This post has been corrected. See note at the bottom for details.
NEW DELHI -- Warning and monitoring systems put in place after the 2004 Asian tsunami appeared to work well Wednesday after an 8.6-magnitude earthquake that struck roughly the same area off Indonesia, said officials, civic groups and citizens in affected areas.
However, the real test will only come with another major disaster.
Fortunately, no more than slightly higher than normal waves were seen in only a few coastal towns along the southwestern coast of Sumatra island, with no reports of deaths or major damage.
The rapid dissemination of warnings and relatively rapid evacuation of coastal areas throughout the Indian Ocean, including fairly isolated communities, were helped by fresh memories of the tsunami that battered the region eight years ago, killing 230,000 people.
Also helpful was the footage aired after Japan’s massive March 2011 tsunami and nuclear disaster, motivating people to take the risk seriously, even though ultimately the wave proved elusive. From a public safety perspective, complacency is often the biggest killer, especially if people have not experienced or heard about a tsunami in decades.
“Things worked quite well,” said Dailin Wang, oceanographer with the Pacific Tsunami Warning Center in Ewa Beach, Hawaii. The Indonesian earthquake and tsunami of 2004 “was not too long ago. People took it seriously and moved away from the coast. The challenge is to keep the knowledge alive.”
The earthquake was also deeper in the ocean and roughly twice as far from the Indonesian island of Sumatra as the 2004 temblor that generated that year’s tsunami.
More importantly, it was of the strike-slip motion type often seen along the San Andreas Fault, said Bruce W. Presgrave, a geophysicist with the U.S. Geological Survey in Denver. That means tectonic plates move horizontally, which tend to displace less water and therefore present less of a tsunami risk than quakes generating significant vertical movement.
“In general, for an earthquake of this size, it’s prudent to issue things like this warning, even if a tsunami didn’t occur,” he said. “Prudence saves lives.”
According to the U.S. Geological Survey, the powerful quake was centered 20 miles beneath the ocean floor around 308 miles from the provincial capital Aceh on the Indonesian island of Sumatra.
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 director for Sri Lanka based in Colombo. “The news got to everybody. Of course the roads were a bit congested as people tried to get to higher ground.”
So long as transmission towers and telecommunication infrastructure remain in place during a disaster, mobile phones can be more effective than tsunami sirens, which end up being posted every few miles and sometimes out of earshot, Wang said.
Television footage immediately after Wednesday’s earthquake showed terrified Indonesians pouring into the street, making cellphone calls and hugging each other in fear, some going back into buildings to find lost colleagues.
Indonesian officials said lessons learned from 2004 were applied.
"The early warning system in [the affected areas of] Aceh and Padang and the west coast of Sumatra is much better,” said Sutopo Nugroho, data information chief at the National Disaster Mitigation Agency. “People have fled to mosques and churches in the affected areas. We have established better communication networks and we know from speaking with them that a tsunami has not struck."
On the timeline front, the oceanographer Wang said Hawaii’s Tsunami Center sent an alert to the U.S. Geological Survey within six minutes of Wednesday’s earthquake, which hit at around 2:30 p.m. local time in Indonesia (12:30 a.m. PDT). It issued a tsunami watch approximately a minute later to countries across the Indian Ocean region, he added, that included a warning that 28 nations were potentially vulnerable.
Officials in Sri Lanka, Thailand, Indonesia, India and Pakistan reported that their system all worked well.
As warnings were rescinded worldwide, experts breathed a sigh of relief.
“Fortunately nothing too bad happened,” Wang said, “this time.”
[For the Record, 2:22 p.m. PDT April 11: An earlier version of this post incorrectly spelled geophysicist Bruce W. Presgrave’s last name as Presgrove. It also incorrectly referred to the 2011 tsunami in Japan as a tidal wave. Additionally, the magnitude of the quake, earlier estimated as 8.7, has been lowered to 8.6.]
-- Mark Magnier
Special correspondent Kate Lamb in Jakarta, Indonesia contributed to this report.
Photo: People look at walls damaged by a strong earthquake at a prison in Aceh province in Indonesia on Wednesday. Credit: Associated Press / Kyodo News.