On Dec. 26, 2004, one of the largest recorded earthquakes struck off the Indonesian island of Sumatra, heaving a piece of seafloor roughly the length of California about 36 feet sideways and 16 feet up. Some 6,000 aftershocks followed.
The tsunami that rose from this great shifting of tectonic plates reached over 115 feet in some places and ultimately killed about 230,000 people in Indonesia, Thailand, Sri Lanka, India, the Maldives and East Africa. If there had been a natural hazards misery index, it would have registered off the scale.
About one in 28,000 people on Earth perished that day because governments were ill equipped to warn residents and visitors about the coming wave and guide them to safe evacuation routes. India failed to warn people on its eastern coast even after the tsunami wreaked havoc in the Andaman Islands, hours before striking the mainland. In Phuket, Thailand, tourists who were mesmerized by the sudden withdrawal of water roamed the exposed seafloor and then were caught unaware by the rushing water. In the Maldives, men asked women and children to stay indoors, where they could not escape the flooding. The men climbed trees and onto roofs when they heard the roar, leading to a lopsided death toll.
Today people around the world are far likelier to receive a timely warning to evacuate a giant, dangerous wave. But as a Dec. 5 earthquake and (tiny) tsunami off Northern California showed, we can’t rely on just seismic information to generate warnings. That recent tsunami was only about two inches high by the time it reached the coast, but millions of people received a warning, triggering some to evacuate unnecessarily. A lot of the confusion would have been avoided if there had been more specific information for different locales, and this is entirely possible to provide.
In the 20 years since the Indian Ocean calamity, the Pacific Tsunami Warning Center started providing warning services to Indian Ocean countries. Scientists identified other high-risk zones around the world and modeled potential tsunamis. The National Oceanic and Atmospheric Administration, in conjunction with the United Nations, began training Indian Ocean scientists, emergency managers and sometimes even politicians in how to perform hazard assessment studies, do public outreach and produce inundation maps for evacuation planning and signage. The objective was to eventually provide targeted warnings and then update such warnings as new data comes in.
Before 2004, the Pacific had the only six tsunamographs in the world — buoys anchored to the deep ocean that detect tsunamis and transmit the information to satellites, which in turn transmit to tsunami warning centers. Now there are about 60 in the Pacific and the Caribbean and about 10 in the Indian Ocean. There are none in the Mediterranean.
In Northern California this month, a tsunami warning was issued for a coastal zone stretching about 600 miles along the Pacific Ocean within five minutes of the earthquake. Local authorities also activated the Wireless Emergency Alert system, and an estimated five million people from the San Francisco Bay Area to the central Oregon coast got phone alerts advising them of the tsunami threat. Unlike during the wildfires that burned the town of Paradise, Calif., in 2018 and the town of Lahaina on Maui, Hawaii, in 2023, people received the message whether they had social media accounts or not.
The problem was that the warning did not provide flood depth estimates or information on how quickly the water levels were expected to rise and then fall in different locales along the coast. The warning centers and California did not have the technology to do so and had no choice but to err on the side of caution.
With better technology, we could further shorten the time between the event and when the warning goes out — and make warnings more specific to various sites, instead of blanketing a large area.
More tsunamographs and seafloor seismometers are essential, and machine learning could provide worst-case estimates of inundation, moments after shaking ends, leading to targeted warnings and effective evacuations of at-risk areas. People need to know how much time they have to evacuate, where to go and how to refer to signage to get them there.
Worldwide, tsunami preparedness still varies, too. A real outlier is the Mediterranean, where there is substantial risk of up to two large events per century. In the Aegean Sea, where there are over 200 inhabited islands and tens of millions of tourists every year, only about 10 tidal gauges are transmitting data.
Tens of millions of euros have been spent in the Mediterranean to try to calculate tsunami probabilities, but only a small fraction of that has been spent to improve onshore preparedness. In the United States and its territories, there are 200 tsunami-ready locales, a designation that asks communities to have evacuation maps, signage and sustained public education efforts. But there are only five in the Mediterranean. The only silver lining is that Wireless Emergency Alerts are rapidly becoming common in Southern European countries — sadly, though, not in North Africa.
Site-specific warnings are technologically feasible everywhere. And there is no excuse for not having evacuation maps and signage for tsunamis. National and international organizations such as the National Atmospheric and Oceanic Administration, the Joint Research Center of the European Commission and the World Meteorological Organization need to work together to develop a warning system that has been rigorously tested, to protect residents and visitors.
Until then, if you are near a beach and feel a tremor that lasts over 15 seconds or you observe unusual shoreline motions that resemble a fast-rising or fast-receding tide, you should not wait for an official warning. You should follow tsunami evacuation signs or move immediately to an elevation of at least 50 feet above the waterline and wait there until an all-clear. That way people, no matter where they are, can avoid the fate of the 230,000 in 2004.
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