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Geoscientists Use Numerical Model to Understand Forces Behind Earthquakes

Researchers used their model to help explain the stresses that act on Earth's tectonic plates. Those stresses result in earthquakes not only at the boundaries between tectonic plates, where most earthquakes occur, but also in the plate interiors, where the forces are less understood. (Credit: © Anton Balazh / Fotolia)

Stony Brook University researchers have devised a numerical model to help explain the linkage between earthquakes and the powerful forces that cause them, according to a research paper scheduled to be published in the journal Science on Feb. 17. Their findings hold implications for long-term forecasting of earthquakes.

William E. Holt, Ph.D., a professor in the Geosciences Department at Stony Brook University, and Attreyee Ghosh, Ph.D., a post doctoral associate, used their model to help explain the stresses that act on Earth’s tectonic plates. Those stresses result in earthquakes not only at the boundaries between tectonic plates, where most earthquakes occur, but also in the plate interiors, where the forces are less understood, according to their paper, “Plate Motions and Stresses from Global Dynamic Models.”

“If you take into account the effects of topography and all density variations within the plates — the Earth’s crust varies in thickness depending on where you are — if you take all that into account, together with the mantle convection system, you can do a good job explaining what is going on at the surface,” said Dr. Holt.

Their research focused on the system of plates that float on Earth’s fluid-like mantle, which acts as a convection system on geologic time scales, carrying them and the continents that rest upon them. These plates bump and grind past one another, diverge from one another, or collide or sink (subduct) along the plate boundary zones of the world. Collisions between the continents have produced spectacular mountain ranges and powerful earthquakes. But the constant stress to which the plates are subjected also results in earthquakes within the interior of those plates.

“Predicting plate motions correctly, along with stresses within the plates, has been a challenge for global dynamic models,” the researchers wrote. “Accurate predictions of these is vitally important for understanding the forces responsible for the movement of plates, mountain building, rifting of continents, and strain accumulation released in earthquakes.”

Data for their global computer model came from Global Positioning System (GPS) measurements, which track the movements of Earth’s crust within the deforming plate boundary zones; measurements on the orientation of Earth’s stress field gleaned from earthquake faults; and a network of global seismometers that provided a picture of Earth’s interior density variations. They compared output from their model with these measurements from Earth’s surface.

“These observations — GPS, faults — allow one to test the completeness of the model,” Dr. Holt said.

Drs. Ghosh and Holt found that plate tectonics is an integrated system, driven by density variations found between the surface of Earth all the way to Earth’s core-mantle boundary. A surprising find was the variation in influence between relatively shallow features (topography and crustal thickness variations) and deeper large-scale mantle flow patterns that assist and, in some places, resist plate motions. Ghosh and Holt also found that it is the large-scale mantle flow patterns, set up by the long history of sinking plates, that are important for influencing the stresses within, and motions of, the plates.

Topography also has a major influence on the plate tectonic system, the researchers found. That result suggests a powerful feedback between the forces that make the topography and the ‘push-back’ on the system exerted by the topography, they explained.

While their model cannot accurately predict when and where earthquakes will occur in the short-term, “it can help at better understanding or forecasting earthquakes over longer time spans,” Dr. Holt said. “Nobody can yet predict, but ultimately given a better understanding of the forces within the system, one can develop better forecast models.”

…(Science Daily)

February 27, 2012 Posted by | Science, Seismic | , , , , , | Leave a comment

Volcanologists Monitor Swarm of New Tremors at El Hierro

The submarine eruption south of El Hierro Island could be in a process of change: While visible activity on the sea surface above the vent, as well as harmonic tremor signal (thought to be more or less proportional to erupting magma flux) have nearly ceased, the number of earthquakes under the island has increased sharply since yesterday.

On 15 February, more than 20 quakes were measured. Most of the earthquakes were very small, well below magnitude 2, and were clustered beneath the NW and SW sectors of the island at depths of around 10 km. There is no conclusive interpretation of this measurement.

A possible (and usually assumed) scenario is that rising new magma from the mantle reservoir is creating new intrusions and rupturing rock to create pathways in the crust under El Hierro, not using the same paths as until now. That would explain why less magma is currently being erupted at the current vent(s). In that scenario, the eruption will continue, perhaps even from a different vent, and an increase in magma output is going to be expected any time soon. However, this is speculation.

The earthquakes could as well be related to some other (known or unknown) process, e.g. gravity-induced adjustments that respond to pressure changes and occur within previously ruptured areas of the crust beneath the island.

The next days or weeks will show what happens next.

…(Volcano Discovery)

February 17, 2012 Posted by | Science, Volcanic | , , , , , , | 1 Comment

How an Earthquake Warps a Landscape

A team of geologists from the U.S., Mexico and China are using light detection and ranging (LiDAR) laser altimetry to study how an earthquake can change a landscape. In particular, the geologists want to know more about the magnitude 7.2 quake that struck April 4, 2010, near Mexicali in northern Mexico. Airborne LiDAR equipment, which bounces a stream of laser pulses off the ground, can measure surface features to within a few centimeters. The researchers were able to make a detailed scan of the affected area over about 360 square kilometers in less than three days, they report in the February 10 issue of the journal Science.

In the above image, blue shows where ground surface moved down whereas red indicates upward movement compared with the previous survey.

LiDAR has a number of applications. Researchers have used it to study the properties of Saharan dust clouds for climate models as well as to gather detailed information on the plume emanating from Iceland’s Eyjafjallajökull volcano. Mexico had used LiDAR to map the Mexicali region in 2006, so Michael Oskin, a geology professor at the University of California, Davis, the paper’s lead author, and his colleagues had a baseline with which to compare their results.

Some changes brought about by the quake are readily visible from the ground, such as a 1.5-meter clifflike ridge created when part of a hillside abruptly moved up and sideways. But the LiDAR survey also revealed some features that could not easily be detected otherwise, Oskin reports, such as a warping of the ground surface above the Indiviso Fault, which runs beneath agricultural fields along the Colorado River floodplain.

The 2010 Mexicali earthquake did not occur on a major fault, such as the San Andreas, but rather ran through a series of smaller fractures in Earth’s crust. The new LiDAR survey shows how seven of these small faults came together to cause a major quake.

…(Scientific American)

February 11, 2012 Posted by | Science, Seismic | , , , , , , , , , , , , | Leave a comment

Solar Activity Picks Up, Mars Approach Nears

NORTHEASTERN ERUPTION: Solar activity is picking up. During the late hours of Feb. 9th, a dark magnetic filament winding over the sun’s northeastern limb rose up and exploded. NASA’s Solar Dynamics Observatory recorded the action:

The eruption hurled a bright coronal mass ejection (CME) away from the sun: SOHO movie

The expanding cloud is not heading for Earth, but in a day or so it might make contact with Venus, which appears to be in the line of fire.

The emergence of a new sunspot at the root of the erupting filament plus the rapid growth of existing sunspot AR1416 could foreshadow more activity in the days ahead.

MOON-MARS: Mars is approaching Earth for a close encounter in early March. Already the Red Planet is five times brighter than a 1st-magnitude star. Solar flare alerts: textvoice.

February 10, 2012 Posted by | Science, Solar, Space | , , , , , , | 1 Comment

Surface of Mars an Unlikely Place for Life After 600-Million Year Drought, Says Scientists

Mars may have been arid for more than 600 million years, making it too hostile for any life to survive on the planet’s surface, according to researchers who have been carrying out the painstaking task of analysing individual particles of Martian soil. Dr Tom Pike, from Imperial College London, will discuss the team’s analysis at a European Space Agency (ESA) meeting on 7 February 2012.

The researchers have spent three years analysing data on Martian soil that was collected during the 2008 NASA Phoenix mission to Mars. Phoenix touched down in the northern arctic region of the planet to search for signs that it was habitable and to analyse ice and soil on the surface.

The results of the soil analysis at the Phoenix site suggest the surface of Mars has been arid for hundreds of millions of years, despite the presence of ice and the fact that previous research has shown that Mars may have had a warmer and wetter period in its earlier history more than three billion years ago. The team also estimated that the soil on Mars had been exposed to liquid water for at most 5,000 years since its formation billions of years ago. They also found that Martian and Moon soil is being formed under the same extremely dry conditions.

Satellite images and previous studies have proven that the soil on Mars is uniform across the planet, which suggests that the results from the team’s analysis could be applied to all of Mars. This implies that liquid water has been on the surface of Mars for far too short a time for life to maintain a foothold on the surface.

“We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years. We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life. Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.”

During the Phoenix mission, Dr Pike and his research group formed one of 24 teams based at mission control in the University of Arizona in the USA, operating part of the spacecraft’s onboard laboratories. They analysed soil samples dug up by a robot arm, using an optical microscope to produce images of larger sand-sized particles, and an atomic-force microscope to produce 3D images of the surface of particles as small as 100 microns across. Since the end of the mission, the team has been cataloguing individual particle sizes to understand more about the history of the Martian soil.

They estimated that the soil had only been exposed to liquid water for a maximum of 5,000 years by comparing their data with the slowest rate that clays could form on Earth.

The team found further evidence to support the idea that Martian soil has been largely dry throughout its history by comparing soil data from Mars, Earth and the Moon. The researchers deduced that the soil was being formed in a similar way on Mars and the Moon because they were able to match the distribution of soil particle sizes. On Mars, the team inferred that physical weathering by the wind as well as meteorites breaks down the soil into smaller particles. On the Moon, meteorite impacts break down rocks into soil, as there is no liquid water or atmosphere to wear down the particles.

…(Science Daily)

February 3, 2012 Posted by | Science, Space | , , , , | Leave a comment

Super-Earth Detected within Habitable Zone of Nearby Cold Star

An artistic conception of the two planets reported on in this paper: b and c. Planet c is the one that lies in the habitable zone of the star. Planet b is too hot to be habitable. (Credit: Images courtesy of Guillem Anglada-Escud)

An international team of scientists led by Carnegie’s Guillem Anglada-Escudé and Paul Butler has discovered a potentially habitable super-Earth orbiting a nearby star. The star is a member of a triple star system and has a different makeup than our Sun, being relatively lacking in metallic elements. This discovery demonstrates that habitable planets could form in a greater variety of environments than previously believed.

The team used public data from the European Southern Observatory and analyzed it with a novel data analysis method. They also incorporated new measurements from the Keck Observatory’s High Resolution Echelle Spectrograph and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope.

Their planet-finding technique involved measuring the small wobbles in a star’s orbit in response to a planet’s gravity. Anglada-Escudé and his team focused on an M-class dwarf star called GJ 667C, which is 22 light years away. It is a member of a triple-star system. The other two stars (GJ 667AB) are a pair of orange K dwarfs, with a concentration of heavy elements only 25% that of our Sun’s. Such elements are the building blocks of terrestrial planets so it was thought to be unusual for metal-depleted star systems to have an abundance of low mass planets.

GJ 667C had previously been observed to have a super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published. This orbit is too tight, and thus hot, to support life. The new study started with the aim of obtaining the orbital parameters of this super-Earth.

But in addition to this first candidate, the research team found the clear signal of a new planet (GJ 667Cc) with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth. The new planet receives 90% of the light that Earth receives. However, because most of its incoming light is in the infrared, a higher percentage of this incoming energy should be absorbed by the planet. When both these effects are taken into account, the planet is expected to absorb about the same amount of energy from its star that Earth absorbs from the Sun. This would allow surface temperatures similar to Earth and perhaps liquid water, but this extreme cannot be confirmed without further information on the planet’s atmosphere.

“This planet is the new best candidate to support liquid water and, perhaps, life as we know it,” Anglada-Escudé said.

The team notes that the system might also contain a gas-giant planet and an additional super-Earth with an orbital period of 75 days. However, further observations are needed to confirm these two possibilities. “With the advent of a new generation of instruments, researchers will be able to survey many M dwarf stars for similar planets and eventually look for spectroscopic signatures of life in one of these worlds.”

…(Science Daily)

February 3, 2012 Posted by | Science, Space | , , , , | Leave a comment

A New Way to Study Ground Fractures

Boise State University geophysics researchers have created a new way to study fractures by producing elastic waves, or vibrations, through using high-intensity light focused directly on the fracture itself. The new technique developed in the Physical Acoustics Lab at Boise State may help determine if there is a fluid, such as magma or water, or natural gas inside fractures in the Earth.

Typically, scientists create sound waves at the surface to listen for echoes from fractures in the ground, but this new technique could provide more accurate information about the cracks because sound does not have to travel to the fracture and back again. The new technique aims to enhance scientists’ abilities to image faults in the Earth, including those human-made through the process of hydraulic fracturing, or fracking.

The new method is explained in a paper that appears online in the journal Physical Review Letters.

“These concepts are of great importance in earthquake dynamics, but also in exploration of hydrocarbons,” said study coauthor Thomas Blum, a Boise State doctoral student. “If we can understand, for example, the microscopic structure of fracture points using this technique, we might be able to learn how, exactly, earthquakes happen. Scientists do not yet fully understand the structure of the faults, so if we could remotely sense the structure of faults, we might be able to learn more.”

Blum and Kasper van Wijk, associate professor of geosciences at Boise State, came up with the new technique by focusing laser light directly onto a fracture inside a transparent sample to create elastic waves. The researchers proved that laser-based ultrasonic techniques can “excite,” or cause vibrations, in the fracture. The result — jointly obtained with scientists at Colorado School of Mines and ConocoPhillips — opens up the possibility of measuring variations in the fracture and diagnosing the mechanical properties of fractures by directly exciting them.

…(Science Daily)

February 3, 2012 Posted by | Science, Seismic | , , , | Leave a comment

Rare ‘Ring of Fire’ Eclipse to be Visible from North America

Get out your calendar and make a big exclamation point on May 20.

That’s when an annular solar eclipse will turn the sun into a ring of fire.

This is the first solar eclipse visible from the United States in about 18 years, according to NASA. We’ve had our share of lunar eclipses in recent years, but solar eclipses happen when the moon passes in front of the sun, obscuring it from view.

The “ring of fire” effect will be visible as far north as Medford, Oregon and as far south as Lubbock, Texas. Throughout the zone –called the “path of annularity” – sky watchers will see the sun transformed into a a bright doughnut-like object.

The rest of the country west of the Mississippi (including Seattle) will witness a partial eclipse. That’s when the sun appears to be crescent-shaped as the moon passes by off-center.

NASA wants to remind you that this is not a total eclipse — when the moon entirely obscures the sun from view. The next total eclipse visible from the US happens in 2017. (Again, mark your calendar.)

…(Seattlepi)

February 2, 2012 Posted by | Science, Solar, Space | , , , , | Leave a comment

First Plants Caused Ice Ages, New Research Shows

New research reveals how the arrival of the first plants 470 million years ago triggered a series of ice ages. Led by the Universities of Exeter and Oxford, the study is published in Nature Geoscience.

The team set out to identify the effects that the first land plants had on the climate during the Ordovician Period, which ended 444 million years ago. During this period the climate gradually cooled, leading to a series of ‘ice ages’. This global cooling was caused by a dramatic reduction in atmospheric carbon, which this research now suggests was triggered by the arrival of plants.

Among the first plants to grow on land were the ancestors of mosses that grow today. This study shows that they extracted minerals such as calcium, magnesium, phosphorus and iron from rocks in order to grow. In so doing, they caused chemical weathering of Earth’s surface. This had a dramatic impact on the global carbon cycle and subsequently on the climate. It could also have led to a mass extinction of marine life.

The research suggests that the first plants caused the weathering of calcium and magnesium ions from silicate rocks, such as granite, in a process that removed carbon dioxide from the atmosphere, forming new carbonate rocks in the ocean. This cooled global temperatures by around five degrees Celsius.

In addition, by weathering the nutrients phosphorus and iron from rocks, the first plants increased the quantities of both these nutrients going into the oceans, fuelling productivity there and causing organic carbon burial. This removed yet more carbon from the atmosphere, further cooling the climate by another two to three degrees Celsius.

It could also have had a devastating impact on marine life, leading to a mass extinction that has puzzled scientists.

…(Science Daily)

February 1, 2012 Posted by | Climate, Science | , , , , | Leave a comment

   

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