By Gregg Kleiner and Kirk Richardson
When the Cascadia subduction zone earthquake strikes 50 miles off North America's west coast, people from northern California to Canada will have only 15 to 30 minutes to move to higher ground before the ensuing tsunami inundates coastal areas.
"When it comes to tsunamis, minutes matter," said Dan Cox, a professor of civil engineering. Cox is part of an Oregon State cross-disciplinary research team that is developing a computer tool to model various evacuation scenarios. His collaborators on the project are Haizhong Wang, an assistant professor in civil engineering, and Lori Cramer, an associate professor in sociology. Their research is funded by Oregon Sea Grant.
Tsunami evacuation scenarios can be challenging to analyze, because they involve human behavior, split-second decision-making, multiple modes of transportation and the fluid mechanics behind a massive wall of water. The researchers hope that the tool will help beach visitors, city officials, State Park staffers and other coastal residents plan for the tsunami scientists say the Really Big One will unleash.
When Cox launches the tsunami simulation tool on his computer, colored dots — representing people on the beach — start moving on the screen in real time. These virtual people follow several evacuation routes that lead away from the beach toward safe zones on higher ground. Soon, a blue wave appears onscreen, washes onto land and inundates beaches and other low-lying areas.
When the animation ends, Cox points to some of the dots that are now covered in blue.
"Some of the people here, who chose to go along the jetty route, didn't make it," he said. "And in this area, people who walked along this route would have made it to safety. Those who went back to their cars didn't escape because of the bottleneck."
Cox was initially quite surprised at this result.
"We can vary the walking speeds, driving conditions and all of those kinds of inputs, but it still plays out that there are huge differences in survivability based on people's choices," he said. "And that's the value of these models."
The team is trying to illustrate that making what might appear to be minor changes to an evacuation plan can make major differences in terms of survivability. Sometimes the shortest route is not necessarily the safest. And although many people fleeing a tsunami will turn to vehicles for evacuation, Wang said that using a car or truck is not a fail-safe solution, because damage to roads and bridges caused by the earthquake that precedes a tsunami can cause traffic problems and create chaos. "While you might be able to get to your vehicle and start driving, you don't know what you'll encounter in road infrastructure and traffic conditions ahead of you,” he said. “For example, if a bridge is destroyed, people have to find other ways to cross a river or inlet, and vehicles abandoned in traffic jams or at accident scenes can cause dangerous bottlenecks.”
Wang, an expert in post-disaster transportation network resiliency, has done research to try to understand how evacuee decision-making behavior impacts traffic flow. He takes various transportation modes, such as automobiles, pedestrians and bicycles, into account.
“A tsunami evacuation is likely to be multi-modal,” said Wang. “This tool lets us view different kinds of scenarios. For instance, we can evaluate different pedestrian and vehicle speeds to see how cars and pedestrians interact in an emergency scenario, and how that impacts the mortality rate.”
Cramer brings her expertise in social behavior to the project. She is contributing valuable information on individual and group behavior and decision-making during emergencies.
“We’re trying to understand the parameters that go into the models,” she said. “What are the decisions that people make before they decide to leave?”
For example, the amount of time people spend between first feeling the earthquake and taking action is called milling time. The researchers can adjust milling time in their model to show people that taking quick, decisive action can increase the odds of survival. The next step of the research project will be talking with people living in or near tsunami inundation zones to better understand how they might think and react in the wake of a tsunami alert.
“We can’t predict what every person is going to do, but we can help inform and educate so they can be better prepared for the event before, during and after, in order to maximize lives saved,” said Cramer.
To further inform the research, it is important to understand the unique challenges of various populations who work and live in tsunami inundation zones.
“This tool is a great start, but until we’re able to have others tell us how we can best use it, we’re not there yet,” she said. “We have to recognize that there is a lot of diversity within a community in terms of social vulnerability and that these scenario models can inform some of that planning. We need to make sure that we communicate with community members, bring those voices into this process and not assume that a one-size-fits-all model is going to work.”
Researching a complex topic like tsunami evacuation methods from multiple angles and disciplines might not lead to a comprehensive solution, but it has the potential to make a significant contribution to education and planning in coastal communities. And ultimately, it will save lives.