The most dangerous thing that can happen in the eerie vacuum between an earthquake and a tsunami is nothing. Once a tsunami warning is issued, the size of the wave and the number of minutes before it arrives comes into focus slowly, as scientists at alert centers around the world piece together information about the quake’s location and impact. But people living on the water’s edge need to move fast. Once residents feel a big quake, they aren’t likely to wait around to find out when and if the wave will follow — especially if it has happened before.
On Wednesday afternoon, an 8.6 earthquake struck some 300 miles off the northern coast of the Indonesian island of Sumatra, a region that was devastated in the 2004 Boxing Day tsunami. The U.S. government’s Pacific Tsunami Warning Center in Hawaii immediately issued alerts from South Africa to Singapore, a wide swath unnervingly similar to the areas hit eight years ago. Scenes of panic unfolded across South and Southeast Asia as the quake and ensuing alerts sent residents scrambling for higher ground, clogging up roads.
By evening, there were no reports of casualties, major damage or large waves, but alerts remained in place. The Indonesian government reported that three waves of up to 2.5 feet had hit their coastline, and officials in India’s Andaman and Nicobar islands were expecting surges of up to 12 feet. “It doesn’t look like a major tsunami,” an official on duty at the Pacific Tsunami Warning Center told Reuters. “But we are still monitoring as tsunamis come in waves.” By nightfall, the AP reported that most of the tsunami watches had been lifted.
It’s terrible to think about so many people forced to relive any part of what they witnessed in 2004, when over 230,000 people were killed in more than a dozen countries. But the fact that so many people today were immediately mobilized is nevertheless an encouraging mark of progress in the region’s emergency preparedness. Within an hour of the first quake (several aftershocks followed), Indonesia’s National Agency for Disaster Management had issued a tsunami alert and dispatched a disaster management team to Banda Aceh, the coastal city hit hardest in 2004. About two hours later, after a large aftershock, the nation’s geophysics agency had extended the local tsunami alert by two hours.
People are reporting similar levels of organization in other areas under alert. On the west coast of Phuket, the Thai resort island that was devastated in the 2004 tsunami, people were evacuated quickly after the quake. “People were running out of shops along our road and heading towards higher ground,” said Chaiyot Yongcharoenchai, chief reporter for the Phuket Gazette. “Traffic is totally jammed with people trying to get away from the beaches.” But at least one official from the government’s Disaster Prevention and Mitigation Center was immediately on the ground, answering people’s questions and keeping an eye on the water to make sure it wasn’t receding. Despite there being no signs of that happening, the Center ordered people to remain evacuated for several more hours.
When the Boxing Day tsunami struck in December 2004, this kind of preparedness was simply not there. The wave struck some of the poorest regions in Asia, where early warning systems were not in place. Where they were, word was often too slow to reach residents and tourists in time to warn them what was coming. Survivors recounted watching neighbors wade onto the wet, empty beach as the tide dramatically receded with the pull of the coming wave. It may seem hard to imagine today, but before 2004, most of the world was blissfully ignorant of what a tsunami looked like. Since then, deadly tsunamis have wiped away whole towns in Chile in 2010 and Japan in 2011. Nations where people were killed in 2004 have since ramped up or established their own early warning systems— Indonesia, for example, beefed up its pre- and post-emergency response legislation in 2007, and India established an early warning system the same year.
Social media is another big part of what’s changed. Twitter in particular has come to play a crucial role in spreading information about natural disasters as they unfold. Within less than an hour after the quake today, seven of the top ten worldwide trending terms on Twitter were #PrayForSumatera (sic), #tsunami, Indonesia’s President, Indian Ocean, Sumatra, Magnitude 8.7 and Pacific Tsunami Warning Center. People are getting alerts on their smartphones and spreading that information immediately, as seen in one early tweet from a woman who was in Phuket: “Felt #quake~ 30 sec. before my iPhone sent me SMS. Now sitting with 100′s on a hill. No news of #tsunami.” In Japan, too, it’s common now for people to have an earthquake alert app on their phones that chart the thousands of aftershocks that have been taken place since the 9.0 quake struck off northeast Japan last March 11.
Of course, even when the word gets out, there is only so much that can happen in the brief window nature offers. Japan, a seismically active archipelago, has been living with the specter of tsunamis for as long as it has been inhabited. When the earthquake hit last year, the world’s most advanced early warning system kicked into gear and tsunami warnings were issued within three minutes. Local officials got on speaker systems that are installed throughout towns on the coast and started ordering people to evacuate. Residents knew exactly what that quake meant — run — and still as many as 20,000 people died, swept away in their cars or before they could get out the door. Today, communities around the Indian Ocean rim seem to have been spared a tragedy of that magnitude. It’s a huge relief, and so is the fact that when and if a big wave does come, nothing won’t happen again.
With reporting by Robert Horn/ Bangkok and Amantha Perera/ Colombo
Mahr is a correspondent at TIME. Find her on Twitter at @kristamahr.