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Subject: [SPAM] STLtoday article: Shallower waters may have helped to stave off tsunami from [EMAIL PROTECTED]
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Shallower waters may have helped to stave off tsunami By THE ASSOCIATED PRESS
Below is the link to the story. http://www.stltoday.com/stltoday/news/stories.nsf/world/story/A36DBD6D4FCB2B2D86256FD500189464?OpenDocument
Here is the story.
[<B>]Ocean floor also heaved[</B>] [<B>]across smaller area in[</B>] [<B>]latest quake, expert says[</B>]
TOKYO - Why was there no tsunami this time?
After the magnitude-8.7 earthquake off Indonesia on Monday night, warnings blared along coastlines in Thailand, India and Sri Lanka, and frightened residents fled inland for fear of a deadly tsunami like the one in December.
But the big waves never came, and scientists say differences in the ocean topography and the movement of the Earth's crust are the reasons.
Keiji Doi of Tokyo University's Earthquake Research Institute said the size of a tsunami essentially depends on two factors: the volume of sea water above where the quake occurs and the extent of the movement.
"This quake occurred in much shallower waters because the area is a continuation of the Sumatra land mass, so less water was displaced," Doi said.
The epicenter of Monday's quake was about 56 miles south of Simeulue Island, off Sumatra's western coast.
Doi said waters there are probably 330 to 660 feet deep, compared with the oceans above the Dec. 26 temblor off Sumatra's Aceh province, which were about 10 times that depth.
He also said the ocean floor heaved across a much larger area in December - about 92,700 square miles compared with 11,600 square miles on Monday.
"The amount of water impacted was on a completely different scale," Doi said.
The quake in December spawned killer waves that hit 11 countries, leaving more than 280,000 dead or missing. Waves more than 100-feet high were observed along Sumatra's west coast, according to the U.S. Geological Survey.
This week's quake barely caused a ripple. The highest wave recorded by Japan's Meteorological Agency was off Salalah, Oman, and measured a mere 12 inches.
Hiroshi Ueno, of the Earthquake and Tsunami Observations Division of Japan's Meteorological Agency, said the depth at which displacement in the earth's crust occurs during a quake also can affect a tsunami's size.
According to the U.S. Geological Survey, both December's and Monday's quakes had epicenters about 19 miles under the seabed.
But displacement along a fault line during an earthquake can be uneven.
The point at which the greatest shift occurred Monday was relatively deep underground, whereas in December, a large portion of the seabed jolted almost uniformly along the fault line, Ueno said.
Both Doi and Ueno said their explanations were educated guesses based on current data and further studies are planned.
"It just shows how difficult it is to predict tsunamis," Doi said. "It's not an exact science, especially right after the fact, when you don't have this kind of data."
[<B>]Rewrite the records?[</B>]
Experts in Denver, meanwhile, say aftershocks still are rattling Sumatra three months after the December quake.
Some researchers have determined that the Dec. 26 quake was even more powerful than previously believed and say the record books should be rewritten to reflect this new, even-greater status. But other scientists say their findings are premature.
A study by seismologists at Northwestern University increases the intensity of the December earthquake from a magnitude 9.0 to a whopping magnitude 9.3. That's about three times more powerful than initial estimates.
But the U.S. Geological Survey - the world's record keeper for all things seismic - isn't buying the argument. Officials there say they are awaiting several other studies before they officially recalibrate the earthquake's magnitude.
If the Northwestern calculations are confirmed, it would make the undersea Sumatra-Andaman earthquake the second most powerful ever recorded.
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