TsunamisThe Accuracy of Tsunami Predictions
Residents of coastal towns in Chile remember the catastrophic earthquakes that struck their country in 1960 and 2010, not always for the quakes themselves but for the tsunamis that followed. New study validates accuracy in predicting the first wave, but weakness in forecasting ‘trailing’ waves.
Residents of coastal towns in Chile remember the catastrophic earthquakes that struck their country in 1960 and 2010, not always for the quakes themselves but for the tsunamis that followed.
Those who survived the 9.5-magnitude 1960 quake told interviewers about the man in Maullin, Chile who, after the first wave of the tsunami, rushed into his dockside warehouse to retrieve possessions just as the second wave hit. The second wave swept the warehouse out to sea and the man was never seen again. Similarly, waves following the first one, known as trailing waves, made post-tsunami rescue efforts in 2010 life-threatening.
In 2010 society had better tsunami-warning technology than in 1960, but weaknesses still existed. New research by geophysicists at Scripps Institution of Oceanography at UC San Diegoreveals the strengths and shortcomings of tsunami early warning systems as experienced in the 2010 episode. The study is representative of much of scientific research in that it does not create new prediction tools but contributes to assessing the reliability of existing methods. The scientists hope the work can improve predictions of trailing tsunami waves.
Ignacio Sepulveda Oyarzun, a postdoctoral fellow at Scripps Oceanography who himself survived the 2010 Chile earthquake, and colleagues found a weakness based on inaccurate estimates of bathymetry, which is the topography or depth of the seafloor. That inaccuracy doesn’t matter so much when an initial, or leading, tsunami wave hits because of its sheer size, but trailing waves have short enough wavelengths that they are considerably more influenced by the shape of the seafloor over which they travel on their way to coastlines. Trailing wave forecasts are severely affected by bathymetry errors, said study authors, with wave amplitude uncertainties off by as much as 35 percent.
Sepulveda said there is good news in this work in that it validates the accuracy of leading tsunami wave warnings but also provides the caveat that people need to stay away from coastal areas for several hours after the initial wave because of the unpredictability of what happens next.
“We have wondered about the impact of bathymetry errors on tsunami models for a long time because bathymetry data is a critical input of the models,” said Sepulveda. “With this new study, we are now able to answer valuable questions about the reliability of tsunami warnings and hazard assessments.”
