Featured Research

from universities, journals, and other organizations

Study reveals complex rupture process in surprising 2012 Sumatra quake

Date:
September 26, 2012
Source:
University of California - Santa Cruz
Summary:
The massive earthquake that struck under the Indian Ocean southwest of Sumatra on April 11, 2012, came as a surprise to seismologists and left them scrambling to figure out exactly what had happened. Analysis of the seismic waves generated during the event has now revealed a complicated faulting process unlike anything seen before.

The diagram above shows the complex network of faults that ruptured during the magnitude 8.7 earthquake and 8.2 aftershock in the Indo-Australian Plate.
Credit: Image courtesy of Thorne Lay

The massive earthquake that struck under the Indian Ocean southwest of Sumatra on April 11, 2012, came as a surprise to seismologists and left them scrambling to figure out exactly what had happened. Analysis of the seismic waves generated during the event has now revealed a complicated faulting process unlike anything seen before.

"Nobody was anticipating an earthquake of this size and type, and the complexity of the faulting surprised everybody I've spoken to about this," said Thorne Lay, professor of Earth and planetary sciences at the University of California, Santa Cruz.

Lay, UCSC graduate student Han Yue, and University of Utah geologist Keith Koper have published a detailed analysis of the fault ruptures in Nature (published online Sept. 26). Another team reported a similar pattern of faults in a recent paper in Science, but without the quantitative details provided in the new paper, which is accompanied by two other papers addressing different aspects of this unusual earthquake.

During the magnitude 8.7 earthquake, the Indo-Australian plate--a major tectonic plate that includes Australia and the surrounding ocean--ruptured over a complex network of at least four faults lying at right angles to one another. According to Lay, the energy released on each fault individually was about magnitude 8, adding up to a total event magnitude of 8.7 (a point higher than the 8.6 value initially reported for the quake). The initial shock was followed two hours later by a magnitude 8.2 aftershock on yet another fault to the south.

Most great earthquakes (magnitude 8 and above) occur at the edges of plates in subduction zones, where one plate is diving under the adjoining plate and motion along the fault causes vertical displacement of the surface. The April earthquake involved horizontal ("strike-slip") motion on a series of faults in the middle of the plate. It was both the largest strike-slip earthquake and the largest intraplate earthquake ever recorded. The faults broke through the upper part of the plate and appear to have slipped as much as 35 to 40 meters during the quake, Lay said.

"What we're seeing here is the Indo-Australian plate fragmenting into two separate plates," he said. "We've seen local fragmentation on a small scale, but this is an unprecedented opportunity for us to witness it on the scale of a giant tectonic plate."

The fragmentation is caused by stresses within the plate resulting from its collision with Asia in the northwest, which slows down the western part of the plate, while the other side continues moving steadily north, sliding under Sumatra to the northeast. The Indian subplate will eventually separate from the Australian subplate, but exactly where the plate boundary will form is not yet clear, Lay said.

He added that the process of forming a new plate boundary will take millions of years and is likely to require hundreds if not thousands of earthquakes like the one in April. "This was a huge earthquake, but it's going to happen again and again to make a through-going fracture that separates the plates," he said.

The good news is that this is not a particularly hazardous type of earthquake, because the horizontal slip does not displace the water above the fault enough to generate a big tsunami. "It doesn't present a lot of societal hazard, so that's good," Lay said. "It is humbling, though, that this event was well beyond anything we could anticipate."

This research was funded by the National Science Foundation.


Story Source:

The above story is based on materials provided by University of California - Santa Cruz. The original article was written by Tim Stephens. Note: Materials may be edited for content and length.


Journal Reference:

  1. Han Yue, Thorne Lay, Keith D. Koper. En ιchelon and orthogonal fault ruptures of the 11 April 2012 great intraplate earthquakes. Nature, 2012; DOI: 10.1038/nature11492

Cite This Page:

University of California - Santa Cruz. "Study reveals complex rupture process in surprising 2012 Sumatra quake." ScienceDaily. ScienceDaily, 26 September 2012. <www.sciencedaily.com/releases/2012/09/120926133101.htm>.
University of California - Santa Cruz. (2012, September 26). Study reveals complex rupture process in surprising 2012 Sumatra quake. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2012/09/120926133101.htm
University of California - Santa Cruz. "Study reveals complex rupture process in surprising 2012 Sumatra quake." ScienceDaily. www.sciencedaily.com/releases/2012/09/120926133101.htm (accessed July 31, 2014).

Share This




More Earth & Climate News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) — Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Florida Panther Rebound Upsets Ranchers

Florida Panther Rebound Upsets Ranchers

AP (July 31, 2014) — With Florida's panther population rebounding, some ranchers complain the protected predators are once again killing their calves. (July 31) Video provided by AP
Powered by NewsLook.com
Big Waves In Arctic Ocean Threaten Polar Ice

Big Waves In Arctic Ocean Threaten Polar Ice

Newsy (July 30, 2014) — Big waves in parts of the Arctic Ocean are unprecedented, mainly because they used to be covered in ice. Video provided by Newsy
Powered by NewsLook.com
Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) — Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) 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:

More Coverage


Magnitude-8.7 Quake Was Part of Crustal Plate Breakup

Sep. 26, 2012 — Seismologists have known for years that the Indo-Australian plate of Earth's crust is slowly breaking apart, but they saw it in action last April when at least four faults broke in a ... read more
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