Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Brown Grad Student’s Seismic Study Shakes Up Plate Tectonics

29.07.2005


Where even rock is weaker - Between 90 and 110 kilometers below ground, Earth’s hard shell – the lithosphere – meets the more pliable asthenosphere. The boundary between the two layers is no more than 11 kilometers thick, according to a new study.


Earth’s cool, rigid upper layer, known as the lithosphere, rides on top of its warmer, more pliable neighbor, the asthenosphere, as a series of massive plates. Plates continuously shift and break, triggering earthquakes, sparking volcanic eruptions, sculpting mountains and carving trenches under the sea.

But what, exactly, divides the lithosphere and the asthenosphere? In the latest issue of Nature, a trio of geophysicists from Brown University and the Massachusetts Institute of Technology publish research that sheds new light on the nature of the boundary between these rocky regions.

Lead author Catherine Rychert, a 26-year-old graduate student in Brown’s Department of Geological Sciences, found a sharp dividing line between the lithosphere and the asthenosphere, according to data culled from seismic sensors sprinkled across the northeastern United States and southeastern Canada. Rychert and colleagues discovered that sound waves recorded by the sensors slow considerably about 90 to 110 kilometers below ground – a sign that the rock is getting weaker and that the lithosphere is giving way to the asthenosphere. Within in a distance of a mere 11 kilometers – roughly 7 miles or less – the transition is complete.



This evidence runs contrary to the prevailing notion that the lithosphere-asthenosphere transition is a gradual one. It also points up the fact that temperature alone cannot define the boundary. Rychert said that water or a small amount of partly molten rock must also be present in the asthenosphere to cause such an abrupt change in the mechanical strength of the rock.

“These findings will be controversial because they run counter to what some scientists believe is true,” Rychert said. “Regardless, they’re pretty cool. We know something new, literally, about the earth under our feet.”

To conduct the study, Rychert gathered seismic data from hundreds of earthquakes recorded during more than five years at six government-operated or university-run research stations in Canada, New Hampshire, Massachusetts, New York and Pennsylvania. She modeled and analyzed the data with the assistance of Karen Fischer, the Royce Family Professor of Teaching Excellence and professor of geological sciences at Brown, and Stéphane Rondenay, the Kerr-McGee Assistant Professor of Seismology at MIT and a former postdoctoral research fellow at Brown. The project took three years to complete.

“We initially were very surprised by the sharpness of the lithosphere-asthenosphere boundary indicated by the data,” said Fischer, “and so I challenged Kate to prove that such a rapid transition is definitively required. All of her careful modeling has now paid off with a result that makes a fundamental contribution to our understanding of the Earth’s lithosphere.”

The Geophysics Program at the National Science Foundation funded the work.

Wendy Lawton | EurekAlert!
Further information:
http://www.brown.edu

More articles from Earth Sciences:

nachricht NASA's AIM observes early noctilucent ice clouds over Antarctica
05.12.2016 | NASA/Goddard Space Flight Center

nachricht GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NASA's AIM observes early noctilucent ice clouds over Antarctica

05.12.2016 | Earth Sciences

Shape matters when light meets atom

05.12.2016 | Physics and Astronomy

Researchers uncover protein-based “cancer signature”

05.12.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>