I'm thinking we can handle the next tsunami that comes to us from far away. It could be bigger than what hit on March 11, 2011, and there's a good chance it won't strike at low tide. But if we have five or more hours of warning, and continue to hold drills, test the systems, and educate people to stay out of the tsunami zone, we should do OK. I'm worried about the earthquake that happens right here and the tsunami surges that arrive as little as 10 minutes later.
On Jan. 26, 1700, the Wiyot, Yurok, Tolowa and other native peoples of the coastal Pacific Northwest were at ground zero when the last great Cascadia earthquake occurred. Their oral history describes the strong ground shaking, the changes in land level and the ensuing tsunami that arrived soon after. Our 1700 tsunami was large enough to travel across the Pacific and cause damage in Japan. From the Japanese accounts, we can work backwards to determine the date and estimate just how large the Cascadia earthquake source had to be. Most scientists concur that it was about a magnitude 9.
I have spent much of my research career studying how people survive tsunamis, particularly in areas close to the earthquake source. I have visited coastal areas of six countries after they were devastated by a “near-source” tsunami, including three trips to Japan since March 11, 2011. I have seen concrete buildings toppled over like dominos, ships perched on land hundreds of feet from the coast, and once-thriving
The lesson I have learned and relearned with every trip: People survive when they take immediate action and evacuate, people die when they don't. This isn't as simple as it seems. How people perceive risk, process risk factors and decide to take action depends on what they know, what they perceive and how they process the information. Our first response to a situation we have never experienced before is often denial that anything is wrong. Japanese social scientists call this “normalcy bias.” In Japan, most people took almost 20 minutes before they began to evacuate after the earthquake. And these were the folks who survived.
The purpose of sirens and media announcements and officials knocking on your door is to get your attention, knock you out of the denial phase and convince you to take action. The more of these triggers you experience, the more likely you are to respond. Unfortunately, when the earthquake is nearby, none of the components of the official warning system is likely to work.
In 2005 I visited the Aceh coast of Northern Sumatra, the area hit hardest by the 2004 Indian Ocean tsunami. In community after community, the buildings were erased, and most people died. The survivors had never heard about tsunamis beforehand.
Our last stop was Simeulue Island. We visited Langi Village, the community closest to the earthquake epicenter, where the tsunami arrived only eight minutes after the earthquake. Surges reached 30 to 40 feet and leveled every structure in the village. I expected the same desolation to greet me in Langi that I had seen in Aceh. I was wrong. In Langi, not a single man, woman, or child died in the tsunami. Langi had the shortest amount of time before the tsunami arrived, and yet every person survived.
What was different about Langi? The village had no electricity, no computers, and no technological warning system. They had a cultural warning system instead. Tsunami stories were passed from one generation to the next. If the ground shakes for a minute or longer, everyone knows what to do. Adults grab the children, put the elderly in carts and head up the hill to where supplies are stored. And they stay there -- for days. They know from experience that the danger period can last a long time.
Strong earthquakes are common in Sumatra, but great tsunamis are rare. The last deadly tsunami hit Langi in 1907. There have been dozens of strong earthquakes since then. For them, every earthquake is an opportunity to practice their evacuation skills whether it produces a tsunami or not. On Dec. 26, 2004, they got it perfectly right.
Lori Dengler is professor and chair of the Geology Department at Humboldt State University and an expert on tsunami education and mitigation.