The 28 March disaster caused devastation on the island of Nias. Credit: S. PLUNKETT/AP

Warnings about the risk of a tsunami after the recent earthquake in Indonesia spread faster and more widely than they did for last December's calamitous event, officials in the region say.

The latest earthquake struck off the coast of Sumatra on 28 March, just days before an interim tsunami warning system for the Indian Ocean was due to come into force on 1 April. But warnings were still delivered much more rapidly than they had been in December.

In the event, the magnitude-8.7 earthquake didn't generate a large tsunami. That was just as well, because when it struck, only a handful of the 25 countries in the interim warning system had provided names and numbers for national points of contact. “The earthquake happened before our deadline for receiving contact points,” says Keith Alverson, head of UNESCO's Global Ocean Observing System in Paris. (See Box 1)

Under the interim system, the US Pacific Tsunami Warning Center (PTWC) in Hawaii and the Japan Meteorological Agency will provide alerts on all seismic activity in the Indian Ocean region to round-the-clock contact points in the surrounding countries. The system, agreed in March (see Nature 434, 261; 2005 10.1038/434261b), is intended as a stopgap until 2006, when agreement is due on the details of a full-blown warning system based on tide gauges and seafloor pressure monitors.

The PTWC itself responded much more quickly and decisively than in December. Shortly after that quake it issued two bulletins — but only to members of the Pacific warning system. One, issued 15 minutes after the event, stated that a quake of magnitude 8.0 had occurred, with no risk of tsunamis to Pacific nations. The second, issued 45 minutes later, upgraded the quake to magnitude 8.5 and stated that there was “the possibility of a tsunami near the epicentre”.

The centre's team then also attempted to contact colleagues in Indonesia and Thailand, both members of the Pacific system. It was four-and-a-half hours before the PTWC sent a message to the Tsunami Bulletin Board — which goes by e-mail to international tsunami scientists and organizations — mentioning press reports of the disastrous tsunami.

The reaction was very different this time. Twenty minutes after the earthquake, the PTWC sent out a bulletin simultaneously to Pacific centres and to the bulletin board, warning that the event had “the potential to generate a widely destructive tsunami in the ocean or seas near the earthquake”. It explicitly advised evacuating coasts within 1,000 kilometres of the epicentre.

The PTWC also alerted the US Department of State, which sent messages to US embassies in the Indian Ocean region. The embassies, in turn, informed local emergency management agencies. “The PTWC now pays particular attention to the Indian Ocean; last time they weren't looking at it,” says Peter Pissierssens, head of ocean services at the Intergovermental Oceanographic Commission in Paris.

But international organizations report that responses to these warnings were patchy. The authorities in some coastal areas did issue prompt alerts and evacuated coastal areas. And vibrations from the earthquake itself were enough to send many people running inland. “There has been some progress in getting a warning system, but not a huge amount,” says Alverson.