A powerful 7.8-magnitude earthquake that hit the southwest coast of New Zealand on 15 July has given scientists a unique opportunity to show off their tsunami forecasting skills in real time.

New Zealand escaped the threat of a 'Great Wave'. Credit: Katsushika Hokusai (Japanese, 1760–1849)/ Metropolitan Museum of Art

Just as the quake struck at 21:22 local time, 90 leading tsunami researchers in Novosibirsk, Russia — six time zones west of New Zealand — were concluding a conference session.

Session chair Vasily Titov, chief scientist at the National Oceanic and Atmospheric Administration (NOAA) Center for Tsunami Research in Seattle, Washington, immediately grasped the threat — and the scientific opportunity. Less than half an hour after the quake happened, he demonstrated to the awe-struck audience a precise simulation of the tsunami that the quake would generate. "Absolutely amazing, that was the most spectacular real-time tsunami forecast ever," says Costas Synolakis, director of the University of Southern California's Tsunami Research Center in Los Angeles.

Titov, who helped to develop NOAA's web-based tsunami forecast system, fed data about the quake's location and magnitude into a model of regional tsunami effects.

Incorporating measurements being sent from a deep-ocean detection buoy off New Zealand, he predicted that the tsunami would not destroy the coastlines of New Zealand or Australia — before the first wave had even arrived at any large coastal communities.

Absolutely amazing, that was the most spectacular real-time tsunami forecast ever. Costas Synolakis , University of Southern California's Tsunami Research Center in Los Angeles

He was right. Tide gauges in New Zealand reported tsunami amplitudes of less than half a metre, with no flooding. The waves were still discernible from ordinary waves when they hit a beach, but small enough to cause nothing more than alarm. A tsunami warning issued by the Pacific Tsunami Warning Centre in Hawaii was in effect for about 2.5 hours after the quake hit.

Titov's live computation was the talk of the conference. At sessions this morning, he showed a more detailed analysis of yesterday's events. "It shows that we're getting there, that our methodology does work," says Synolakis.

Synolakis hopes that such accurate predictions can boost people's confidence in tsunami warnings. The Pacific system has been running for about 50 years, and a similar system is being created for the Indian Ocean, after a tsunami on 26 December 2004 flooded shallow coastlines and killed more than 220,000 people.

"We're all happy that New Zealand and Australia have got off lightly," says Viacheslav Gusiakov, head of the Tsunami Laboratory in the Institute of Computational Mathematics and Mathematical Geophysics in Novosibirsk, which hosted the 24th International Tsunami Symposium this week.

"What happened yesterday was also a perfect test case for what we're trying to do," he says. "I guess it has highlighted our ability to forecast tsunamis in real time, and to ultimately protect people from harm."