Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tiny clays curb big earthquakes

25.06.2010
California's San Andreas fault is notorious for repeatedly generating major earthquakes and for being on the brink of producing the next "big one" in a heavily populated area. But the famously violent fault also has quieter sections, where rocks easily slide against each other without giving rise to damaging quakes.

The relatively smooth movement, called creep, happens because the fault creates its own lubricants---slippery clays that form ultra-thin coatings on rock fragments, geologist Ben van der Pluijm and colleagues at the University of Michigan and Germany's Ernst-Moritz-Arndt Universität Institut für Geographie und Geologie report in the July issue of Geology.

The question of why some fault zones creep slowly and steadily while others lock for a time and then shift suddenly and violently, spawning earthquakes, has long puzzled scientists. Some have speculated that fluids facilitate slippage, while others have focused on serpentine---a greenish material that can alter to slippery talc.

But when van der Pluijm and colleagues analyzed samples of rock from an actively creeping segment that was brought up from a depth of two miles below the surface as part of the San Andreas Fault Observatory at Depth (SAFOD) project, they found very little talc. Instead, they found that fractured rock surfaces were coated with a thin layer of smectitic clay, less than 100 nanometers thick, that acts something like grease on ball bearings.

"For a long time, people thought you needed a lot of lubricant for creep to occur," said van der Pluijm, who is the Bruce R. Clark Collegiate Professor of Geology and Professor of the Environment. "What we can show is that you don't really need a lot; it just needs to be in the right place. It's a bit like real estate: location, location, location." The nanocoatings occur on the interfaces of broken-up bits of rock in exactly the places where they affect the fault's "weakness"---how easily it moves.

The technique of argon dating provided key evidence, when the researchers determined that these clays, found only in fault rock, formed relatively recently.

"The clays are growing in the fault zone, and the fault is coating its own pieces of fragmented rock," van der Pluijm said. "At some point there's enough coating that it begins to drive the behavior of the fault, and creeping kicks in."

If the fault is greasing itself, then why do earthquakes still occur?

"The problem is that the fault doesn't always move at strands where the coating sits," van der Pluijm said. The San Andreas fault is actually a network of faults, with new strands being added all the time. Because it takes some time for the slick nanocoatings to develop in a new strand, the unlubricated, new strand "gets stuck" for a time and then shifts in a violent spasm.

Although the samples obtained through SAFOD are from a depth of only about two miles, van der Pluijm and colleagues think it's likely the clay nanocoatings also are forming and driving fault behavior at greater depths. What's more, analyses of older, inactive strands suggest that the coatings have been facilitating creep for the millions of years of fault activity.

The SAFOD project, which is establishing the world's first underground earthquake observatory, is a major research component of EarthScope, an ambitious, $197-million federal program to investigate the forces that shaped the North American continent and the processes controlling earthquakes, volcanoes and other geological activity.

Van der Pluijm's coauthors on the paper are U-M assistant research scientist Anja Schleicher and Professor Laurence Warr of Ernst-Moritz-Arndt Universität Institut für Geographie und Geologie. The researchers received funding from the National Science Foundation and the Deutsche Forschungsgemeinschaft.

More information:

Ben van der Pluijm: http://www.ns.umich.edu/htdocs/public/experts/ExpDisplay.php?ExpID=781

San Andreas Fault Observatory at Depth: http://www.earthscope.org/observatories/safod

EarthScope: http://www.earthscope.org

Geology: http://geology.gsapubs.org/

National Science Foundation: http://www.nsf.gov/

Deutsche Forschungsgemeinschaft: http://www.dfg.de/en/index.jsp

Nancy Ross-Flanigan | EurekAlert!
Further information:
http://www.umich.edu

More articles from Earth Sciences:

nachricht PR of MCC: Carbon removal from atmosphere unavoidable for 1.5 degree target
22.05.2018 | Mercator Research Institute on Global Commons and Climate Change (MCC) gGmbH

nachricht Monitoring lava lake levels in Congo volcano
16.05.2018 | Seismological Society of America

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Designer cells: artificial enzyme can activate a gene switch

22.05.2018 | Life Sciences

PR of MCC: Carbon removal from atmosphere unavoidable for 1.5 degree target

22.05.2018 | Earth Sciences

Achema 2018: New camera system monitors distillation and helps save energy

22.05.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>