Scientists Foresee Giant Earthquakes Off Sumatra

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Aron Meltzner next to a dead coral after uplift from the Sept. 2007 earthquake. i

Geologist Aron Meltzner stands next to a coral micro-atoll on Mega island. Science hide caption

itoggle caption Science
Aron Meltzner next to a dead coral after uplift from the Sept. 2007 earthquake.

Geologist Aron Meltzner stands next to a coral micro-atoll on Mega island. When earthquakes push the seafloor upward, lowering local sea level, the corals can't grow upward and instead grow outward.

Science
The Bulasat site rose during the earthquakes of September 2007. i

The Bulasat site (above) rose nearly 29 inches during the earthquakes of September 2007. Science hide caption

itoggle caption Science
The Bulasat site rose during the earthquakes of September 2007.

The Bulasat site (above) rose nearly 29 inches during the earthquakes of September 2007. In the foreground there are ancient corals that died during previous uplifts in about 1350 and 1600.

Science
A dead reef that was killed by an earthquake off the coast of Sumatra. i

A recently dead reef that was killed by uplift during the magnitude 8.4 earthquake in September 2007. Science hide caption

itoggle caption Science
A dead reef that was killed by an earthquake off the coast of Sumatra.

A recently dead reef that was killed by uplift during the magnitude 8.4 earthquake in September 2007.

Science
A cross section of a coral shows the rise in sea level. i

Like tree trunks, corals have annual growth rings. Science hide caption

itoggle caption Science
A cross section of a coral shows the rise in sea level.

Like tree trunks, corals have annual growth rings. A cross section of a coral shows the progressive rise in sea level in the decades prior to death of the coral.

Science

Scientists who have been studying earthquakes in the eastern Indian Ocean say they've got new evidence that a huge earthquake could strike there in the next few decades, and perhaps create a giant tsunami.

In 2004, a magnitude 9.1 quake struck along the Sunda trench, a fault that runs parallel to the Indonesian island of Sumatra. Within the next several hours, a tsunami swept across the Indian Ocean and killed some 225,000 people.

Scientists at the California Institute of Technology and in Indonesia have now figured out how to map the frequency of big quakes in this region — by measuring growth patterns in coral outgrowths called "micro-atolls." When seismic activity raises and lowers the seafloor, coral reefs are sometimes pushed up out of the water. When exposed to air, the coral top stops growing, but the sides keep growing outward. The result, says Caltech geologist Aron Meltzner, "looks kind of like a sombrero" a few yards across.

By measuring growth patterns in these micro-atolls, Meltzner and his colleagues discovered a cycle of earthquake activity.

"It's basically this pattern of a century or so of no earthquakes," he says, "and then a cluster of moderate earthquakes anywhere from a few decades to nearly a century long. And every time we have documented this, which is about four times now, it culminates with the granddaddy of them all: the big magnitude 8.8 to 9.0."

A region of the Sunda trench called the Mentawai fault is now getting restive. There was a big quake there last September. Meltzner and his colleagues suspect the September quake was the beginning of a quake cluster in a cycle that started in 1833 — one that is independent of the 2004 quake to the north. He thinks the cluster could culminate in a very large quake and perhaps a tsunami.

"It will probably happen in the lifetimes of children who are alive today," Meltzner says. He and his colleagues published their findings in this week's issue of the journal Science.

If a big one does hit again, Indonesia will be better prepared than it was in 2004. The government just inaugurated its own tsunami warning system, with help from several countries and the United Nations. Patricio Bernal, head of the U.N.'s Intergovernmental Oceanic Commission, says Indonesia now has numerous seismic and tsunami warning instruments in the Indian Ocean.

Bernal was in Indonesia recently when a medium-size quake hit. "They issued a warning overnight, and that warning did reach the population," he said. "So I am much more confident today that the system is slowly evolving to the point where they can be fully effective for warning the population."

The hard part, Bernal adds, will be staying vigilant over several decades.

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