By Memorie Yasuda

How Do We Know if a Tsunami Is Approaching?

Tsunamis do not occur after every large earthquake. If they did, there would be tsunami warnings regularly, because sizeable earthquakes happen almost daily somewhere on Earth. Generally, only earthquakes that rupture the oceanic crust generate tsunamis, and only those that produce significant vertical displacements generate large tsunami waves.

So all earthquakes do not generate tsunamis, and people generally do not want to evacuate unless they are certain that a tsunami is coming.

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Today, sophisticated sensors detectors check continually for tsunamis, particularly after a major undersea earthquake. Instruments located on the seafloor all around the ocean detect changes in the pressure of seawater as a result of passing tsunami waves. The instruments are connected to buoys at the surface that relay information to satellites.

When a tsunami is detected, a warning is sent through an emergency network. The network must then pass this information along to people who are in danger, something that took too long during the recent tsunami. As a result, better warning systems are being planned and built in the Indian Ocean region today.

For areas around the Pacific Ocean, two centers provide warnings: the Pacific Tsunami Warning Center, established in Hawaii after 159 people died in a tsunami that took Hawaii by surprise in 1946, and the West Coast/Alaska Tsunami Warning Center in Alaska that serves coastal areas around the continental United States including California.

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