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Tsunami Forecast Model Animation: Chile 2010

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At 3:34 on the morning of February 27, 2010 (06:34 UTC), an 8.8 moment magnitude earthquake struck near the coastline of central Chile. The Pacific Tsunami Warning Center (PTWC) quickly determined that the large magnitude of this earthquake, its location near the coastline, its relatively shallow depth within the earth, and a history of megathrust earthquakes in the region meant that it could have moved the seafloor and thus posed a significant tsunami risk and PTWC issued their first tsunami warning several minutes later for Chile and Peru. The earthquake did in fact cause a tsunami, and over the following hours as PTWC learned more about the earthquake (confirming it was a megathrust and upgrading its magnitude) and its tsunami through forecast models and direct observation with DART sensors and coastal sea-level gauges PTWC would eventually issue tsunami warnings to the State of Hawaii and all 43 countries and territories participating the Pacific Tsunami Warning System, keeping warnings in some areas in effect for more than a day. PTWC’s sister office, the West Coast and Alaska Tsunami Warning Center (now known as the National Tsunami Warning Center), also issued tsunami advisories for Alaska and the Pacific coasts of the United States and Canada. The tsunami caused the greatest devastation and 124 deaths in Chile, where waves reached as high as 29 m or 95 ft. on the mainland, over 18 m or 60 ft. in its Juan Fernandez Islands, and over 4 m or 14 ft. at Rapa Nui (Easter Island). Outside of Chile tsunami wave heights exceeded 1 m or 3 ft. in the Marquesas Islands (French Polynesia), New Zealand, the Kuril Islands (Russia), and in the United States in California and Hawaii, and caused minor damage in San Diego, California and in Japan.

The Pacific Tsunami Warning Center (PTWC) can create an animation of a historical tsunami like this one using the same tool that it uses to determine tsunami hazards in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they travel through the world’s oceans one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).

Toward the end of this simulated 30 hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” are hit by larger waves than those to either side of it.

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Earthquake source used: USGS NEIC W-Phase CMT

http://earthquake.usgs.gov/ear....thquakes/eqinthenews

For a NOAA Science on a Sphere version of this animation, please see:

http://sos.noaa.gov/Datasets/dataset.php?id=597

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