Pete Gurr, a resident of American Samoa, was on his way to work when he felt an earthquake that originated 110 miles out at sea. Because of tsunami training he had received, he knew about the possibility of a deadly wave and drove down to the closest coastal village, where he warned the residents. Similarly, Tina Pule knew the earthquake was stronger than usual and told her parents to go inland.
Although they had just 10 to 15 minutes between the end of the shaking and the arrival of the first deadly wave to shore, many other American Samoa locals have similar stories of survival that USGS researchers heard when they arrived on the island to collect data immediately following the tsunami.
“Thanks to education efforts, thousands of locals had the knowledge to get to higher ground as soon as they felt shaking,” said Bruce Jaffe, a USGS oceanographer, who traveled to American Samoa with a rapid response team of tsunami scientists. “This research on water levels and sediment deposits immediately following a tsunami is an essential part of future education efforts because it is used to improve tsunami models — these are vital for designing evacuation routes, building stronger structures and determining the best areas for building.”
The USGS team also collected information to help interpret the geologic record to determine how frequently tsunamis of this magnitude are likely to strike American Samoa. Scientists can determine this frequency by examining sediment, because each tsunami that hits the area leaves a distinct, new sand layer or boulder deposit.
“We don’t know how often similarly large tsunamis strike American Samoa and whether larger tsunamis have hit the island in the past,” said Jaffe. “There are advantages to living on the coast, so people may live with the risk if it’s not likely that a tsunami this destructive will strike for a long period of time. This research helps us determine that risk.”
If the scientists had waited any longer than a week after the tsunami to collect this information, much of it would have been lost forever to clean-up efforts and natural processes. Just days after the tsunami, people were already scrubbing water marks from homes and removing debris, two of the best sources for determining where and how high the water flowed.
By continuing research on this tsunami, the USGS is working to improve the ability to interpret tsunami characteristics from the resulting deposits, determine the role coral reefs play in protecting the shore, and document and model how reef channels affect the tsunamis.
In addition to tsunami research, the USGS also sent a field party to deploy portable seismometers in American Samoa to detect aftershocks and collect valuable data for determining how ground motions vary in different parts of the island. This is a key parameter for making a seismic hazard assessment for American Samoa.
“Although we have come a long way in studying tsunamis in the last two decades, we must continue to focus on this kind of research because tsunamis are still poorly understood,” said USGS tsunami scientist Guy Gelfenbaum, who also traveled to American Samoa following the tsunami. “Having a better understanding of how a tsunami’s height and speed change as it moves onshore through this research will contribute to keeping people safe.”
Interviews with survivors, pictures of the damage, and maps of water heights used to make tsunami models can be found in “notes from the field” from this USGS team. The USGS team will continue to update this page as new information comes in.
USGS provides science for a changing world. For more information, visit www.usgs.gov.
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