Tagged: Geophysics Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 3:56 pm on March 5, 2019 Permalink | Reply
    Tags: , , Earthquake hazards, Geophysicists at Caltech have created a new method for determining earthquake hazards by measuring how fast energy is building up on faults in a specific region and then comparing that to how much is , Geophysics, , , The method also allows for an assessment of the likelihood of smaller earthquakes. If one excludes aftershocks the probability that a magnitude 6.0 or greater earthquake will occur in central LA over , They applied the new method to the faults underneath central Los Angeles and found that on the long-term average the strongest earthquake that is likely to occur along those faults is between magnitud, They find that the crust beneath Los Angeles does not seem to be being squeezed from south to north fast enough to make such an earthquake quite as likely, When one tectonic plate pushes against another elastic strain is built up along the boundary between the two plates. The strain increases until one plate either creeps slowly past the other or it jerk   

    From Caltech: “Fast, Simple New Assessment of Earthquake Hazard” 

    Caltech Logo

    From Caltech

    1
    Credit: Juan Vargas, Jean-Philippe Avouac, Chris Rollins / Caltech

    March 04, 2019

    Contact
    Robert Perkins
    (626) 395‑1862
    rperkins@caltech.edu

    Geophysicists at Caltech have created a new method for determining earthquake hazards by measuring how fast energy is building up on faults in a specific region, and then comparing that to how much is being released through fault creep and earthquakes.

    They applied the new method to the faults underneath central Los Angeles, and found that on the long-term average, the strongest earthquake that is likely to occur along those faults is between magnitude 6.8 and 7.1, and that a magnitude 6.8—about 50 percent stronger than the 1994 Northridge earthquake—could occur roughly every 300 years on average.

    That is not to say that a larger earthquake beneath central L.A. is impossible, the researchers say; rather, they find that the crust beneath Los Angeles does not seem to be being squeezed from south to north fast enough to make such an earthquake quite as likely.

    The method also allows for an assessment of the likelihood of smaller earthquakes. If one excludes aftershocks, the probability that a magnitude 6.0 or greater earthquake will occur in central LA over any given 10-year period is about 9 percent, while the chance of a magnitude 6.5 or greater earthquake is about 2 percent.

    A paper describing these findings was published by Geophysical Research Letters on February 27.

    These levels of seismic hazard are somewhat lower but do not differ significantly from what has already been predicted by the Working Group on California Earthquake Probabilities. But that is actually the point, the Caltech scientists say.

    Current state-of-the-art methods for assessing the seismic hazard of an area involve generating a detailed assessment of the kinds of earthquake ruptures that can be expected along each fault, a complicated process that relies on supercomputers to generate a final model. By contrast, the new method—developed by Caltech graduate student Chris Rollins and Jean-Philippe Avouac, Earle C. Anthony Professor of Geology and Mechanical and Civil Engineering—is much simpler, relying on the strain budget and the overall earthquake statistics in a region.

    “We basically ask, ‘Given that central L.A. is being squeezed from north to south at a few millimeters per year, what can we say about how often earthquakes of various magnitudes might occur in the area, and how large earthquakes might get?'” Rollins says.

    When one tectonic plate pushes against another, elastic strain is built up along the boundary between the two plates. The strain increases until one plate either creeps slowly past the other, or it jerks violently. The violent jerks are felt as earthquakes.

    Fortunately, the gradual bending of the crust between earthquakes can be measured at the surface by studying how the earth’s surface deforms. In a previous study [JGR Solid Earth] (done in collaboration with Caltech research software engineer Walter Landry; Don Argus of the Jet Propulsion Laboratory, which is managed by Caltech for NASA; and Sylvain Barbot of USC), Avouac and Rollins measured ground displacement using permanent global positioning system (GPS) stations that are part of the Plate Boundary Observatory network, supported by the National Science Foundation (NSF) and NASA. The GPS measurements revealed how fast the land beneath L.A. is being bent. From that, the researchers calculated how much strain was being released by creep and how much was being stored as elastic strain available to drive earthquakes.

    This research was supported by a NASA Earth and Space Science Fellowship.

    See the full article here .

    Earthquake Alert

    1

    Earthquake Alert

    Earthquake Network projectEarthquake Network is a research project which aims at developing and maintaining a crowdsourced smartphone-based earthquake warning system at a global level. Smartphones made available by the population are used to detect the earthquake waves using the on-board accelerometers. When an earthquake is detected, an earthquake warning is issued in order to alert the population not yet reached by the damaging waves of the earthquake.

    The project started on January 1, 2013 with the release of the homonymous Android application Earthquake Network. The author of the research project and developer of the smartphone application is Francesco Finazzi of the University of Bergamo, Italy.

    Get the app in the Google Play store.

    3
    Smartphone network spatial distribution (green and red dots) on December 4, 2015

    Meet The Quake-Catcher Network

    QCN bloc

    Quake-Catcher Network

    The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.

    After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).

    The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).

    The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).

    There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.

    Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.

    USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.

    If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.

    BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.

    Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.

    Below, the QCN Quake Catcher Network map
    QCN Quake Catcher Network map

    ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States

    The U. S. Geological Survey (USGS) along with a coalition of State and university partners is developing and testing an earthquake early warning (EEW) system called ShakeAlert for the west coast of the United States. Long term funding must be secured before the system can begin sending general public notifications, however, some limited pilot projects are active and more are being developed. The USGS has set the goal of beginning limited public notifications in 2018.

    Watch a video describing how ShakeAlert works in English or Spanish.

    The primary project partners include:

    United States Geological Survey
    California Governor’s Office of Emergency Services (CalOES)
    California Geological Survey
    California Institute of Technology
    University of California Berkeley
    University of Washington
    University of Oregon
    Gordon and Betty Moore Foundation

    The Earthquake Threat

    Earthquakes pose a national challenge because more than 143 million Americans live in areas of significant seismic risk across 39 states. Most of our Nation’s earthquake risk is concentrated on the West Coast of the United States. The Federal Emergency Management Agency (FEMA) has estimated the average annualized loss from earthquakes, nationwide, to be $5.3 billion, with 77 percent of that figure ($4.1 billion) coming from California, Washington, and Oregon, and 66 percent ($3.5 billion) from California alone. In the next 30 years, California has a 99.7 percent chance of a magnitude 6.7 or larger earthquake and the Pacific Northwest has a 10 percent chance of a magnitude 8 to 9 megathrust earthquake on the Cascadia subduction zone.

    Part of the Solution

    Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of the ShakeAlert system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage.

    Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds. ShakeAlert can give enough time to slow trains and taxiing planes, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or chemicals in work environments and to take cover under a desk, or to automatically shut down and isolate industrial systems. Taking such actions before shaking starts can reduce damage and casualties during an earthquake. It can also prevent cascading failures in the aftermath of an event. For example, isolating utilities before shaking starts can reduce the number of fire initiations.

    System Goal

    The USGS will issue public warnings of potentially damaging earthquakes and provide warning parameter data to government agencies and private users on a region-by-region basis, as soon as the ShakeAlert system, its products, and its parametric data meet minimum quality and reliability standards in those geographic regions. The USGS has set the goal of beginning limited public notifications in 2018. Product availability will expand geographically via ANSS regional seismic networks, such that ShakeAlert products and warnings become available for all regions with dense seismic instrumentation.

    Current Status

    The West Coast ShakeAlert system is being developed by expanding and upgrading the infrastructure of regional seismic networks that are part of the Advanced National Seismic System (ANSS); the California Integrated Seismic Network (CISN) is made up of the Southern California Seismic Network, SCSN) and the Northern California Seismic System, NCSS and the Pacific Northwest Seismic Network (PNSN). This enables the USGS and ANSS to leverage their substantial investment in sensor networks, data telemetry systems, data processing centers, and software for earthquake monitoring activities residing in these network centers. The ShakeAlert system has been sending live alerts to “beta” users in California since January of 2012 and in the Pacific Northwest since February of 2015.

    In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert early warning test system in California joined by Oregon and Washington in April 2017. This West Coast-wide “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost.

    This next-generation system will not yet support public warnings but does allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert notifications in areas with sufficient sensor coverage.

    Authorities

    The USGS will develop and operate the ShakeAlert system, and issue public notifications under collaborative authorities with FEMA, as part of the National Earthquake Hazard Reduction Program, as enacted by the Earthquake Hazards Reduction Act of 1977, 42 U.S.C. §§ 7704 SEC. 2.

    For More Information

    Robert de Groot, ShakeAlert National Coordinator for Communication, Education, and Outreach
    rdegroot@usgs.gov
    626-583-7225

    Learn more about EEW Research

    ShakeAlert Fact Sheet

    ShakeAlert Implementation Plan


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus


    Caltech campus

     
  • richardmitnick 1:22 pm on March 9, 2018 Permalink | Reply
    Tags: , Diamonds with ice VII, , , Geophysics, ice VII, Pockets of water may lay deep below Earth’s surface,   

    From Science: “Pockets of water may lay deep below Earth’s surface” 

    AAAS
    Science Magazine

    Mar. 8, 2018
    Sid Perkins

    1
    New evidence of water pockets has been found hundreds of kilometers deep inside our planet. Claus Lunau/Science Source.

    Small pockets of water exist deep beneath Earth’s surface, according to an analysis of diamonds belched from hundreds of kilometers within our planet. The work, which also identifies a weird form of crystallized water known as ice VII, suggests that material may circulate more freely at some depths within Earth than previously thought. Geophysical models of that flow, which ultimately influences the frequency of earthquakes driven by the scraping of tectonic plates at Earth’s surface, may need to be substantially tweaked, scientists say. Such models also help scientists estimate the long-term rates of heat flow through Earth’s surface and into space.

    “These diamonds seem to be returning confirmation, and a few new surprises, of what’s happening deep within Earth,” says Steven Shirey, a geochemist at the Carnegie Institution for Science in Washington, D.C., who was not involved in the study. One of the biggest surprises, he suggests, is evidence for the presence of unbound water at depths below 600 kilometers.

    Pure diamonds are made of nothing but carbon, but most contain small impurities that take the form of tiny crystals. These inclusions offer clues about how and where the gems formed, says Oliver Tschauner, a mineralogist at University of Nevada in Las Vegas. In a 2016 study, for example, metal-rich inclusions found in dozens of large, clear diamonds suggested that those gemstones formed in pockets of liquid metal.

    Recently, Tschauner and his colleagues analyzed diamonds unearthed at several sites in southern Africa and China. More than a dozen of them contained a new type of inclusion—a distinct form of crystallized water known as ice VII. (Scientists have discovered more than a dozen types of ice crystals, including ice IX—which, unlike Kurt Vonnegut’s fictional ice-nine, doesn’t freeze up the world’s oceans.) Ice VII is well known from lab studies of materials under high pressure, Tschauner says, but the samples he and his colleagues describe are the first known natural samples, the researchers report today in Science. Based on the team’s data, ice VII has been declared a new mineral.

    2
    X-rays scattered from water trapped in a diamond (light gray pixels seen near arrow) suggest that watery fluids can be found deep inside Earth.
    Tschauner Et al./Science (2018)

    The identification of ice inside those diamonds provides scientists with more than a nifty new mineral, Tschauner says. It also suggests that pockets of watery fluids exist at great depths in Earth’s mantle [Science]. This water, rather than being chemically bound in rocks in combinations called hydrated minerals, is free-floating and remains a liquid—despite the high temperatures found in the mantle, the layer sandwiched between Earth’s crust and core. The team’s analyses suggest that some of the diamonds they studied formed at depths between 610 and 800 kilometers below Earth’s surface—the first direct evidence of unbonded water at such extreme depths, Tschauner notes. Nevertheless, the new research doesn’t help pin down how large those pockets are or how common they may be.

    Alongside the ice VII inclusions were tiny crystals of calcite and various types of salts, Tschauner says. Thus, he and his colleagues contend that the diamonds they analyzed crystallized in pockets of watery, salty fluid at depths well below the level at which scientists had previously identified water unbound to other minerals.

    The presence of watery fluids at or below the boundary between the upper and lower mantle could definitely affect how and where heat is generated in the mantle, says Oded Navon, a mantle geochemist at The Hebrew University of Jerusalem. For instance, such watery fluids could more readily carry certain forms of easily dissolved radioactive elements from one part of the mantle to another. That could affect where in the mantle heat-generating radioactive decay occurs, which, in turn, could make the heated areas less viscous and thus prone to flow more readily. All these changes could influence the rates, over the long term, at which heat escapes from Earth’s interior.

    Among other things, the varying composition of materials at different layers of the mantle can affect where and how well tectonic slabs that have sunk back into Earth’s interior melt and release their minerals, Tschauner and his team contend. For instance, the density and viscosity of Earth’s interior affect the level at which sinking slabs reach neutral buoyancy, thus stalling their descent. That, in turn, influences where the slabs melt and release the water and other minerals they hold. Overall, the team’s new findings may lead to more accurate models of what’s going on at different depths deep within Earth.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 1:03 pm on August 18, 2017 Permalink | Reply
    Tags: , Geophysics, Hot spot at Hawaii? Not so fast, Hot spots around the globe can be used to determine how fast tectonic plates move, , Paleogeography, , Seamounts, The Pacific Plate moves relative to the hot spots at about 100 millimeters per year   

    From Rice: “Hot spot at Hawaii? Not so fast” 

    Rice U bloc

    Rice University

    August 18, 2017
    Mike Williams

    Rice University scientists’ model shows global mantle plumes don’t move as quickly as thought

    Through analysis of volcanic tracks, Rice University geophysicists have concluded that hot spots like those that formed the Hawaiian Islands aren’t moving as fast as recently thought.

    Hot spots are areas where magma pushes up from deep Earth to form volcanoes. New results from geophysicist Richard Gordon and his team confirm that groups of hot spots around the globe can be used to determine how fast tectonic plates move.

    1
    Rice University geophysicists have developed a method that uses the average motion of hot-spot groups by plate to determine that the spots aren’t moving as fast as geologists thought. For example, the Juan Fernandez Chain (outlined by the white rectangle) on the Nazca Plate west of Chile was formed by a hot spot now at the western end of the chain as the Nazca moved east-northeast relative to the hotspot forming the chain that includes Alejandro Selkirk and Robinson Crusoe islands. The white arrow shows the direction of motion of the Nazca Plate relative to the hot spot, and it is nearly indistinguishable from the direction predicted from global plate motions relative to all the hot spots on the planet (green arrow). The similarity in direction indicates that very little motion of the Juan Fernandez hot spot relative to other hot spots is needed to explain its trend. Illustration by Chengzu Wang.

    Gordon, lead author Chengzu Wang and co-author Tuo Zhang developed a method to analyze the relative motion of 56 hot spots grouped by tectonic plates. They concluded that the hot-spot groups move slowly enough to be used as a global reference frame for how plates move relative to the deep mantle. This confirmed the method is useful for viewing not only current plate motion but also plate motion in the geologic past.

    The study appears in Geophysical Research Letters.

    Hot spots offer a window into the depths of Earth, as they mark the tops of mantle plumes that carry hot, buoyant rock from deep Earth to near the surface and produce volcanoes. These mantle plumes were once thought to be straight and stationary, but recent results suggested they can also shift laterally in the convective mantle over geological time.

    The primary evidence of plate movement relative to the deep mantle comes from volcanic activity that forms mountains on land, islands in the ocean or seamounts, mountain-like features on the ocean floor. A volcano forms on a tectonic plate above a mantle plume. As the plate moves, the plume gives birth to a series of volcanoes. One such series is the Hawaiian Islands and the Emperor Seamount Chain; the youngest volcanoes become islands while the older ones submerge. The series stretches for thousands of miles and was formed as the Pacific Plate moved over a mantle plume for 80 million years.

    The Rice researchers compared the observed hot-spot tracks with their calculated global hot-spot trends and determined the motions of hot spots that would account for the differences they saw. Their method demonstrated that most hot-spot groups appear to be fixed and the remainder appear to move slower than expected.

    “Averaging the motions of hot-spot groups for individual plates avoids misfits in data due to noise,” Gordon said. “The results allowed us to say that these hot-spot groups, relative to other hot-spot groups, are moving at about 4 millimeters or less a year.

    “We used a method of analysis that’s new for hot-spot tracks,” he said. “Fortunately, we now have a data set of hot-spot tracks that is large enough for us to apply it.”

    For seven of the 10 plates they analyzed with the new method, average hot-spot motion measured was essentially zero, which countered findings from other studies that spots move as much as 33 millimeters a year. Top speed for the remaining hot-spot groups — those beneath the Eurasia, Nubia and North America plates — was between 4 and 6 millimeters a year but could be as small as 1 millimeter per year. That’s much slower than most plates move relative to the hot spots. For example, the Pacific Plate moves relative to the hot spots at about 100 millimeters per year.

    Gordon said those interested in paleogeography should be able to make use of the model. “If hot spots don’t move much, they can use them to study prehistorical geography. People who are interested in circum-Pacific tectonics, like how western North America was assembled, need to know that history of plate motion.

    “Others who will be interested are geodynamicists,” he said. “The motions of hot spots reflect the behavior of mantle. If the hot spots move slowly, it may indicate that the viscosity of mantle is higher than models that predict fast movement.”

    “Modelers, especially those who study mantle convection, need to have something on the surface of Earth to constrain their models, or to check if their models are correct,” Wang said. “Then they can use their models to predict something. Hot-spot motion is one of the things that can be used to test their models.”

    Gordon is the W.M. Keck Professor of Earth Science. Wang and Zhang are Rice graduate students. The National Science Foundation supported the research.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Rice U campus

    In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

    This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

     
  • richardmitnick 12:38 pm on August 1, 2016 Permalink | Reply
    Tags: , , , Geophysics,   

    From Eos: “Mapping the Movement of Energy Under Japan” 

    Eos news bloc

    Eos

    8.1.16
    Leah Crane

    New research on the energy waves caused by earthquakes provides the most detailed map to date of the subduction zone beneath Japan.

    1
    The Japan islands, pictured here, sit atop four lithospheric plates. The movement and interaction of those plates subject Japan to earthquakes, tsunamis, and volcanic eruptions. Credit: NASA/GSFC/Aqua

    Deep under the islands of Japan, the crust and mantle of the Earth move and crack. Four lithospheric plates—the Eurasian, Okhotsk, Pacific, and Philippine Sea plates—crunch together there. The strong interactions at the interface of those plates make the Japan subduction zone a prime location for active volcanoes, tsunamis, and earthquakes.

    As earthquakes and other seismic events occur, they send waves of energy rumbling through the Earth. In studying how those waves move in three dimensions, Liu and Zhao developed an increased understanding of how the lithospheric plates interact with the area around them and react to the energy pulsing through them.

    Seismic events like earthquakes release energy through the Earth. As the waves propagate through varying materials, they can reveal the seismic anisotropy, or how the velocity of energy traveling through the Earth is affected by the direction or angle of propagation. When there are vertical cracks in the Earth—as is particularly common in subduction zones where the crust and mantle are most stressed—it causes azimuthal anisotropy, which means that the horizontal direction of wave propagation has a greater effect on variations in velocity.

    The researchers used the Kiban network of 1852 seismic stations to record the travel times of seismic waves from 2528 earthquakes in and around the Japan Islands. They also recorded seismic wave travel times from 747 other teleseismic events, or earthquakes that originated more than 3000 kilometers from the station sites. From these two data sets, the authors were able to recreate the motion of the waves, building a high-resolution three-dimensional map of the azimuthal anisotropy structure of the Japan subduction zone down to an unprecedented depth of 700 kilometers.

    The study found that energy waves traveled faster parallel to trenches along the subducting Pacific and Philippine Sea plates, perhaps because of the orientation of certain minerals or faults on the ocean floor. However, things get more complicated in Earth’s mantle: Plate subduction and dehydration joined with convective circulation to cause energy to flow perpendicularly to the trenches and even in a toroidal pattern around a hole in the Philippine Sea plate. Unexplained anomalies remain, particularly under the Pacific slab beneath northeast Japan, but this study has provided a more detailed description of the Japan subduction zone than any previous research. (Journal of Geophysical Research: Solid Earth, doi:10.1002/2016JB013116, 2016)

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 8:27 am on April 2, 2016 Permalink | Reply
    Tags: , Geologists To Drill Into Heart of Dinosaur-Killing Impact, Geophysics,   

    From SA: “Geologists To Drill Into Heart of Dinosaur-Killing Impact” 

    Scientific American

    Scientific American

    April 1, 2016
    Alexandra Witze

    1
    The asteroid that created Chicxulub crater reshaped life on Earth. Science Photo Library via Getty Images

    2
    http://www.meteoritecollector.org/

    Geophysicists are returning to Earth’s most famous cosmic bullseye. Around April 7, from a drill-ship off the coast of Yucatán, Mexico, they will start to penetrate the 200-kilometre-wide Chicxulub crater, which formed 66 million years ago when an enormous asteroid smashed into the planet. The aftermath of the impact obliterated most life on Earth, including the dinosaurs.

    The expedition is the first to directly probe one of Chicxulub’s most striking features—its ‘peak ring’, a circle of mountains that rises within the crater floor. Scientists have yet to fully explain how peak rings form, even though they are common in big impact craters across the Solar System.

    3
    An illustration of the Chicxulub impact crater in the Yucatán Peninsula. Illustration by Detlev van Ravenswaay, Science Source

    At Chicxulub, researchers will look for evidence to explain how a 14-kilometre-wide asteroid could have punched a hole that pushed rocks from the surface down some 20–30 kilometres. Flowing like liquid, the rocks then rebounded towards the sky—reaching as far as 10 kilometres above the original ground level—and finally splattered down to form a peak ring.

    All of this happened in the span of several devastating minutes, says Joanna Morgan, a geophysicist at Imperial College London and the project’s co-chief scientist. “It’s astounding.”

    If the 2-month expedition goes as planned, it will bore 1,500 metres into sea-floor rocks. The drill will first pass through carbonate rocks that make up the bottom of the Gulf of Mexico (see map), and eventually reach the fractured ‘impact breccias’ that represent the obliterating impact.

    At least a dozen other boreholes and several oil-exploration wells have already penetrated the parts of Chicxulub that lie on land. They include a 1,511-metre-long core drilled near the crater rim in 2001–02 by a large international scientific consortium. When combined with seismic surveys, analyses of existing cores reveal a complex picture of nested rings of shattered rock, all created on a very bad day for life on Earth.

    Inner circle

    The latest project will be the first to drill offshore at Chicxulub, and the first to target its peak ring. “We don’t really know what this material will look like,” says Jaime Urrutia-Fucugauchi, a geophysicist at the National Autonomous University of Mexico in Mexico City. “It could be a real surprise.”

    The US$10-million project is funded primarily by the European Consortium for Ocean Research Drilling, and involves researchers from Europe, Mexico, the United States and elsewhere. The water at the drill site—about 30 kilometres offshore from the port of Progreso—is too shallow to accommodate conventional ocean-drilling vessels, so the project has hired LB Myrtle, a ‘lift boat’ that will drop three enormous pillars to the sea floor, then jack itself up to form a temporary drilling platform.

    Chicxulub is the only impact crater on Earth both big enough and well-preserved enough to still have a peak ring. Finding out exactly how the rocks are layered in the core will help researchers to evaluate several competing models of peak-ring formation, says David Kring, a geologist at the Lunar and Planetary Institute in Houston, Texas. He and his colleagues studied the peak ring inside the lunar crater Schrödinger to predict what sorts of rock might exist in the Chicxulub core.

    Drillers will quickly bore their way through the top 500 metres of sediments, and then collect core samples more carefully as they go deeper. “At every level you’ll get a win,” says Sean Gulick, a geophysicist at the University of Texas at Austin and the expedition’s other co-chief scientist. At about 600 metres, the core will pass through rock from the Palaeocene–Eocene Thermal Maximum, when temperatures spiked about 55 million years ago, creating a greenhouse world. At 650 metres the core should hit the peak ring.
    Primordial ooze

    Perhaps the biggest question about the peak ring is where its rocks came from. If the rocks within the ring are relatively light in colour, they probably came from the topmost 5–10 kilometres of Earth’s crust. Darker rocks are likely to be rich in elements such as iron and magnesium, and probably came from greater depths—perhaps 10–15 kilometres down. Confirming the depth of the peak-ring rocks will help modellers to understand how the crust fractures and flows during a giant impact.

    The core could also reveal whether the impact fostered life even while destroying it. When the asteroid shattered Earth’s crust, heat and water began flowing through the fragmented rocks. Microbes may have thrived in that warm, watery habitat, so microbiologists will test the cores for ancient DNA and other signatures of living organisms. “By looking directly at ground zero, we can watch life recover,” says Gulick.

    From the drill rig, the cores will be sent to Bremen, Germany, for more detailed study later this year. Urrutia-Fucugauchi hopes that some of the most dramatic samples will eventually return to Mexico, perhaps to a new core laboratory at the Yucatán Science and Technology Park on the outskirts of Mérida.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 4:21 pm on December 18, 2015 Permalink | Reply
    Tags: , , Geophysics,   

    From SA: “Magnetic Mystery of Earth’s Early Core Explained” 

    Scientific American

    Scientific American

    December 18, 2015
    Alexandra Witze

    1
    Yuri_Arcurs ©iStock.com

    Geophysicists call it the new core paradox: They can’t quite explain how the ancient Earth could have sustained a magnetic field billions of years ago, as it was cooling from its fiery birth.

    Now, two scientists have proposed two different ways to solve the paradox. Each relies on minerals crystallizing out of the molten Earth, a process that would have generated a magnetic field by churning the young planet’s core. The difference between the two explanations comes in which particular mineral does the crystallizing.

    Silicon dioxide is the choice of Kei Hirose, a geophysicist at the Tokyo Institute of Technology who runs high-pressure experiments to simulate conditions deep within the Earth. “I’m very confident in this,” he reported on December 17 at a meeting of the American Geophysical Union in San Francisco, California.

    But David Stevenson, a geophysicist at the California Institute of Technology in Pasadena, says that magnesium oxide — not silicon dioxide—is the key to solving the problem. In unpublished work, Stevenson proposes that magnesium oxide, settling out of the molten early Earth, could have set up the buoyancy differences that would drive an ancient geodynamo.

    The core paradox arose in 2012, when several research teams reported that Earth’s core loses heat at a faster rate than once thought. More heat conducting away from the core means less heat available to churn the core’s liquid. That’s important because some studies suggest Earth could have had a magnetic field more than 4 billion years ago—just half a billion years after it coalesced from fiery debris swirling around the newborn Sun. “We need a dynamo more or less continuously,” Peter Driscoll, a geophysicist at the Carnegie Institution for Science in Washington DC, said at the meeting.

    In his Tokyo laboratory, Hirose put different combinations of iron, silicon and oxygen into a diamond anvil cell and squeezed them to produce extraordinarily high pressures and temperatures—sometimes above 4,000 ºC—to simulate the hellish conditions of Earth’s interior. He found that silicon and oxygen crystallized out together, as silicon dioxide, whenever both were present.

    When silicon dioxide precipitated in the early Earth, it would have made the remaining melt buoyant enough to continue rising, thus setting up the churning motion needed to sustain the dynamo, Hirose reported. “As far as I know, this is the most feasible mechanism to drive the geodynamo,” he said.

    Stevenson, in contrast, plumps for magnesium, saying it “makes much more sense” than silicon dioxide because magnesium oxide would precipitate out of a molten Earth first. Hirose, he says, “is telling you something that can happen, not what did happen.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: