Why the Alaska Earthquake Didn't Produce a Large Tsunami


Early Tuesday morning, a large 7.9M earthquake occurred off the coast of Alaska, triggering Tsunami Alerts for much of the US West Coast and Alaska. Even thought Tsunami Watches and Warnings were issued, no major tsunami occurred. This isn't unusual, as the watches and warnings are often issued to give residents a heads up that something may occur. Think of it like tornado warnings. You may not get a tornado every time, but you should still take action to protect your life!

A small, local tsunami was observed near the epicenter along the Alaska coast, but the waves didn't travel far. The reason likely was the type of earthquake that occured. Today's earthquake was a result of strike-slip fault movement. In this type of earthquake, the faults move horizontally. This doesn't displace too much water. In other types of earthquakes, such as a thrust or reverse earthquake, where the ground moves up, more water is displaced. This would have resulted in a much larger tsunami.

One more interesting thing to note is that local seismographs, devices used to measure the energy waves associated with earthquakes picked up this morning's large quake. Note the blue lines on the Virginia Tech Seismograph. That's the energy waves moving through the earth's crust beneath us. Of course, we don't feel anything, because the waves are much weaker, but they still register on seismographs around the world in a large earthquake like this. Pretty cool!

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