Unlike 2004 disaster, faults in crust moved from side to side, instead of up and down
The magnitude-8.6 earthquake that struck in the Indian Ocean off
the western coast of Sumatra today resurrected fears of a repeat of the
2004 Indian Ocean earthquake and tsunami that proved one of the most
devastating natural disasters in modern memory.
What causes earthquakes?
What causes earthquakes?
However, this earthquake, which struck at 2:38 p.m. local time (4:38
a.m. ET), about 270 miles (435 kilometers) off the coast of the
Indonesian island, was a different animal altogether than the 2004 earthquake and tsunami, which killed more than 230,000 people and left millions homeless.
"It was quite a bit smaller," said Julie Dutton, a geophysicist with
the U.S. Geological Survey. The 2004 quake was a magnitude-9.1 — the
third most powerful earthquake ever recorded.
Perhaps more significantly, today's earthquake was a different kind
of quake all together. Instead of occurring at a plate boundary along an area called a subduction zone,
where one tectonic plate is diving beneath another, this earthquake
occurred in the middle of an oceanic plate, where the faults in the
crust essentially moved from side to side instead of up and down. These
sorts of events are called strike-slip earthquakes.
"With a strike-slip event you don't have the same potential hazard
for a tsunami as you do with a subduction event because the plates are
moving adjacent to each other," Dutton told OurAmazingPlanet.
GRAPHIC: How tsunamis occur
Although they are sometimes produced by landslides on the seafloor,
significant tsunamis are typically created by subduction earthquakes,
when one massive oceanic plate suddenly lurches deeper beneath another
plate, shoving up a huge section of the seafloor. That displacement of
the ocean floor also displaces ocean water. Essentially, the more ocean
floor you move, and the more dramatically you move it, the more water
you move, and the bigger the tsunami you get.
Just minutes after the earthquake struck today, the U.S. Pacific
Tsunami Warning Center in Hawaii issued a tsunami watch for the entire
Indian Ocean region.
A little more than an hour after the first and largest quake hit, the
watch was still in effect, and tsunami wave heights of 1 foot were
recorded in Sabang, in Indonesia's Banda Aceh province, the region that
was most affected by the 2004 disaster.
The largest tsunami produced was about 3 feet (1 meter) high, according to the tsunami warning center, which has now canceled all watches for the area.
Dutton said that it is unusual to see such a powerful earthquake in
the region where today's quake struck, "but it's not unheard of," she
added.
Reach Andrea Mustain at amustain@techmedianetwork.com. Follow her on Twitter @AndreaMustain.
Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.
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