Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fingerprinting slow earthquakes

24.04.2009
The most powerful earthquakes happen at the junction of two converging tectonic plates, where one plate is sliding (or subducting) beneath the other.

Now a team of researchers, led by Teh-Ru Alex Song of the Carnegie Institution's Department of Terrestrial Magnetism, has found that an anomalous layer at the top of a subducting plate coincides with the locations of slow earthquakes and non-volcanic tremors.

The presence of such a layer in similar settings elsewhere could point to other regions of slow quakes. Slow earthquakes, also called silent earthquakes, take days, weeks, or even months to release pent-up energy instead of seconds or minutes as in normal earthquakes. The research is published in the April 24th issue of Science.

The scientists analyzed 20 years of seismic data for southern Mexico, where the Cocos plate is slipping beneath the North American plate. "We can tell a lot about the material inside the Earth by the speed, strength, and interferences of different seismic waves," explained Song. "Typically, P-waves are the fastest, followed by scattered waves associated with variations in seismic wave speed within the medium. We used local observations recorded within 100 to 150 miles to map the structures at the top of the subducting plate."

From observations and modeling, the researchers found that 30 events had similar waveforms and thus provided reinforcing information on structural details in the source region. In particular, they found a layer on top of the subducted plate where the speed of S-waves—which do not travel through liquids and are slower than P-waves—was some 30% to 50% slower than typical water-laden oceanic crust. The anomalous layer, dubbed the ultra-slow-velocity layer by the researchers, is found at depths of 15 to 30 miles (25 to 50 kilometers), somewhat deeper than the portion of the plate interface zone that is strongly coupled and is the site of great earthquakes in this region. The spatial distribution of such a structure is also confirmed by observations recorded by stations located more than 3,000 miles away in Canada.

The scientists also examined the locations where slow earthquakes and non-volcanic tremors have occurred. They found that slow earthquake areas and the ultra-slow-velocity layers cluster together, and that regions of non-volcanic tremors are adjacent to those clusters.

But what is this layer and what does it have to do with these seismic events? Song and team believe that it may be subducted oceanic crust at unusually high levels of water saturation. The cause of such anomalously high pore pressures is unknown, but a clue might come from the fact that non-volcanic tremors are concentrated in areas with temperatures around 840°F (450°C). The researchers think that at such temperature and under ambient pressures a combination of fluid release and reduction in permeability may give rise both to the high pore pressures and the stimulation of tremor activities.

"The ultra-slow-velocity layer may be the fingerprint that shows us where these slow quakes are active elsewhere in the world," remarked Song. "It is extremely important to learn more about slow quakes and how they are temporally and spatially associated with more powerful and destructive earthquakes. Mapping these structures is a first step toward this goal, and the study provides observational data that can be used in numerical simulations on stress interactions between slow earthquakes and megaearthquakes."

The work is supported by the Caltech Tectonic Observatory (funded by the Gordon and Betty Moore Foundation), the Center of Embedded Network Systems (CENS) at UCLA, the National Science Foundation, and Carnegie.

The Carnegie Institution for Science (www.CIW.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Teh-Ru Alex Song | EurekAlert!
Further information:
http://www.ciw.edu

More articles from Earth Sciences:

nachricht Arctic melt ponds form when meltwater clogs ice pores
24.01.2017 | University of Utah

nachricht New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Scientists spin artificial silk from whey protein

X-ray study throws light on key process for production

A Swedish-German team of researchers has cleared up a key process for the artificial production of silk. With the help of the intense X-rays from DESY's...

Im Focus: Quantum optical sensor for the first time tested in space – with a laser system from Berlin

For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.

According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Breaking the optical bandwidth record of stable pulsed lasers

24.01.2017 | Physics and Astronomy

Choreographing the microRNA-target dance

24.01.2017 | Life Sciences

Spanish scientists create a 3-D bioprinter to print human skin

24.01.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>