Expert warns of another quake in Andaman region

[Mod]

Expert warns of another quake in Andaman region

 Saowanee Nimpanpayungwong
 The Nation
 
BANGKOK: A fierce earthquake from the Nicobar Islands could strike over Songkran, sending a tsunami crashing into the Andaman Coast, an expert warned yesterday after finding that the 8.6magnitude Sumatran tremor three days ago was exceptionally deep.
 
"Whenever there is a quake rooted in the [Earth's] mantle, a following quake will be likely in the next few days," said Professor Thanawat Jaruphongsakul, a senior seismologist at Chulalongkorn University.
 
Fear of another devastating tsunami panicked Thailand and Southeast Asia on Wednesday.
 
An underwater quake, with its epicentre at the Nicobar Islands, about 150 kilometres north of Aceh on Sumatra, would affect six coastal provinces of Thailand on the Andaman Sea, especially Ranong, which lies closest to a fault line connecting with the Nicobar Islands, he said.
 
The quakes on Wednesday originated from mantle level crust, 20 kilometres below the Earth's surface, which is regarded as a layer that would cause very high magnitude tremblers.
 
The quake that hit Japan in March came from a shallower layer, so it would take up to 100-150 years for the next quake. However Wednesday's quakes, with their epicentre at Aceh, followed just eight years after the massive one that triggered a continent wide tsunami that killed hundreds of thousands of people in many countries, he said.
 
"Why did Wednesday's quakes emerge just eight years afterwards? This is new to most seismologists and geologists, who are unfamiliar with quakes with depth rooting to the mantle layer," he said.
 
Seismologists were closely watching and cautiously studying the 9.0 quake that devastated Sendai in Japan on March 11 last year. The first tremor on March 9 was recorded at 7.3 on the Richter scale. That one was understood by seismologists as the main shock, but there were two aftershocks on an even greater scale at 9.0 on March 11 that followed, he said.
 
The tsunamis created on Wednesday were not powerful or harmfully high because the quake was the horizontal dipslide type. But a mantle based quake at an island with active underwater volcanoes located north of the Nicobar Islands would probably be a vertical strikeslip type, which would directly impact the six Thai coastal provinces, and possibly deluge them with tsunamis, he added.
 
Professor Michio Hashzume, a well known Japanese seismologist, said Wednesday's quakes were a new type known to have started in the mantle. It was difficult to tell whether a new quake would follow within a few days, like the Sendai quakes, which were similar to Wednesday's quakes. Then there was a 7.3, followed by a 9.0 two days later.
 
If there are quakes near the Nicobar Islands, they may cause huge collapses in the seabed and outer crust. The seabed may rise and form new islands, he said.
 
The Nation 2012-04-13

[isanbirder]

Of course we all hope not.  It's one of those predictions where, if it's right, we say how clever he is, but if it's wrong, we're so relieved that we don't blame him for scaring us.

[gotlost]

Sumatra quake reveals new seismic information By Peter Shadbolt, CNN
April 14, 2012 -- Updated 0359 GMT (1159 HKT)
The latest Indonesian quake was the largest 'strike-slip' earthquake ever recordedSTORY 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.