7.5 mag quake in northern Peru

The USGS (United States Geological Survey) this morning reported a 7.5 mag quake in northern Peru

Magnitude 7.5 
Date-Time Monday, September 26, 2005 at 01:55:34 (UTC)
= Coordinated Universal Time 
Sunday, September 25, 2005 at 8:55:34 PM 
= local time at epicenter 
Time of Earthquake in other Time Zones  
Location 5.657°S, 76.366°W 
Depth 85.4 km (53.1 miles) 
Region NORTHERN PERU 
Distances 
75 km (50 miles) NE of Moyobamba, Peru
175 km (110 miles) ENE of Chachapoyas, Peru
645 km (400 miles) SSE of QUITO, Ecuador
715 km (445 miles) N of LIMA, Peru
 
Location Uncertainty horizontal +/- 7.4 km (4.6 miles); depth +/- 14.2 km (8.8 miles) 
Parameters Nst=186, Nph=186, Dmin=701.4 km, Rmss=0.97 sec, Gp= 40°,
M-type=moment magnitude (Mw), Version=6  
Source USGS NEIC (WDCS-D)
 
Event ID usdlad

I also stumbled across this illustrated earthquake glossary at the USGS

May be useful to some
- posted by Affenhänger @ 9/25/2005 05:08:00 PM 0 comments links to this post

 
Word Up: Mittelmeer-Mjösen-Zone/European Cenozoic Rift System

Deutsch:

Der Mittelmeer-Mjösen-Zone ist benannt nach dem Mjösa-See in Norwegen bei Oslo. Es handelt sich um eine große europäische Bruchzone, die Mitteleuropa auf einer Länge von 2.000 km durchzieht. Sie erstreckt sich vom Mittelmeer über den Rhônegraben durch die Burgundische Pforte in den Oberrheingraben, von dort setzt sie sich über das Neuwieder Becken, die Niederrheinische Bucht und den Holländischen Zentralgraben bis in den Nordatlantik fort (BRUNOTTE et al. 1994).

Geändert nach Landesumweltamt Nordrhein-Westphalen, Merkblatt Nr. 41, Morphologisches Leitbild Niederrhein

English:

The European Cenozoic Rift System is a major rift zone that traverses central Europe for a distance of approx. 2000 km from the Mediterranean coast in the south of France, near the Rhône delta, to Lake Mjøsa, near Oslo, Norway's largest freshwater lake. The Upper Rhine Graben, as well as smaller German grabens such as the Leine Valley Graben, belong to this rift system.

- posted by Affenhänger @ 9/23/2005 08:49:00 PM 0 comments links to this post

 
MELT Data Sheds New and Surprising Light on Birth of Oceanic Plates

In the first joint interpretation of data from the landmark MELT study, a team of scientists including Donald Forsyth of Brown University has found unexpected changes in the patterns of seismic velocity and electrical conductivity near the East Pacific Rise, changes due to dehydration and cooling. Results are published in Nature.

PROVIDENCE, R.I. — The East Pacific Rise, a vast volcanic mountain range submerged in the eastern Pacific Ocean, is one of the fastest seafloor factories on the planet. Here, along a rocky spine that runs about 1,000 miles west of South America, oceanic crust is created from magma bubbling up from deep within Earth’s interior.

Forces that shape these young oceanic plates have come into clearer focus through research conducted by scientists at the Woods Hole Oceanographic Institution, Brown University and the Japan Agency for Marine-Earth Science and Technology.

The MELT Project
(Mantle Electromagnetic and Tomography)
Data from 81 instruments on the seafloor has yielded important new understandings of how the Earth’s crust is formed.

--------------------------------------------------------------------------------

The research represents the first time that seismic and electromagnetic data were analyzed in tandem from [the] 1995 Mantle Electromagnetic and Tomography, or MELT, Experiment. MELT employed 51 ocean-bottom seismometers and 30 magnetotelluric receivers two miles under the sea to measure sound waves and magnetic fields along the East Pacific Rise, making it one of the largest marine geophysical experiments ever conducted.

In a paper published in Nature, the team notes that in rock down to a depth of about 60 kilometers below the ocean floor, electrical currents conduct poorly and sound waves travel rapidly. Deeper down, beyond 60 kilometers, there is a dramatic increase in electrical conductivity, and sound waves travel at their slowest.

A switch in seismic and electrical properties with depth was expected. Researchers were surprised, however, at how close to the East Pacific Rise this structure develops and how little it changes with increasing distance from the rise.

Brown marine geophysicist Donald Forsyth said the team, led by Robert Evans from the Woods Hole Oceanographic Institution, has a theory about the cause of the sudden compositional changes at 60 kilometers: dehydration.

As magma migrates to the surface to form crust at the rise, it leaves behind a dry, residual layer about 60 kilometers thick. This change from "dry" surface rock to "damp" rock below it increases electrical conductivity and slows seismic velocity, the researchers write.

Here is what they did not expect: These changes occur, the team found, less than 100 kilometers away from the highest point on the ridge. And the seismic and electrical measurements remained nearly constant at least about 500 kilometers away from the crest.

Separating seafloor guides magma up to mid-ocean ridges such as the East Pacific Rise, where the molten rock erupts, fans out along the ocean floor and cools to form new crust. Cooling allows sound waves and electrical currents to travel faster. But scientists thought this cooling – and the resulting changes in the rock – would be gradual.

"About two-thirds of the Earth’s surface is oceanic crust – and it is all formed at ridges," Forsyth said. "So this work helps us better understand the basic processes of how this crust is formed."

The National Science Foundation funded MELT and the latest research.

######
Go here to read the original article, with hyperlinks and graphics.
- posted by Affenhänger @ 9/23/2005 07:32:00 PM 0 comments links to this post

 
The "sauropod" from the Albian of Mesnil-Saint-Père (Aube, France): a pliosaur, not a dinosaur

The peerless Carnets de Géologie has announced the publication of a new "memoir":

Buffetaut E., Colleté C., Dubus B., Petit J.-L. (2005).- The "sauropod" from the Albian of Mesnil-Saint-Père (Aube, France): a pliosaur, not a dinosaur.- Carnets de Géologie - Notebooks on Geology, Brest, Letter 2005/01 (CG2005_L01), 6 p., 2 fig.

Brief abstract
A vertebra from the Albian of Mesnil-Saint-Père (Aube, eastern Paris Basin), previously identified as the first caudal of a sauropod dinosaur, is shown to be a dorsal vertebra of a large pliosaur. The specimen resembles vertebrae from the Albian of England and eastern France that have been referred to the pliosaur Polyptychodon, a taxon in need of revision.

The complete memoir can be accessed here (html). It can also be downloaded in PDF format.
- posted by Affenhänger @ 9/21/2005 06:09:00 PM 0 comments links to this post

 
New study at GreenFacts.org

GreenFacts.org, previously noted by me in November 2004, has just released a new online study on Air Pollution, gathering scientific facts on three important air pollutants: nitrogen dioxide, ozone, and particulate matter. In October 2005 the World Health Organization (WHO) will reconsider current air quality guidelines. Does the latest research warrant new standards to better protect our health?
- posted by Affenhänger @ 9/18/2005 09:30:00 PM 0 comments links to this post

 
Calculations favor reducing atmosphere for early earth

Was Miller-Urey experiment correct?

By Tony Fitzpatrick

Sept. 7, 2005 — Using primitive meteorites called chondrites as their models, earth and planetary scientists at Washington University in St. Louis have performed outgassing calculations and shown that the early Earth's atmosphere was a reducing one, chock full of methane, ammonia, hydrogen and water vapor.

In making this discovery Bruce Fegley, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, and Laura Schaefer, laboratory assistant, reinvigorate one of the most famous and controversial theories on the origins of life, the 1953 Miller-Urey experiment, which yielded organic compounds necessary to evolve organisms.

Chondrites are relatively unaltered samples of material from the solar nebula, According to Fegley, who heads the University's Planetary Chemistry Laboratory, scientists have long believed them to be the building blocks of the planets. However, no one has ever determined what kind of atmosphere a primitive chondritic planet would generate.

"We assume that the planets formed out of chondritic material, and we sectioned up the planet into layers, and we used the composition of the mix of meteorites to calculate the gases that would have evolved from each of those layers," said Schaefer. "We found a very reducing atmosphere for most meteorite mixes, so there is a lot of methane and ammonia."

In a reducing atmosphere, hydrogen is present but oxygen is absent. For the Miller-Urey experiment to work, a reducing atmosphere is a must. An oxidizing atmosphere makes producing organic compounds impossible. Yet, a major contingent of geologists believe that a hydrogen-poor, carbon dioxide-rich atmosphere existed because they use modern volcanic gases as models for the early atmosphere. Volcanic gases are rich in water, carbon dioxide, and sulfur dioxide but contain no ammonia or methane.

"Geologists dispute the Miller-Urey scenario, but what they seem to be forgetting is that when you assemble the Earth out of chondrites, you've got slightly different gases being evolved from heating up all these materials that have assembled to form the Earth. Our calculations provide a natural explanation for getting this reducing atmosphere," said Fegley.

Schaefer presented the findings at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society, held Sept. 4-9 in Cambridge, England.

Schaefer and Fegley looked at different types of chondrites that earth and planetary scientists believe were instrumental in making the Earth. They used sophisticated computer codes for chemical equilibrium to figure out what happens when the minerals in the meteorites are heated up and react with each other. For example, when calcium carbonate is heated up and decomposed, it forms carbon dioxide gas.

"Different compounds in the chondritic Earth decompose when they're heated up, and they release gas that formed the earliest Earth atmosphere," Fegley said.

The Miller-Urey experiment featured an apparatus into which was placed a reducing gas atmosphere thought to exist on the early Earth. The mix was heated up and given an electrical charge and simple organic molecules were formed. While the experiment has been debated from the start, no one had done calculations to predict the early Earth atmosphere.

"I think these computations hadn't been done before because they're very difficult; we use a special code" said Fegley, whose work with Schaefer on the outgassing of Io, Jupiter's largest moon and the most volcanic body in the solar system, served as inspiration for the present early Earth atmosphere work.

NASA's Astrobiology Institute supported this work.

Go here to view the original at Washington University in St. Louis

- posted by Affenhänger @ 9/15/2005 04:46:00 AM 0 comments links to this post

 
Earth's core rotates faster than its crust, scientists say

CHAMPAIGN, Ill. — Scientists have ended a 9-year-old debate by proving that Earth’s core rotates faster than its surface, by about 0.3 to 0.5 degree per year.

"Extraordinary claims require extraordinary proof," said Xiaodong Song, a professor of geology at the University of Illinois at Urbana-Champaign and corresponding author of a paper to appear in the Aug. 26 issue of the journal Science. "We believe we have that proof."

Earth’s iron core consists of a solid inner core about 2,400 kilometers in diameter and a fluid outer core about 7,000 kilometers in diameter. The inner core plays an important role in the geodynamo that generates Earth’s magnetic field, and an electromagnetic torque from the geodynamo is thought to drive the inner core to rotate relative to the mantle and crust.

The first observational evidence for differential rotation was presented in 1996 by Song and Paul Richards, a seismologist at the Lamont-Doherty Earth Observatory of Columbia University. For the past nine years, some seismologists have suspected that flaws, or artifacts, in the data were responsible for the purported movement.

By comparing historical seismic waves traversing Earth’s fluid and solid cores, Song and his colleagues found compelling evidence for differential rotation of the solid inner core. The researchers reported observations of 17 sets of similar seismic waves – called waveform doublets – from earthquakes occurring in the South Sandwich Islands region off the coast of South America.

The doublets, which were recorded at up to 58 seismic stations in and near Alaska with a time separation of up to 35 years, allowed the researchers to detect temporal changes along the sampling paths.

"The similar seismic waves that passed through the inner core show systematic changes in travel times and wave shapes when the two events of the doublet are separated in time by several years," Song said. "The only plausible explanation is a motion of the inner core."

The most likely explanation for why the inner core is rotating at a different speed, Song said, is electromagnetic coupling. "The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current. The interaction of that electric current with the magnetic field causes the inner core to spin, like the armature in an electric motor."

The fluid outer core decouples the solid inner core’s movement from the mantle. Because the fluid outer core is not very viscous, frictional drag is small.

"Differential rotation is a fundamental dynamic process that goes to the heart of the origin of our planet and how it has evolved," Song said. "There is still much to learn about the inner Earth."

In addition to Song and Richards, co-authors are Illinois graduate students Yingchun Li and Xinlei Sun and Columbia graduate student Jian Zhang and research scientist Felix Waldhauser. The work was funded by the U.S. National Science Foundation and the Natural Science Foundation of China.

Go to News Bureau, University of Illinois at Urbana-Champaign to read the original

- posted by Affenhänger @ 9/08/2005 07:53:00 AM 0 comments links to this post

 
Study Reconciles Long-standing Contradiction Of Deep-earth Dynamics

Researchers at Columbia University's Lamont-Doherty Earth Observatory recently resolved a long-standing contradiction about the workings of the deep Earth. For years, many geochemists have argued that parts of the deep mantle remain unchanged since the formation of the Earth, whereas many geophysicists and geodynamicists have held that the entire mantle has been convecting (moving and mixing) over geological time.

Based on a synthesis of data on global oceanic magmatism, Cornelia Class and Steven L. Goldstein show that the evidence actually favors whole-mantle convection, with the deepest parts of the Earth affected by the tectonic processes that occur at the surface. Their study will appear in the August 25 issue of the journal Nature.

"For thirty years scientists have been debating whether there is a layer in the mantle that has remained unchanged since the formation of the Earth," said Class, a Doherty Associate Research Scientist. "The new on-line databases made it possible for the first time to reevaluate the geochemical arguments based on a complete synthesis of global data on oceanic basalts. We found that the strongest evidence previously put forth in favor of a layered mantle actually indicates the opposite is true."

The question of whether the Earth's interior operates on a "layered" or "whole-mantle" model is central to scientists' understanding of how the Earth loses its internal heat. The main process of heat loss occurs through melting of the mantle to form magma. If the layered model is correct, then a large portion of the deep earth never melts and never reaches the surface. Evaluations of seismic waves generated by earthquakes indicate that continental and oceanic plates sink all the way to the core-mantle boundary, an observation that supports whole-mantle convection. However, evidence from trace amounts of helium in lavas have been interpreted as requiring that the mantle is composed of layers that are isolated from each other.

When magma is erupted by volcanoes, helium and other gasses from the mantle are expelled to the atmosphere. Unlike other gases, the helium is so light that it is lost forever to space. As a result, the Earth's inventory of 3He, the light isotope of helium, is considered "primordial," dating from the time of the formation of the planet. Indications of a high proportion of primordial helium in ocean island lavas, like those found in Hawaii, have been taken as evidence for a layer in the deep mantle that has never been melted and, hence, never degassed.

"This result adds to growing evidence that most of Earth's mantle has been subject to the same forces that drive the movements of Earth's crust," said Sonia Esperanca, a Program Director in the National Science Foundation's Division of Earth Sciences, which funded the research.

Class and Goldstein's re-evaluation of this concept of the inner Earth was based on their work with two new databases that for the first time compile all of the published data on the geochemistry of oceanic volcanism around the world: the Petrological Database of Ocean Floor Basalts (PetDB, based at Lamont) and Geochemistry of Rocks from the Oceans and Continents (GEOROC).

It has long been known that the upper mantle sources of basalt found at mid-ocean ridges, formed by sea floor spreading, have been previously melted to form oceanic and continental crust. The new global data synthesis demonstrates that the ocean island lavas that are chemically most like mid-ocean ridge basalt also contain the highest primordial helium signal. As a result, this helium signal actually indicates previous processing by plate tectonics, rather than a primordial mantle source. Class and Goldstein conclude that helium must be degassed inefficiently to the atmosphere through volcanic processes and enough remains in the mantle during melting to give the false impression that the deep mantle is primordial.

"Our results mean we can dispense once and for all with the argument that the helium data require a primordial layer in the mantle, whose existence has been difficult to reconcile with the rest of what we know about how the Earth works," said Goldstein, a professor of Earth and Environmental Sciences at Columbia University and member of the Lamont-Doherty senior staff. "The implications of our work will be hotly debated, but I expect these new observations to change the way we view deep-Earth dynamics."

###

The study was funded by the National Science Foundation.

The Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, is one of the world's leading research centers seeking fundamental knowledge about the origin, evolution and future of the natural world. More than 200 research scientists study the planet from its deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean. From global climate change to earthquakes, volcanoes, nonrenewable resources, environmental hazards and beyond, Observatory scientists provide a rational basis for the difficult choices facing humankind in the planet's stewardship. For more information, visit www.ldeo.columbia.edu

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- posted by Affenhänger @ 9/06/2005 08:53:00 PM 0 comments links to this post