Featured Research

from universities, journals, and other organizations

Sumatra Earthquake Three Times Larger Than Originally Thought

Date:
February 12, 2005
Source:
Northwestern University
Summary:
Northwestern University seismologists have determined that the Dec. 26 Sumatra earthquake that set off a deadly tsunami throughout the Indian Ocean was three times larger than originally thought, making it the second largest earthquake ever instrumentally recorded and explaining why the tsunami was so destructive.

Map comparing the aftershock zone to the minimum area of fast slip previously recognized and the much larger area of slow slip shown by analysis of normal mode data.
Credit: Courtesy of Northwestern University

EVANSTON, Ill. --- Northwestern University seismologists have determined that the Dec. 26 Sumatra earthquake that set off a deadly tsunami throughout the Indian Ocean was three times larger than originally thought, making it the second largest earthquake ever instrumentally recorded and explaining why the tsunami was so destructive.

By analyzing seismograms from the earthquake, Seth Stein and Emile Okal, both professors of geological sciences in Northwestern's Weinberg College of Arts and Sciences, calculated that the earthquake's magnitude measured 9.3, not 9.0, and thus was three times larger. These results have implications for why Sri Lanka suffered such a great impact and also indicate that the chances of similar large tsumanis occurring in the same area are reduced.

"The rupture zone was much larger than previously thought," said Stein. "The initial calculations that it was a 9.0 earthquake did not take into account what we call slow slip, where the fault, delineated by aftershocks, shifted more slowly. The additional energy released by slow slip along the 1,200-kilometer long fault played a key role in generating the devastating tsunami."

The large tsunami amplitudes that occurred in Sri Lanka and India, said tsunami expert Okal, result from rupture on the northern, north-trending segment of the fault -- the area of slow slip -- because tsunami amplitudes are largest perpendicular to the fault.

Because the entire rupture zone slipped (both fast and slow slip fault areas), strain accumulated from subduction of the Indian plate beneath the Burma microplate has been released, leaving no immediate danger of a comparable ocean-wide tsunami being generated on this segment of the plate boundary. However, the danger of a local tsunami due to a powerful aftershock or a large tsunami resulting from a great earthquake on segments to the south remains.

The analysis technique used by Stein and Okal to extract these data from the earth's longest period vibrations (normal modes) relied on results developed by them and colleague Robert Geller (now at the University of Tokyo) in their graduate studies almost 30 years ago. However, because such gigantic earthquakes are rare, these methods had been essentially unused until records of the Sumatra earthquake on modern seismometers became available.

The largest earthquake ever recorded, which measured 9.5, was in Chile on May 22, 1960.

Additional information on this research can be found at http://www.earth.northwestern.edu/people/seth/research/sumatra2.html.


Story Source:

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


Cite This Page:

Northwestern University. "Sumatra Earthquake Three Times Larger Than Originally Thought." ScienceDaily. ScienceDaily, 12 February 2005. <www.sciencedaily.com/releases/2005/02/050211094339.htm>.
Northwestern University. (2005, February 12). Sumatra Earthquake Three Times Larger Than Originally Thought. ScienceDaily. Retrieved September 20, 2014 from www.sciencedaily.com/releases/2005/02/050211094339.htm
Northwestern University. "Sumatra Earthquake Three Times Larger Than Originally Thought." ScienceDaily. www.sciencedaily.com/releases/2005/02/050211094339.htm (accessed September 20, 2014).

Share This



More Earth & Climate News

Saturday, September 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Climate Change Rally Held in India Ahead of UN Summit

Climate Change Rally Held in India Ahead of UN Summit

AFP (Sep. 20, 2014) Some 125 world leaders are expected to commit to action on climate change at a UN summit Tuesday called to inject momentum in struggling efforts to tackle global warming. Duration: 00:41 Video provided by AFP
Powered by NewsLook.com
New Music With Recycled Instruments at Colombia Fest

New Music With Recycled Instruments at Colombia Fest

AFP (Sep. 19, 2014) Jars, bottles, caps and even a pizza box, recovered from the trash, were the elements used by four musical groups at the "RSFEST2014 Sonorities Recycling Festival", in Colombian city of Cali. Duration: 00:49 Video provided by AFP
Powered by NewsLook.com
Raw: Wildfires in CA Burn Forest Asunder

Raw: Wildfires in CA Burn Forest Asunder

AP (Sep. 18, 2014) An out-of-control Northern California wildfire has nearly 2,800 people from their homes as it continues to grow, authorities said Thursday. Authorities said a man has been arrested on suspicion of arson for starting the fire on Saturday. (Sept. 18) Video provided by AP
Powered by NewsLook.com
Raw: Elephant Undergoes Surgery in Tbilisi Zoo

Raw: Elephant Undergoes Surgery in Tbilisi Zoo

AP (Sep. 18, 2014) Grand the elephant has successfully undergone surgery to remove a portion of infected tusk at Tbilisi Zoo in Georgia. British veterinary surgeons used an electric drill to extract the infected piece. (Sept. 18) Video provided by AP
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:
from the past week

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