Warning and monitoring systems put in place following the 2004 Asian tsunami appeared to work well Wednesday after an 8.6-magnitude earthquake struck roughly the same area off Indonesia, according to officials, civic groups and citizens in affected areas.
The real test, however, will come with another disaster. Wednesday, no more than slightly higher than normal waves were seen in a few coastal towns along the southwestern coast of the Indonesian island of Sumatra, with no reports of deaths or major damage.
The rapid dissemination of warnings and evacuation of coastal areas throughout the Indian Ocean, including fairly isolated communities, were helped along by fresh memories of the earthquake-generated tsunami that battered the region in 2004, killing 230,000 people.
Also heading off complacency was the footage aired after Japan's massive March 2011 tidal wave and nuclear disaster, motivating people to take the risk seriously, even though ultimately the wave proved elusive.
"Things worked quite well," said Dailin Wang, oceanographer with the Pacific Tsunami Warning Center in Ewa Beach, Hawaii. The 2004 disaster "was not too long ago. People took it seriously and moved away from the coast. The challenge is to keep the knowledge alive."
Wednesday's earthquake, followed later by an 8.2-magnitude aftershock, was also deeper in the ocean and roughly twice as far from Sumatra as the 2004 temblor.
More importantly, it was of the strike-slip motion type often seen along the San Andreas Fault, said Bruce W. Presgrove, a geophysicist with the U.S. Geological Survey in Denver. That means tectonic plates move horizontally, which tends to displace less water and therefore presents less of a tsunami risk than quakes generating significant vertical movement.
Another factor that has helped in warning more people relative to 2004 is the prevalence of cellphones.
"The mass media, mobile telephones and [short messaging] mainly contributed to getting the word out," said Suresh Bartlett, the World Vision charity's director for Sri Lanka.
Sirens sounded along coastlines, and warnings spread like wildfire by mobile phone text messaging. Though often chaotic, evacuations began immediately, with streets clogged with traffic, especially in Indonesia's Aceh province, where 170,000 people were killed in 2004.
Countries all along the Indian Ocean -- from Australia and India to as far off as Africa -- received alerts from the Pacific Tsunami Warning Center, saying they should prepare for the possibility of seismically charged waves.
The tremors were felt in neighboring Malaysia, where high-rise buildings shook, and Thailand, India, Singapore and Bangladesh.
The Associated Press contributed to this report.