Featured Research

from universities, journals, and other organizations

Fingerprinting Slow Earthquakes And How They Relate To The Big One

Date:
April 30, 2009
Source:
Carnegie Institution
Summary:
The most powerful earthquakes happen at the junction of two converging tectonic plates, where one plate is sliding (or subducting) beneath the other. Now scientists have found that an anomalous layer at the top of a subducting plate coincides with the locations of slow earthquakes and non-volcanic tremors. Such a layer in similar settings elsewhere could point to other regions of slow quakes.

A map of tectonic plates that make up the Earth's crust. Note how most earthquakes occur at plate boundaries, as the plates grind against each other to drive faults and generate earthquakes.
Credit: Image courtesy of USGS

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 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 research is published in the April 24th issue of Science.

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.


Story Source:

The above story is based on materials provided by Carnegie Institution. Note: Materials may be edited for content and length.


Journal Reference:

  1. Teh-Ru Alex Song, Donald. V. Helmberger, Michael R. Brudzinski, Robert W. Clayton, Paul Davis, Xyoli Pιrez-Campos, and Shri K. Singh. Subducting Slab Ultra-Slow Velocity Layer Coincident with Silent Earthquakes in Southern Mexico. Science, 2009; 324 (5926): 502-506 DOI: 10.1126/science.1167595

Cite This Page:

Carnegie Institution. "Fingerprinting Slow Earthquakes And How They Relate To The Big One." ScienceDaily. ScienceDaily, 30 April 2009. <www.sciencedaily.com/releases/2009/04/090423142322.htm>.
Carnegie Institution. (2009, April 30). Fingerprinting Slow Earthquakes And How They Relate To The Big One. ScienceDaily. Retrieved September 23, 2014 from www.sciencedaily.com/releases/2009/04/090423142322.htm
Carnegie Institution. "Fingerprinting Slow Earthquakes And How They Relate To The Big One." ScienceDaily. www.sciencedaily.com/releases/2009/04/090423142322.htm (accessed September 23, 2014).

Share This



More Earth & Climate News

Tuesday, September 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Hundreds of Thousands Hit NYC Streets to Protest Climate Change

Hundreds of Thousands Hit NYC Streets to Protest Climate Change

AFP (Sep. 22, 2014) — Celebrities, political leaders and the masses rallied in New York and across the globe demanding urgent action on climate change, with organizers saying 600,000 people hit the streets. Duration: 01:19 Video provided by AFP
Powered by NewsLook.com
Raw: Protesters Stage Wall Street Climate Sit-in

Raw: Protesters Stage Wall Street Climate Sit-in

AP (Sep. 22, 2014) — A day after over 100,000 people marched against climate change, more than 1,000 activists blocked parts of Manhattan's financial district. Over 100 people, including a person wearing a white polar bear suit, were arrested Monday night. (Sept. 22) Video provided by AP
Powered by NewsLook.com
French FM Urges 'powerful' Response to Global Warming

French FM Urges 'powerful' Response to Global Warming

AFP (Sep. 22, 2014) — French Foreign Minister Laurent Fabius on Monday warned about the potential "catastrophe" if global warming was not dealt with in a "powerful" way. Duration: 01:08 Video provided by AFP
Powered by NewsLook.com
Ongoing Drought, Fighting Put Somalia at Risk of Famine

Ongoing Drought, Fighting Put Somalia at Risk of Famine

AFP (Sep. 22, 2014) — After a year of poor rains and heavy fighting Somalia is again at risk of famine, just three years after food shortages killed 260,000 people. Duration: 01:10 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins