April 11, 2012 -- A massive 8.6 magnitude earthquake struck off the coast of Indonesia early today, triggering an Indian Ocean tsunami that alarmed people throughout the region, but caused little damage.
The quake was centered 20 miles beneath the ocean floor about 270 miles from Aceh's provincial capital.
The tremor was felt in Singapore, Thailand, Bangladesh, India and Malaysia, where tall office buildings shook for more than a minute, according to the Associated Press.
An 8.2-magnitude aftershock was reported off the coast of northern Sumatra with an epicenter 382 miles from Banda Aceh, Sumatra, Indonesia, around 6:43 a.m., according to the U.S. Geological Survey.
"A significant tsunami was generated by this earthquake," the National Oceanic and Atmospheric Administration's Pacific Tsunami Warning Center said today. At its highest, waves tsunami waves rose 3.5 feet.
The tsunami alert was terrifying for people who still have fresh memories of the 2004 tsunami that devastated Indonesia's islands.
Workers at the Hermes Palace Hotel in Banda Aceh described a scene of panic, near the coast, as people fled to higher ground. Employee Cut Arlista said the shaking was so strong that water from the hotel pool spilled out, although the 70 guests at the hotel were not evacuated.
"People were crying, and everybody was running inland as fast as they can," Arlista told ABC News.
But there was little damage reported by the wave and the tsunami warnings were lifted a short time later.
The nature of the quake made it less likely a tsunami was generated because the earth moved horizontally, rather than vertically, and therefore had not displaced large volumes of water, Bruce Presgrave of the USGS told the BBC.
"We can't rule out the possibility, but horizontal motion is less likely to produce a destructive tsunami," he said.
Still, the Pacific Tsunami Warning Center in Hawaii said a tsunami watch was in effect for Indonesia, India, Sri Lanka, Australia, Myanmar, Thailand, the Maldives and other Indian Ocean islands, Malaysia, Pakistan, Somalia, Oman, Iran, Bangladesh, Kenya, South Africa and Singapore, according to the AP.
The tsunami warning was extended until 9 a.m. E.T.
The latest quake struck off the west coast of Sumatra, the same region devastated by a magnitude-9.1 earthquake in December 2004. That tremor triggered a catastrophic tsunami in the Indian Ocean that killed 230,000 people.
"I think a lot of people learned from the past," Arlista said. "Everybody knew to run as soon as the earthquake hit."
Gary Peart, an Australian worker at the Lumba Lumba Diving Center on the beach in Banda Aceh in the province of Aceh, Indonesia, said the quake lasted quite a while.
"It was long for an earthquake," he said. "Maybe a minute and a half, and then it got slowly, slowly stronger, and then it faded away."