward results can mask as exhilarating discoveries.
Common molecules called ligands can bias the results of a popular chemical tracer called the chromium (Cr) isotope system, which is used to test sedimentary rock layers for clues about atmospheric oxygen levels during the epoch when the rock formed. Researchers at the Georgia Institute of Technology have demonstrated in the lab that many ligands could have created a signal very similar to that of molecular oxygen.
“There are some geographical locations and ancient situations where measurable signals could have been generated that had nothing to do with how much oxygen was around,” said Chris Reinhard, one of the study’s lead authors. Though the new research may impact how some recent findings are assessed, that doesn’t mean the tool isn’t useful overall.
“We’re not trying to revolutionize the way the tool is viewed,” said Yuanzhi Tang, who co-led the study. “This is about understanding its possible limitations to make discerning use of it in particular cases.”
Tang and Reinhard, both assistant professors of biogeochemistry in Georgia Tech’s School of Earth and Atmospheric Sciences, published their team’s results in a study on November 17, 2017, in the journal Nature Communications. Their work was funded by the NASA Astrobiology Institute, the NASA Exobiology program, and the Agouron Institute.
“On a global level, the chromium isotope system is still a great indicator of atmospheric oxygen levels through the ages,” Tang said. “The issue we exposed in the lab is more local with isolated samples, especially during eras when there wasn’t much atmospheric oxygen.”
Leaping ligands
Without a dominant oxygen presence, ligands likely made a great reactive substitute, as the researchers demonstrated in reactions with chromium. Like oxygen, ligands strongly attract electron pairs, which is what characterizes them as a chemical group.
And like reactions with oxygen, reactions with ligands enable metals like chromium to move around more easily in the world. In this case, the researchers were interested in organic ligands, ligands that contain carbon.
They were more apt to match oxygen’s mobility effect on chromium that made it end up as the signals in sedimentary rock that scientists, today, look for as a sign of ancient atmospheric oxygen.
Here’s roughly how the chromium isotope system works, followed by how organic ligands could make for false positives.
Chromium rollercoaster
The Earth is an enormous chemical laboratory performing reactions in conditions varying from arctic cold to volcanic heat, and from crushing ocean depths to no-pressure upper atmospheres. Winds and waves sweep around materials like turbulent conveyor belts, depositing some in sediments that later turn to stone.
Chromium’s ticket for the rollercoaster ride into sedimentary rock was usually an oxidizing agent that made it more soluble and better able to float, and atmospheric oxygen was an ideal oxidizer. The chemical reaction, which can be found in the study and involved manganese oxide handing off oxygens to chromium, would be a little like adding pontoons to chromium compounds.
For billions of years, Earth’s atmosphere was nearly devoid of O2, but after oxygen began increasing, especially in the last 800 million years, it became the domineering oxidizer. And characteristics of chromium deposits in ancient layers of rock became a great indicator of how much O2 was in the atmosphere.
Today, researchers test deep rock layer samples for the relation between two chromium isotopes, 52Cr, by far the most common Cr isotope, and 53Cr, to get a read on oxygen presence across geological eras.
“You powder the rock up; you dissolve it with acid, and then you measure the ratio of 53Cr to 52Cr in the material by using mass spectrometry,” Reinhard said. “It’s the ratio that matters, and it will be controlled by a range of complex processes, but generally speaking, elevated 53Cr in ocean sediment rock tends to indicate oxygen in the atmosphere.”
By the way, these Cr isotopes are stable and don’t undergo radioactive decay, thus the system does not work the way radiocarbon dating does, which relies on the decay of carbon 14.
Chemical imposter
In the lab, with a small assortment of organic ligands, Tang’s group showed that reactions of chromium with ligands led to 53Cr/52Cr signals that closely mimicked those stemming from oxygen-chromium reactions.
“Ligands have the capability to mobilize chromium as well,” Tang said. “In fact, ligands might be a significant factor in controlling chromium isotope signals in certain rock records.”
Organic ligands were probably around long before Earth’s atmosphere filled up with O2. And today, hundreds of millions of years after the reactions occurred, it’s basically impossible to find out if oxygen or ligands were at work.
Little discrepancies
If not accounted for, ligand reactions can distort small details in rock records about atmospheric oxygen, and they may have already.
Like paleontologists, who catalog ancient animal bones and other fossils, geologists keep massive, digitized archives of rock that they study to learn more about Earth’s ancient geological history. Scientists began testing physical samples of them with the Cr isotope system around 2009 and adding the results to the records.
“Since then, some discrepancies have turned up,” Reinhard said. “Ancient soil layers were showing evidence of oxygen when it probably shouldn’t have been there. Other samples from the same period weren’t showing that signal.”
But some researchers confronted with odd Cr signals have thought they had perhaps stumbled upon a radical find, and they developed explanations for how O2 may have been surprisingly bountiful on the lonesome spot where a particular rock layer formed, while molecular oxygen was scant on the rest of the globe. Others puzzled that atmospheric O2 levels may have risen much earlier than overwhelmingly broad evidence has indicated.
“A lot of that could be chalked up to other chemical processes and not to interactions with oxygen,” Reinhard said.
The study may serve as a cautionary tale about how to view Cr isotope data, especially when they leap off the page.
Reference:
Emily M. Saad, Xiangli Wang, Noah J. Planavsky, Christopher T. Reinhard, Yuanzhi Tang. Redox-independent chromium isotope fractionation induced by ligand-promoted dissolution. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-01694-y
The Central Iberian Peninsula was characterised by a very arid savanna during the middle Miocene, according to a study led by the Complutense University of Madrid (UCM) that compares the mammal assemblages from different localities in Africa and South Asia with those that inhabited the Iberian central area 14 million years ago.
The results of this study, recently published in PLOS ONE, are the product of more than fifteen years of fieldwork and previous paleontological studies of the fossil vertebrate remains found at the Somosaguas paleontological site (Madrid), which allowed paleontologists to infer the type of environment that existed in the middle Miocene in the central part of the Iberian Peninsula. This fossil site is located at the Somosaguas Campus of the UCM, a particular feature as only two paleontological sites have been discovered up to now at university campuses worldwide (the other one being located in the USA).
The body size of every species is largely influenced by the environmental conditions of the habitat where each species lives. For example, elephants that inhabit humid places (such as those in Asian jungles) are smaller than elephants that live in dry places (such as those that inhabit in African savannahs).
“Based on this premise, the distribution of sizes within a mammal community can offer us valuable information about its climatic context,” explains Iris Menéndez, a researcher at the Department of Paleontology of the UCM and the Institute of Geosciences (UCM and CSIC).
In this study paleontologists have been able to infer that the centre of the Iberian Peninsula witnessed a very arid tropical climate with a high precipitation seasonality. After a brief wet period, the annual dry season could last up to 10 months. “These results confirm the previous inferences on the Savannahs environment of Somosaguas in the Miocene, but placing this habitat at their driest estimated, within the limits between the savanna and the desert,” says Menéndez.
This study compiled the information of climatic parameters for more than 60 current localities from Africa and Asia, including information of the body size of the mammalian species that inhabit these localities.
“For this purpose, we made a compilation of information on mammalian fauna lists, their body sizes, and climatic parameters for these localities, such as temperatures and precipitation. Based on this data, we developed statistical models suitable for the inference of different climatic parameters in the past,” says the UCM researcher.
“We included the information on the 26 mammal species found in the Somosaguas site, which allowed us to infer the environment by comparison with the extant assemblages,” she adds.
Somosaguas is a particularly interesting fossil site in the context of paleoecological and paleoclimatic studies because it was located at a turning point during the Miocene. At this time, there was a marked change from warm and relatively humid global conditions to colder and arid environments. This inflection point eventually led to the beginning of the Pleistocene glaciations.
Moreover, the Somosaguas fossil site, due to its location within a university campus, gives to the general public the opportunity to visit it and learn all the details of the investigations that have been carried out from the data collected in the successive excavation campaigns.
Reference:
Iris Menéndez, Ana R. Gómez Cano, Blanca A. García Yelo, Laura Domingo, M. Soledad Domingo, Juan L. Cantalapiedra, Fernando Blanco, Manuel Hernández Fernández. Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event. PLOS ONE, 2017; 12 (10): e0186762 DOI: 10.1371/journal.pone.0186762
Sea glass and beach glass are similar but come from two different types of water. “Sea glass” is physically and chemically weathered glass found on beaches along bodies of salt water. These weathering processes produce natural frosted glass. “Genuine sea glass” can be collected as a hobby and can be used to make jewelry or make for decoration.”Beach glass” comes from fresh water and in most cases has a different pH balance, and has a less frosted appearance than sea glass. Sea glass takes 30 to 40 years, and sometimes as much as 100 years, to acquire its characteristic texture and shape. Sometimes also colloquially referred to as “Drift glass” from the longshore drift process that forms the smooth edges. In practice, the two terms are used interchangeably.
How is Sea Glass Formed?
Sea glass begins as normal shards of broken glass that are then persistently tumbled and ground until the sharp edges are smoothed and rounded. In this process, the glass loses its slick surface but gains a frosted appearance over many years.
Naturally produced sea glass (“genuine sea glass”) originates as pieces of glass from broken bottles, broken tableware, or even shipwrecks, which are rolled and tumbled in the ocean for years until all of their edges are rounded off, and the slickness of the glass has been worn to a frosted appearance.
Artificially produced sea glass (sometimes called “beach glass”), although superficially similar to sea glass, nevertheless has clear differences in appearance. Having not actually originated from the sea, most connoisseurs will not consider artificial “sea” glass to actually be genuine sea glass, but rather simply tumbled glass, where pieces of modern-day glass are tossed into a rock tumbler or dipped in acid to produce the desired finish. Artificially-produced, the glass is much less expensive and is used for making jewelry, but is often passed off as real sea glass.
What are Sea Glasses Colors?
The color of sea glass is determined by its original source. Most sea glass comes from bottles, but it can also come from jars, plates, windows, windshields, ceramics or sea pottery.
The most common colors of sea glass are kelly green, brown, and white (clear). These colors come from bottles used by companies that sell beer, juices, and soft drinks. The clear or white glass comes from clear plates and glasses, windshields, windows, and assorted other sources.
Where do you find sea glass?
Sea glass can be found all over the world, but the beaches of the northeast United States, Bermuda, Fort Bragg, California, Benicia, California, North Carolina beaches, Scotland, northwest England, Mexico, Hawaii, Dominican Republic, Puerto Rico, Nova Scotia, Australia, Italy and southern Spain are famous for their bounty of sea glass, bottles, bottle lips and stoppers, art glass, marbles, and pottery shards. The best times to look are during spring tides especially perigean and proxigean tides, and during the first low tide after a storm.
Where are the best beaches to find sea glass in United States?
Under Sumatra, the oceanic tectonic plate is descending below the continental plate. The complex geological structure of the layers of rock, combined with the splay faults, results in highly complicated rupture processes during an earthquake. Credit: Gabriel/Bader
Scientists in Munich have completed the first detailed simulation of the Sumatra earthquake that triggered a devastating tsunami on the day after Christmas in 2004. The results offer new insights into the underlying geophysical processes.
The Christmas 2004 Sumatra-Andaman earthquake was one of the most powerful and destructive seismic events in history. It triggered a series of tsunamis, killing at least 230,000 people. The exact sequence of events involved in the earthquake remains unclear.
A deeper understanding of the geophysical processes involved is now at hand, thanks to a simulation performed by a team of geophysicists, computer scientists and mathematicians from the Technical University of Munich (TUM) and LMU Munich on the SuperMUC supercomputer at the Leibniz Supercomputing Center (LRZ) of the Bavarian Academy of Sciences. This largest-ever rupture dynamics simulation of an earthquake could facilitate the development of more reliable early warning systems. The results of the simulation will be presented at the International Conference on High-Performance Computing, Networking, Storage and Analysis (SC 17) in Denver, Colorado, which began on November 12th.
In subduction zones – locations where tectonics plates meet at seams in the Earth’s crust, with one plate moving below the other – earthquakes occur at regular intervals. However, it is not yet precisely known under what conditions such “subduction earthquakes” can cause tsunamis or how big such tsunamis will be.
Earthquakes are highly complex physical processes. In contrast to the mechanical processes occurring at the rupture front, which take place on a scale of a few meters at most, the entire Earth’s surface rises and falls over an area of hundreds of square kilometers. During the Sumatra Earthquake, the tear in Earth’s crust extended for more than 1,500 km (approximately equivalent to the distance from Munich to Helsinki or Los Angeles to Seattle) – the longest rupturing fault ever seen. Within 10 minutes, the seafloor was vertically displaced by the earthquake by as much as 10 meters.
Simulation with over 100 billion degrees of freedom
To simulate the entire earthquake, the scientists covered the area extending from India to Thailand with a three-dimensional mesh consisting of over 200 million elements and incorporating more than 100 billion degrees of freedom.
The size of the elements varied according to the required resolution: A much finer mesh was used along the fault in order to resolve the complex frictional processes, and on the surface so as to take into account the topographical features and the relatively low-velocity seismic waves found there. In areas with little complexity and fast waves, a coarser mesh was employed.
To calculate the pattern of seismic wave propagation, more than three million time steps had to be computed over the smallest elements. As input data, the team used all available information on the geological structure of the subduction zone and the initial conditions on the seafloor, as well as laboratory experiments on rock fracturing behavior.
In addition to the large so-called megathrust plate boundary, the scientists considered three smaller splay faults, or branching faults, suspected of having strongly impacted the tsunami-triggering deformation of the ocean floor.
Almost 50 trillion operations
“To make it possible to finish the simulation on SuperMUC within a reasonable period of time, it ultimately took five years of preparations to optimize our SeisSol earthquake simulation software. Just two years ago, the computing time for the simulation would have been 15 times longer,” explains Michael Bader, a professor of informatics at TUM.
All of the algorithmic components, from data input and output and the numerical algorithms used to solve the physical equations through to the parallel implementation on thousands of multicore processors, had to be optimized for the SuperMUC.
The Sumatra simulation still took almost 14 hours of processing time on all 86,016 cores of the SuperMUC, which performed nearly 50 trillion operations (almost 1015 operations per second, or around 1 petaflop/s – one-third of the theoretical maximum computing performance).
The largest and longest earthquake simulation ever performed
“We successfully completed the largest earthquake simulation of itskind ever seen,” says LMU geophysicist Dr. Alice-Agnes Gabriel. “With a duration of around eight minutes, it is also the longest. On top of that, it was the first-ever physics-based scenario for a real subduction rupture process. With the simultaneous calculation of the complicated fracture of several fault segments and the subsurface propagation of seismic waves, we gained exciting insights into the geophysical processes of the earthquake.”
In particular, says Dr.Gabriel, “The splay faults, which can be imagined as pop-up fractures alongside the known subduction trench, led to abrupt, long-period, vertical displacements of the seafloor, and thus to an increased tsunami risk. At present, this capability of incorporating such realistic geometries into physical earthquake models is unique worldwide.”
Glacial polish reflects sunlight at Pothole Dome in Yosemite National Park, California. The granitic bedrock here was polished by glacier sliding during the Last Glacial Maximum. UCSC researchers found that glacial polish forms by the accretion of a thin coating layer on top of glacially abraded surfaces. Credit: Shalev Siman-Tov
The glaciers that carved Yosemite Valley left highly polished surfaces on many of the region’s rock formations. These smooth, shiny surfaces, known as glacial polish, are common in the Sierra Nevada and other glaciated landscapes.
Geologists at UC Santa Cruz have now taken a close look at the structure and chemistry of glacial polish and found that it consists of a thin coating smeared onto the rock as the glacier moved over it. The new findings, published in the November issue of Geology, show that the polish is not simply the result of abrasion and smoothing by the glacier, as was previously thought. Instead, it is a distinct layer deposited onto the surface of the rock at the base of the glacier.
This smooth layer coating the rock at the base of glaciers may influence how fast the glaciers slide. It also helps explain why glacial polish is so resistant to weathering long after the glaciers that created it are gone.
According to coauthor Emily Brodsky, professor of Earth and planetary sciences at UC Santa Cruz, this ultrathin coating can help glaciologists better understand the mechanics of how glaciers move, and it provides a potential archive for dating when the material was pasted onto the rock.
“This is incredibly important now, as we think about the stability of ice sheets,” Brodsky said. “It is pretty hard to get to the base of a glacier to see what’s going on there, but the glacial polish can tell us about the composition of the gunk on the bottoms of glaciers and when the polish was formed.”
Lead author Shalev Siman-Tov, a postdoctoral researcher at UC Santa Cruz, had previously studied the highly polished surfaces found on some earthquake faults. To investigate glacial polish, he teamed up with Greg Stock, who earned his Ph.D. at UC Santa Cruz and is now the park geologist at Yosemite National Park.
“I wanted to apply what we know from fault zones and earthquakes to glaciology,” Siman-Tov said. “I was not familiar with glaciated landscapes, and I was very interested to conduct a significant field study outside of my home country of Israel.”
He and Stock hiked into Yosemite National Park to collect small samples of glacial polish from dozens of sites. They chose samples from three sites for detailed analyses. One site (Daff Dome near Tuolomne Meadows) emerged from beneath the glaciers at the end of the last ice age around 15,000 years ago. The other two sites are in Lyell Canyon near small modern glaciers that formed during the Little Ice Age around 300 years ago. Lyell Glacier is no longer active, but McClure Glacier is still moving and has an ice cave at its toe that enabled the researchers to collect fresh polish from an area of active sliding and abrasion.
The researchers used an ion beam to slice off thin sections from the samples, and they used electron microscopy techniques to image the samples and perform elemental analyses. The results showed that the tiny fragments in the coating were a mixture of all the minerals found in granodiorite bedrock. This suggests a process in which the glacier scrapes material from the rocks and grinds it into a fine paste, then spreads it across the rock surface to form a very thin layer only a few microns thick.
“Abrasive wear removes material and makes the surface smoother, while simultaneously producing the wear products that become the construction material for the coating layer,” the researchers wrote in the paper.
Siman-Tov now wants to date the layer and confirm the time when the glacier eroded the rock surface. He is also conducting laboratory experiments to try to recreate the same structures observed in the coating layer. The researchers will continue to work with Stock in Yosemite to study the chemical weathering of glacial polish surfaces compared to regular, exposed granodiorite.
Reference:
Shalev Siman-Tov et al, The coating layer of glacial polish, Geology (2017). DOI: 10.1130/G39281.1
