Typhoons Trigger Slow Earthquakes

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ScienceDaily (June 12, 2009) — Scientists have made the surprising finding that typhoons trigger slow earthquakes, at least in eastern Taiwan. Slow earthquakes are non-violent fault slippage events that take hours or days instead of a few brutal seconds to minutes to release their potent energy. The researchers discuss their data in a study published the June 11, issue of Nature.

"From 2002 to 2007 we monitored deformation in eastern Taiwan using three highly sensitive borehole strainmeters installed 650 to 870 feet (200-270 meters) deep. These devices detect otherwise imperceptible movements and distortions of rock," explained coauthor Selwyn Sacks of Carnegie's Department of Terrestrial Magnetism. "We also measured atmospheric pressure changes, because they usually produce proportional changes in strain, which we can then remove."
Taiwan has frequent typhoons in the second half of each year but is typhoon free during the first 4 months. During the five-year study period, the researchers, including lead author Chiching Liu (Academia Sinica, Taiwan), identified 20 slow earthquakes that each lasted from hours to more than a day. The scientists did not detect any slow events during the typhoon-free season. Eleven of the 20 slow earthquakes coincided with typhoons. Those 11 were also stronger and characterized by more complex waveforms than the other slow events.
"These data are unequivocal in identifying typhoons as triggers of these slow quakes. The probability that they coincide by chance is vanishingly small," remarked coauthor Alan Linde, also of Carnegie.
How does the low pressure trigger the slow quakes? The typhoon reduces atmospheric pressure on land in this region, but does not affect conditions at the ocean bottom, because water moves into the area and equalizes pressure. The reduction in pressure above one side of an obliquely dipping fault tends to unclamp it. "This fault experiences more or less constant strain and stress buildup," said Linde. "If it's close to failure, the small perturbation due to the low pressure of the typhoon can push it over the failure limit; if there is no typhoon, stress will continue to accumulate until it fails without the need for a trigger."
"It's surprising that this area of the globe has had no great earthquakes and relatively few large earthquakes," Linde remarked. "By comparison, the Nankai Trough in southwestern Japan, has a plate convergence rate about 4 centimeters per year, and this causes a magnitude 8 earthquake every 100 to 150 years. But the activity in southern Taiwan comes from the convergence of same two plates, and there the Philippine Sea Plate pushes against the Eurasian Plate at a rate twice that for Nankai."
The researchers speculate that the reason devastating earthquakes are rare in eastern Taiwan is because the slow quakes act as valves, releasing the stress frequently along a small section of the fault, eliminating the situation where a long segment sustains continuous high stresses until it ruptures in a single great earthquake. The group is now expanding their instrumentation and monitoring for this research.
Adapted from materials provided by Carnegie Institution, via EurekAlert!, a service of AAAS.

Ancient Volcanic Eruptions Caused Global Mass Extinction

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ScienceDaily (May 30, 2009) — A previously unknown giant volcanic eruption that led to global mass extinction 260 million years ago has been uncovered by scientists at the University of Leeds.

The eruption in the Emeishan province of south-west China unleashed around half a million cubic kilometres of lava, covering an area 5 times the size of Wales, and wiping out marine life around the world.
Unusually, scientists were able to pinpoint the exact timing of the eruption and directly link it to a mass extinction event in the study published in Science. This is because the eruptions occurred in a shallow sea – meaning that the lava appears today as a distinctive layer of igneous rock sandwiched between layers of sedimentary rock containing easily datable fossilised marine life.
The layer of fossilised rock directly after the eruption shows mass extinction of different life forms, clearly linking the onset of the eruptions with a major environmental catastrophe.
The global effect of the eruption is also due to the proximity of the volcano to a shallow sea. The collision of fast flowing lava with shallow sea water caused a violent explosion at the start of the eruptions – throwing huge quantities of sulphur dioxide into the stratosphere.
"When fast flowing, low viscosity magma meets shallow sea it's like throwing water into a chip pan – there's spectacular explosion producing gigantic clouds of steam," explains Professor Paul Wignall, a palaeontologist at the University of Leeds, and the lead author of the paper.
The injection of sulphur dioxide into the atmosphere would have lead to massive cloud formation spreading around the world - cooling the planet and ultimately resulting in a torrent of acid rain. Scientists estimate from the fossil record that the environmental disaster happened at the start of the eruption.
"The abrupt extinction of marine life we can clearly see in the fossil record firmly links giant volcanic eruptions with global environmental catastrophe, a correlation that has often been controversial," adds Professor Wignall.
Previous studies have linked increased carbon dioxide produced by volcanic eruptions with mass extinctions. However, because of the very long term warming effect that occurs with increased atmospheric carbon dioxide (as we see with current climate change) the causal link between global environmental changes and volcanic eruptions has been hard to confirm.
This work was done in collaboration with the Chinese University of Geosciences in Wuhan and funded by a grant from the Natural Environment Research Council, UK.
Journal reference:
Paul B. Wignall, Yadong Sun, David P. G. Bond, Gareth Izon, Robert J. Newton, Stéphanie Védrine, Mike Widdowson, Jason R. Ali, Xulong Lai, Haishui Jiang, Helen Cope, and Simon H. Bottrell. Precise coincidence of explosive volcanism, mass extinction and carbon isotope fluctuations in the Middle Permian of China. Science, 2009; DOI: 10.1126/science.1171956
Adapted from materials provided by University of Leeds.

Huge undersea mountain found off Indonesia: scientists

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This aerial view shows new homes being constructed to the north of Banda Aceh on the island of Sumatra in 2006. A massive underwater mountain discovered off the Indonesian island of Sumatra could be a volcano with potentially catastrophic power, a scientist said Friday.
A massive underwater mountain discovered off the Indonesian island of Sumatra could be a volcano with potentially catastrophic power, a scientist said Friday.

Indonesian government marine geologist Yusuf Surachman said the mountain was discovered earlier this month about 330 kilometres (205 miles) west of Bengkulu city during research to map the seabed's seismic faultlines.
The cone-shaped mountain is 4,600 metres (15,100 feet) high, 50 kilometres in diameter at its base and its summit is 1,300 metres below the surface, he said.
"It looks like a volcano because of its conical shape but it might not be. We have to conduct further investigations," he told AFP.
He denied reports that researchers had confirmed the discovery of a new volcano, insisting that at this stage it could only be described as a "seamount" of the sort commonly found around the world.
"Whether it's active or dangerous, who knows?" he added.
The ultra-deep geological survey was conducted with the help of French scientists and international geophysical company CGGVeritas.
The scientists hope to gain a clearer picture of the undersea lithospheric plate boundaries and seafloor displacement in the area, the epicentre of the catastrophic Asian quake and tsunami of 2004.
The tsunami killed more than 220,000 people across Asia, including 168,000 people in Aceh province on the northern tip of Sumatra.
Indonesia is on the so-called Pacific "Ring of Fire," where the meeting of continental plates causes high volcanic and seismic activity.
(c) 2009 AFP

Changes In The Sun Are Not Causing Global Warming, New Study Shows

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ScienceDaily (May 12, 2009) — With the U.S. Congress beginning to consider regulations on greenhouse gases, a troubling hypothesis about how the sun may impact global warming is finally laid to rest.

Carnegie Mellon University's Peter Adams along with Jeff Pierce from Dalhousie University in Halifax, Canada, have developed a model to test a controversial hypothesis that says changes in the sun are causing global warming.
The hypothesis they tested was that increased solar activity reduces cloudiness by changing cosmic rays. So, when clouds decrease, more sunlight is let in, causing the earth to warm. Some climate change skeptics have tried to use this hypothesis to suggest that greenhouse gases may not be the global warming culprits that most scientists agree they are.
In research published in Geophysical Research Letters, and highlighted in the May 1 edition of Science, Adams and Pierce report the first atmospheric simulations of changes in atmospheric ions and particle formation resulting from variations in the sun and cosmic rays. They find that changes in the concentration of particles that affect clouds are 100 times too small to affect the climate.
"Until now, proponents of this hypothesis could assert that the sun may be causing global warming because no one had a computer model to really test the claims," said Adams, a professor of civil and environmental engineering at Carnegie Mellon.
"The basic problem with the hypothesis is that solar variations probably change new particle formation rates by less than 30 percent in the atmosphere. Also, these particles are extremely small and need to grow before they can affect clouds. Most do not survive to do so," Adams said.
Despite remaining questions, Adams and Pierce feel confident that this hypothesis should be laid to rest. "No computer simulation of something as complex as the atmosphere will ever be perfect," Adams said. "Proponents of the cosmic ray hypothesis will probably try to question these results, but the effect is so weak in our model that it is hard for us to see this basic result changing."
Journal references:
J. R. Pierce and P. J. Adams. Can cosmic rays affect cloud condensation nuclei by altering new particle formation rates? Geophys. Res. Lett., 2009; (in press) DOI: 10.1029/2009GL037946
Richard A. Kerr. Study Challenges Cosmic Ray-Climate Link. Science, 2009; 324 (5927): 576 DOI: 10.1126/science.324_576b
Adapted from materials provided by Carnegie Mellon University.

Origin Of 'Breathable' Atmosphere Half A Billion Years Ago Discovered

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http://www.sciencedaily.com/releases/2007/10/071029094320.htm

ScienceDaily (Oct. 30, 2007) — Ohio State University geologists and their colleagues have uncovered evidence of when Earth may have first supported an oxygen-rich atmosphere similar to the one we breathe today.

The study suggests that upheavals in the earth's crust initiated a kind of reverse-greenhouse effect 500 million years ago that cooled the world's oceans, spawned giant plankton blooms, and sent a burst of oxygen into the atmosphere.
That oxygen may have helped trigger one of the largest growths of biodiversity in Earth's history.
Matthew Saltzman, associate professor of earth sciences at Ohio State, reported the findings October 28 at the meeting of the Geological Society of America in Denver.
For a decade, he and his team have been assembling evidence of climate change that occurred 500 million years ago, during the late Cambrian period. They measured the amounts of different chemicals in rock cores taken from around the world, to piece together a complex chain of events from the period.
Their latest measurements, taken in cores from the central United States and the Australian outback, revealed new evidence of a geologic event called the Steptoean Positive Carbon Isotope Excursion (SPICE).
Amounts of carbon and sulfur in the rocks suggest that the event dramatically cooled Earth's climate over two million years -- a very short time by geologic standards. Before the event, the Earth was a hothouse, with up to 20 times more carbon dioxide in the atmosphere compared to the present day. Afterward, the planet had cooled and the carbon dioxide had been replaced with oxygen. The climate and atmospheric composition would have been similar to today.
“If we could go back in time and walk around in the late Cambrian, this seems to be the first time we would have felt at home,” Saltzman said. “Of course, there was no life on land at the time, so it wouldn't have been all that comfortable.”
The land was devoid of plants and animals, but there was life in the ocean, mainly in the form of plankton, sea sponges, and trilobites. Most of the early ancestors of the plants and animals we know today existed during the Cambrian, but life wasn't very diverse.
Then, during the Ordovician period, which began around 490 million years ago, many new species sprang into being. The first coral reefs formed during that time, and the first true fish swam among them. New plants evolved and began colonizing land.
“If you picture the evolutionary ‘tree of life,' most of the main branches existed during the Cambrian, but most of the smaller branches didn't get filled in until the Ordovician,” Saltzman said. “That's when animal life really began to develop at the family and genus level.” Researchers call this diversification the “Ordovician radiation.”
The composition of the atmosphere has changed many times since, but the pace of change during the Cambrian is remarkable. That's why Saltzman and his colleagues refer to this sudden influx of oxygen during the SPICE event as a “pulse” or “burst.”
“After this pulse of oxygen, the world remained in an essentially stable, warm climate, until late in the Ordovician,” Saltzman said.
He stopped short of saying that the oxygen-rich atmosphere caused the Ordovician radiation.
“We know that oxygen was released during the SPICE event, and we know that it persisted in the atmosphere for millions of years -- during the time of the Ordovician radiation -- so the timelines appear to match up. But to say that the SPICE event triggered the diversification is tricky, because it's hard to tell exactly when the diversification started,” he said.
“We would need to work with paleobiologists who understand how increased oxygen levels could have led to a diversification. Linking the two events precisely in time is always going to be difficult, but if we could link them conceptually, then it would become a more convincing story.”
Researchers have been trying to understand the sudden climate change during the Cambrian period ever since Saltzman found the first evidence of the SPICE event in rock in the American west in 1998. Later, rock from a site in Europe bolstered his hypothesis, but these latest finds in central Iowa and Queensland, Australia, prove that the SPICE event occurred worldwide.
During the Cambrian period, most of the continents as we know them today were either underwater or part of the Gondwana supercontinent, Saltzman explained. Tectonic activity was pushing new rock to the surface, where it was immediately eaten away by acid rain. Such chemical weathering pulls carbon dioxide from the air, traps the carbon in sediments, and releases oxygen -- a kind of greenhouse effect in reverse.
“From our previous work, we knew that carbon was captured and oxygen was released during the SPICE event, but we didn't know for sure that the oxygen stayed in the atmosphere,” Saltzman said.
They compared measurements of inorganic carbon -- captured during weathering -- with organic carbon -- produced by plankton during photosynthesis. And because plankton contain different ratios of the isotopes of carbon depending on the amount of oxygen in the air, the geologists were able to double-check their estimates of how much oxygen was released during the period, and how long it stayed in the atmosphere.
They also studied isotopes of sulfur, to determine whether much of the oxygen being produced was re-captured by sediments.
It wasn't.
Saltzman explained the chain of events this way: Tectonic activity led to increased weathering, which pulled carbon dioxide from the air and cooled the climate. Then, as the oceans cooled to more hospitable temperatures, the plankton prospered -- and in turn created more oxygen through photosynthesis.
“It was a double whammy,” he said. “There's really no way around it when we combine the carbon and sulfur isotope data -- oxygen levels dramatically rose during that time.”
What can this event tell us about climate change today? “Oxygen levels have been stable for the last 50 million years, but they have fluctuated over the last 500 million,” Saltzman said. “We showed that the oxygen burst in the late Cambrian happened over only two million years, so that is an indication of the sensitivity of the carbon cycle and how fast things can change.”
Global cooling may have boosted life early in the Ordovician period, but around 450 million years ago, more tectonic activity -- most likely, the rise of the Appalachian Mountains -- brought on a deadly ice age. So while most of the world's plant and animal species were born during the Ordovician period, by the end of it, more than half of them had gone extinct.
Coauthors on this study included Seth Young, a graduate student in earth sciences at Ohio State; Ben Gill, a graduate student, and Tim Lyons, professor of earth sciences, both at the University of California, Riverside; Lee Kump, professor of geosciences at Penn State University; and Bruce Runnegar, professor of paleontology at the University of California, Los Angeles.
Adapted from materials provided by Ohio State University.

Fausto Intilla

www.oloscience.com

Geologists Recover Rocks Yielding Unprecedented Insights Into San Andreas Fault

Source:

http://www.sciencedaily.com/releases/2007/10/071004143120.htm

Science Daily — For the first time, geologists have extracted intact rock samples from 2 miles beneath the surface of the San Andreas Fault, the infamous rupture that runs 800 miles along the length of California.

Never before have scientists had available for study rock samples from deep inside one of the actively moving tectonic plate-bounding faults responsible for the world's most damaging earthquakes. Now, with this newly recovered material, scientists hope to answer long-standing questions about the fault's composition and properties.
Altogether, the geologists retrieved 135 feet of 4-inch diameter rock cores weighing roughly 1 ton. They were brought to the surface through a research borehole drilled more than 2.5 miles into the Earth. The last of the cores was brought to the surface in the predawn hours of Sept. 7.
Scientists seeking to understand how the great faults bounding Earth's vast tectonic plates evolve and generate earthquakes have always had to infer the processes through indirect means. Up until now, they could only work with samples of ancient faults exposed at the Earth's surface after millions of years of erosion and uplift, together with computer simulations and laboratory experiments approximating what they think might be happening at the depths at which earthquakes occur.
"Now we can hold the San Andreas Fault in our hands," said Mark Zoback, the Benjamin M. Page Professor in Earth Sciences at Stanford. "We know what it's made of. We can study how it works."
Zoback is one of three co-principal investigators of the San Andreas Fault Observatory at Depth (SAFOD) project, which is establishing the world's first underground earthquake observatory. William Ellsworth and Steve Hickman, geophysicists with the U.S. Geological Survey (USGS) in Menlo Park, Calif., are the other co-principal investigators.
SAFOD, which first broke ground in 2004, is a major research component of EarthScope, a National Science Foundation-funded program being carried out in collaboration with the USGS and NASA to investigate the forces that shape the North American continent and the physical processes controlling earthquakes and volcanic eruptions.
"This is tremendously exciting. Obtaining cores from the actively slipping San Andreas Fault is truly unprecedented and will allow truly transformative research and discoveries," said Kaye Shedlock, EarthScope program director at the National Science Foundation.
In the next phase of the experiment, the science team will install an array of seismic instruments in the 2.5-mile-long borehole that runs from the Pacific plate on the west side of the fault into the North American plate on the east. By placing sensors next to a zone that has been the source of many small temblors, scientists will be able to observe the earthquake generation process with unprecedented acuity. They hope to keep the observatory operating for the next 10 to 20 years.
Studying the San Andreas Fault is important because, as Zoback noted, "The really big earthquakes occur on plate boundaries like the San Andreas Fault." The SAFOD site, located about 23 miles northeast of Paso Robles near the tiny town of Parkfield, sits on a particularly active section of the fault that moves regularly. But it does not produce large earthquakes. Instead, it moves in modest increments by a process called creep, in which the two sides of the fault slide slowly past one another, accompanied by occasional small quakes, most of which are not even felt at the surface.
One of the big questions the researchers seek to answer is how, when most of the fault moves in violent, episodic upheavals, can there be a section where the same massive tectonic plates seem, by comparison, to gently tiptoe past each other with the delicate tread of little cat feet"
"There have been many theories about why the San Andreas Fault slides along so easily, none of which could be tested directly until now," Hickman said. Some posit the presence of especially slippery clays, called smectites. Others suggest there may be high water pressure along the fault plane lubricating the surface. Still others note the presence of a mineral called serpentine exposed in several places along the surface trace of the fault, which-if it existed at depth-could both weaken the fault and cause it to creep.
Zoback said the correlation between the occurrence of serpentine, a metamorphosed remnant of old oceanic crust, and the slippery nature of the fault motion in the area has been the subject of speculation for more than 40 years. However, it has never been demonstrated that serpentine actually occurs along the active San Andreas at depth, and the mechanism by which serpentine might limber up the fault was unknown.
Then, in 2005, when the SAFOD drill pierced the zone of active faulting using rotary drilling (which grinds up the rock into tiny fragments), mineralogist Diane Moore of the USGS detected talc in the rock cuttings brought up to the surface. This finding was published in the Aug. 16, 2007, issue of Nature.
"Talc is one of the slipperiest, weakest minerals ever studied," Hickman said.
Might the same mineral that helps keep a baby's bottom smooth also be smoothing the way for the huge tectonic plates" Chemically, it's possible, for when serpentine is subjected to high temperatures in the presence of water containing silica, it forms talc.
Serpentine might also control how faults behave in other ways. "Serpentine can dissolve in ground water as fault particles grind past each other and then crystallize in nearby open pore spaces, allowing the fault to creep even under very little pressure," Hickman said.
The SAFOD borehole cored into two active traces of the fault this summer, both contained within a broad fault "zone" about 700 feet wide. The deeper of the two active fault zones, designated 10830 for its distance in feet from the surface as measured along the curving borehole, yielded an 8-foot-long section of very fine-grained powder called fault gouge. Such gouge is common in fault zones and is produced by the grinding of rock against rock. "What is remarkable about this gouge is that it contains abundant fragments of serpentine that appear to have been swept up into the gouge from the adjacent solid rock," Hickman said. "The serpentine is floating around in the fault gouge like raisins in raisin pudding."
The only way to know what role serpentine, talc or other exotic minerals play in controlling the behavior of the San Andreas Fault is to study the SAFOD core samples in the laboratory.
"To an earthquake scientist, these cores are like the Apollo moon rocks," Hickman said. "Scientists from around the world are anxious to get their hands on them in the hope that they can help solve the mystery of how this major, active plate boundary works."
Will these new samples allow scientists to predict earthquakes" The short answer is no. But research on these samples could provide clues to answer the question of whether earthquakes are predictable. The observatory will allow scientists to begin to address whether there are precursory phenomena occurring within the fault zone.
The other fault zone, called 10480, contains 3 feet of fault gouge. It also produces small earthquakes at a location about 300 feet below the borehole. "Remarkably, we observe the same earthquake rupturing at the same spot on the fault year after year," Ellsworth said. This repeating earthquake, always about a magnitude 2, will be the focus of the observatory to be installed inside the fault in 2008.
Sensitive seismometers and tiltmeters to be installed in the SAFOD borehole directly above the spot that ruptures will observe for the first time the birthing process of an earthquake from the zone where the earthquake energy accumulates. Preliminary observations made in 2006 already have revealed the tiniest earthquakes ever observed-so small they have negative magnitudes.
In early December, a "sample party" will be held at the USGS office in Menlo Park, where the cores will be on display and scientists will offer their proposals to do research projects in a bid to be allowed to analyze part of the core.
Zoback said most of the initial testing will be nondestructive in order to preserve the samples for as long as possible. "But then, some of the material will be made available for testing that simulates earthquakes and fault slip in the lab," he said.
When not being examined, the core samples will be refrigerated and kept moist to prevent the cores and the fluid in them from being disturbed.
Some of the cores will be on display at the press conference to be held Oct. 4 at Stanford University in Tresidder Union's Oak Room.
In addition to funding from the National Science Foundation, USGS and Stanford University, the SAFOD project also has been supported financially by the International Continental Scientific Drilling Program.
Note: This story has been adapted from material provided by Stanford University.

Fausto Intilla

www.oloscience.com

Devastating Earthquake May Threaten Middle East's Near Future, Geologist Predicts

Source:

http://www.sciencedaily.com/releases/2007/10/071003142432.htm

Science Daily — The best seismologists in the world don’t know when the next big earthquake will hit. But a Tel Aviv University geologist suggests that earthquake patterns recorded in historical documents of Middle Eastern countries indicate that the region’s next significant quake is long overdue.

A major quake of magnitude seven on the Richter scale in the politically-fragile region of the Middle East could have dire consequences for precious holy sites and even world peace, says Tel Aviv University geologist Dr. Shmulik Marco. In light of this imminent danger, Marco, from the school’s Department of Geophysics and Planetary Sciences, has taken an historical approach to earthquake forecasting by using ancient records from the Vatican and other religious sources in his assessment. The past holds the key to the future, he says.
“All of us in the region should be worried,” explains Marco, who dedicates his career to piecing together ancient clues.
Based on the translations of hundreds of documents -- some of the originals of which he assumes reside in Vatican vaults -- Marco has helped determine that a series of devastating earthquakes have hit the Holy Land over the last two thousand years. The major ones were recorded along the Jordan Valley in the years 31 B.C.E., 363 C.E., 749 C.E., and 1033 C.E. “So roughly,” warns Marco, “we are talking about an interval of every 400 years. If we follow the patterns of nature, a major quake should be expected any time because almost a whole millennium has passed since the last strong earthquake of 1033.”
Written by monks and clergy, the documents, which span about two millenia, can help determine the location and impact of future quakes on several fault planes cutting through Israel and its neighboring countries, Marco believes. “We use the records, written in churches and monasteries or by hermits in the desert, to find patterns,” he says. Marco credits the help of an international team of historians, who have deciphered the Latin, Greek, and Arabic of the original correspondence.
He continues, “Even if these papers were not ‘officially’ recording history, they hold a lot of information. ... Some are letters to Europe asking for funding of church repairs. And while many of these accounts are told in an archaic religious manner, they help us confirm the dates and location of major calamities. Following these patterns in the past can be a good predictor of the future.”
One of the most cited Christian chroniclers in history upon whom Marco bases some of his conclusions is a ninth-century Byzantine aristocratic monk named Theophanes, venerated today by Catholics. In one manuscript, Theophanes wrote, “A great earthquake in Palestine, by the Jordan and in all of Syria on 18 January in the 4th hour. Numberless multitudes perished, churches and monasteries collapsed especially in the desert of the Holy City.”
While Christian sources helped Marco confirm ancient catastrophes and cast light on future ones, Jewish sources from the Bible also gave him small pieces of the puzzle. A verse in Zachariah (Ch. 14) describes two instances of earthquakes, one of which split apart the Mount of Olives, he says. Muslim clergy have also collected ancient correspondence, which further broadens the picture.
”Earthquakes are a manifestation of deeper processes inside the earth,” Marco says. “My questions and analysis examine how often they occur and whether there is pattern to them, temporally or spatially. I am looking for patterns and I can say that based on ancient records, the pattern in Israel around the Dead Sea region is the most disturbing to us.
“When it strikes and it will this quake will affect Amman, Jordan as well as Ramallah, Bethlehem, and Jerusalem. Earthquakes don’t care about religion or political boundaries,” Marco concludes.
Note: This story has been adapted from material provided by Tel Aviv University.

Fausto Intilla

www.oloscience.com

Deep Earth Model Challenged By New Experiment

Source:

http://www.sciencedaily.com/releases/2007/09/070920145537.htm

Science Daily — In the first experiments able to mimic the crushing, searing conditions found in Earth's lower mantle, and simultaneously probe tell-tale properties of iron, scientists* have discovered that material there behaves very differently than predicted by models. The research also points to the likelihood of a new zone deep in the Earth.

Surface phenomena such as volcanoes and earthquakes are generated by what goes on in Earth's interior. To understand some of these surface dynamics, scientists have to probe deep into the planet. The lower mantle is between 400 and 1,740 miles deep (650 km- 2,800 km) and sits atop the outer core.
Coauthor of the paper, Viktor Struzhkin of the Carnegie Institution's Geophysical Laboratory explains: "The deeper you go, the higher the pressures and temperatures become. Under these extreme conditions, the atoms and electrons of the rocks become squeezed so close together that they interact very peculiarly. In fact, spinning electrons in iron, which is prevalent throughout the inner Earth, are forced to pair up. When this spin state changes from unpaired electrons--called a high-spin state--to paired electrons--a low-spin state--the density, sound velocities, conductivity, and other properties of the materials can change. Understanding these conditions helps scientists piece together the complex puzzle of the interior/surface interactions."
The pressures in the lower mantle are brutal, ranging from about 230,000 times the atmospheric pressure at sea level (23 GPa), to almost 1.35 million times sea-level pressure (135 GPa). The heat is equally extreme--from about 2,800 to 6,700 degrees Fahrenheit (1800 K--4000 K).
Using a laser-heated diamond anvil cell to heat and compress the samples, the scientists subjected ferropericlase to almost 940,000 atmospheres and 3,140 °F. They analyzed it using so-called X-ray emission spectroscopy. As its name suggests, ferropericlase is iron-laden.
It is also the second most prevalent material found in the lower mantle. Previous to this study, ferropericlase has been subjected to high pressures, but only to room temperatures. The new experiments are the highest pressures and temperatures attained to probe the spin state of iron in the mineral at lower-mantle conditions.
Under the less-intense conditions of the former experiments, the high-spin to low-spin transition occurs in a narrow pressure range. In the new study, however, both spin states coexisted in the same crystal structure and the spin transition was also continuous over a large pressure range, indicating that the mineral is in a complex state over a large range in depth in the planet.
"We were expecting to find a transition zone, but did not know how extended it may be in the Earth's mantle," commented Struzhkin. "Our findings suggest that there is a region or 'spin-transition zone' from about 620 miles to 1,365 miles deep, where high spin, unpaired electrons, transition to low spin, paired electrons. The transitioning appears to be continuous over these depths. At pressures representing a lower depth of about 1,365 miles the transition stops and ferropericlase is dominated by low-spin electrons."
Since measurements that scientists use to determine the composition and density of the inner Earth, such as sound velocities, are influenced by the ratio of high-spin/low- spin states, the new finding calls into question the traditional techniques for modeling this region of the planet.
In addition, a continuous spin transition zone may explain some interesting experimental findings including why there has been no significant iron partitioning, or separating, into ferropericlase or perovskite, the most prevalent mineral in the region. The research also suggests that the depth of the transition zone is less than scientists had speculated.
The existence of this transition zone may also account for seismic-wave behavior at those depths. The fact that the lowermost area is dominated by denser low-spin material could also affect the temperature stability of mantle upwellings--the generators of volcanic hotspots, such as those in Hawaii.
"This paper solves only part of the puzzle," cautioned Struzhkin. "Since the major lower mantle mineral perovskite has not been measured yet with this technique, we know there are more surprises to come."
"The spin transition zone of iron needs to be considered in future models of the lower mantle," said Choong-Shik Yoo, a former staff member at LLNL and now a professor at Washington State University. "In the past, geophysicists had neglected the effects of the spin transition when studying the Earth's interior.
Since we identified this zone, the next step is to study the properties of lower mantle oxides and silicates across the zone. This research also calls for future seismic and geodynamic tests in order to understand the properties of the spin transition zone."
"The benchmark techniques developed here have profound implications for understanding the electronic transitions in lanthanoid and actinoid compounds under extreme conditions because their properties would be affected by the electronic transitions," said Valentin Iota, a staff member in LLNL's Physics and Advanced Technologies Directorate.
The work is published in the September 21, 2007, issue of Science.
*Authors on this paper are Jung-Fu Lin, Lawrence Livermore National Laboratory (LLNL); György Vankó, KFKI Research Institute for Particle and Nuclear Physics and the European Synchrotron Radiation Facility; Steven Jacobsen, Northwestern University; Viktor Struzhkin, Carnegie Institution's Geophysical Laboratory; Vitali Prakapenka, University of Chicago; Alexie Kuznetsov, University of Chicago; and Choong-Shik Yoo LLNL.
Note: This story has been adapted from a news release issued by Carnegie Institution.

Fausto Intilla

www.oloscience.com

Does Underground Water Regulate Earthquakes?

Source:

http://www.sciencedaily.com/releases/2007/09/070915105639.htm

Science Daily — Earthquakes happen to be surface (shallow-focus), intermediate and deep ones. Seismologists mark out the boundary between the first two types at the depth of about 70 kilometers, its nature being still unclear.
Russian researchers, specialists of the Institute of Maritime Geology and Geophysics (Far-Eastern Branch, Russian Academy of Sciences), Geophysical Center of the Russian Academy of Sciences and the P.P. Shirshov Institute of Oceanology (Russian Academy of Sciences) have put forward a hypothesis that the seismic boundary is simultaneously the lower boundary of hydrosphere. The earthquakes character depends on underground water.
Earthquakes taking place “at different sides of the boundary” differ from each other not only by the depth. Shallow-focus earthquakes – they account for about 85% of all recorded events - often take place under the influence of periodic external effects, for example, rising tides, which disturb the entire lithosphere of the Earth. Periodicity is not inherent to deeper earthquakes, they always occur by chance. The conclusion was made by the researchers who had analyzed the world ISC/NEIC catalogues data that covers the 1964-2005 period and takes into account about 80,000 events.
Seismologists connect existence of the 70-kilometer boundary with water state changes in the interior of the Earth. The deeper the water molecules are located, the more compressed they are. At the depth of about 70 kilometers, the water compression strain index increases up to 1.3. This is the way water molecules are squeezed in the crystal lattice. Above this boundary, water exists mainly in free phase, below the boundary – water embeds into the rock crystallite composition.
The rock containing free water (above the boundary) promptly reacts to periodic tidal effects, even the faintest ones. Pressure changes and respective environment density changes cause formation of a crack system, where free water rushes to. The cracks widen, increase, and rock decay gives birth to a seismic focus. In the rock, where free water is absent (below the boundary), weak tidal effects are not accumulated and deformation does not grow.
So, the seismic boundary at the depth of about 70 kilometers (where, according to the researchers’ assumption, the lower hydrosphere boundary runs) separates the events that are able to react to external action and the ones incapable of such reaction. Therefore, this boundary separates different types of earthquakes. However, it is still a hypothesis that requires experimental validation.
Note: This story has been adapted from a news release issued by Russian Academy Of Sciences.

Fausto Intilla
www.oloscience.com