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Sumatra quake reveals new seismic information

By Peter Shadbolt, CNN
updated 11:59 PM EDT, Fri April 13, 2012
The latest Indonesian quake was the largest 'strike-slip' earthquake ever recorded
The latest Indonesian quake was the largest 'strike-slip' earthquake ever recorded
STORY HIGHLIGHTS
  • Sumatra quake the largest of its type ever recorded
  • The 8.6 scale strike-slip earthquake has given new insights for seismologists
  • The quake was so large it extended beyond the Earth's crust to the mantle
  • He said the quake has increased the stress on the plates in the area

(CNN) -- The undersea earthquake off the Indonesian island of Sumatra on Wednesday was the largest earthquake of its type ever recorded and has increased the risk of more powerful quakes in the region, a leading expert has said.

Director of the Earth Observatory of Singapore, Kerry Sieh, told CNN that the 8.6 Richter scale undersea earthquake was the largest "strike-slip" quake - steep structures where the two sides of the fault slip horizontally past each other - ever recorded.

"Before that we thought that 8.1 was as big as they get, but this 8.6 quake was phenomenal," Sieh said. "It has been absolutely jaw-dropping and has caused a lot of foment among seismologists."

He said the quake had provided two new insights for seismologists.

Firstly, that strike-slip earthquakes, which are normally not as powerful as mega-thrust quakes where one plate runs underneath another, could be this powerful. Secondly, that big earthquakes of this type could run as deep as the Earth's mantle, the viscous layer beneath the Earth's crust.

"We are learning details about the nature of the ruptures," he said. "What are the fits and starts of the fault? How does the fault break?"

Likening the tectonic plates to a group of 10 men holding onto an elephant with a rope, he said that pressure on the plates becomes greater as the struggle becomes unequal.

"Finally, when one of the guys slips and can't hold the rope what happens is that the nine other guys are holding his 10%, so they have to add 10% more effort to hold on," he said, adding that when a further man falls the remaining eight have an extra 20% of the force to contend with.

"Eventually what you have is a cascade of failures and the last guy has to let go and the tectonics win and the fault moves," Sieh said. "What we had in Sumatra between 2004 and 2007 was pop! Pop! Pop! Three great earthquakes; 9.2, 8.7, 8.4."

He said that Wednesday's earthquake was likely to have increased the stress on the plate boundaries near Aceh, increasing the risks of another major earthquake in the same area as the 2004 disaster.

"There's still one or two patches left to go," Sieh said.

He said the past 10 years had been particularly seismically active, providing invaluable information to seismologists.

"We've really seen a revolution in our understanding of earthquakes in the last 10 years because of these earthquakes," he said, adding that new technology and the speed with which information was shared had changed the landscape in understanding earthquakes.

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