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5 things Californians should know about tsunamis




Tsunami Hazard Zone sign on California coast.
Tsunami Hazard Zone sign on California coast.
Cal OES/Flickr Creative Commons

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Early Thursday morning, a magnitude 6.5 earthquake shook parts of Northern California, although the quake itself occurred 100 miles off the coast of Eureka. While tremors were felt on land, no damage or injuries have been reported, and there appears to be no danger of a tsunami.

This quake has some wondering, what would it take for a tsunami to hit the California Coast?

Take Two's A Martinez spoke with Elizabeth Cochran. She's a seismologist with the U.S. Geological Survey. 

1. Risk for tsunami really depends on the quake's location

If we had a subduction zone event— that's where you would have the sea floor being pushed upwards and as a result the water would also be pushed upwards and then flow away from that spot— that's when you get a tsunami generated.  

Going up further north in California and into Oregon and Washington, there's a pretty high hazard for tsunamis if there's a large earthquake. 

2. Long distance quakes have been felt in California 

This area is a fairly active area for earthquakes, even as large as the one we saw today. The nice things about this earthquake— if there is something nice about earthquakes— is that it occurred about 150 kilometers offshore. And so, there was only moderate shaking that was felt onshore. 

We could have a tsunami affect the entire west coast of the U.S. from a large magnitude earthquake that occurs as far away as Alaska or even in Japan. So you can have these tsunamis that travel across the entire ocean basin and affect regions fairly far away.  We have seen that in the past with some larger events. 

3. The risk is different in Northern and Southern California

The very northern most part of California where this event occurred is at the highest risk for a local tsunami. And that's because they have the offshore faults that are capable of generating tsunamis. Down in Southern California, we have a few offshore faults but they pose lower hazards to generation of tsunamis. 

4. The time from quake to tsunami wave could be minutes or hours

It depends how far away you are from where that earthquake occurs and where that tsunami is generated. Tsunamis travel approximately at the speed of a jumbo jet so it can actually take hours for a tsunami to transverse across the Pacific Ocean. 

For those types of events where you're looking at tsunamis generated far away, there are a number of ocean buoys that detect the tsunami and can be used to issue a warning. It's more difficult for local tsunamis because the time is, of course, quite a bit shorter. They can occur within minutes of the earthquake. That's why the recommendation is, if you're near the coast and you feel strong shaking, that you should move inland. 

5. If you do feel a quake, best head to high ground

A few years ago, there was a tsunami warning for parts of the California coast and so alerts went out. The recommendation was for people to be aware that the tsunami was approaching. And I think in this case, I think the expected tsunami was going to be relatively small but they encouraged people to stay away from the beaches and at lower lying areas, to move inland. 

For more information on the dangers faced in your area and evacuation procedures, visit the Governor's Office of Emergency Services website, MyHazards.