PTWC releases video of past Chilean earthquakes to explain tsunami waves

Photo credit NOAA/NGDC, Herb Hardin.
Photo credit NOAA/NGDC, Herb Hardin.

The Pacific Tsunami Warning Center released a video on YouTube to show a side-by-side comparison of three tsunamis generated from Chile earthquakes.

The video highlights two important characteristics of tsunami behavior:

  • The height of the tsunami waves (as shown by color) is strongly dependent on the size of the earthquake, namely its moment magnitude (Mw). The 9.5 Mw earthquake of 1960 released approximately 11 times more energy than the 8.8 Mw earthquake of 2010 and approximately 89 times more energy than the 8.2 Mw earthquake of 2014. Likewise, the tsunami wave heights were far larger in 1960 than they were in 2010, and larger in 2010 than they were in 2014.
  • The speed of a tsunami does not depend on the size of the earthquake. All three tsunamis move at about the same speed regardless of their size because their waves are so large that they interact with the sea floor. Therefore, both the ocean depth and its local variations control the speed of the tsunami waves.

These two characteristics are taken into account when the PTWC issues tsunami warnings.

PTWC analyzes earthquakes and their estimated magnitudes to determine the level of a tsunami warnings, if any.

Knowing tsunami waves move at a speed about 50 times slower than earthquake waves, the PTWC can issue warnings well in advance of a tsunami’s arrival except for those nearest to the tsunami-causing earthquake.

According to the PTWC, the 9.5 Mw earthquake in May 1960 that struck Chile is the largest earthquake ever recorded. The number of fatalities associated with both the earthquake and tsunami has been estimated to be between 490 and 5,700. The Chilean government estimated 2,000,000 people were left homeless and 58,622 houses were completely destroyed.

The tsunami reached across the Pacific and devastated Hilo, killing 61 people.

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