5 things Californians should know about tsunamis

Late Thursday morning, a magnitude 7.0 earthquake shook parts of Northern California, the shallow quake occurred 72 miles off the coast of Eureka and briefly prompted a wide tsunami warning. The tremors shook lights, sloshed pool waters onto land. Minor damage was reported on land.

The size of this quake and the wide tsunami warning had us going back to a question we explored the last time a quake of this magnitude hit off shore: What would it take for a tsunami to hit the California Coast?

To answer that question, we're revisiting an interview LAist did with Elizabeth Cochran in 2016. She's a seismologist with the U.S. Geological Survey.  She left us with these five takeaways:

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," Cochran explained, adding, "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

Cochran told us in 2016, when magnitude 6.5 earthquake hit 100 miles off the coast of Eureka, that the area was "fairly active for earthquakes."

That quake was felt justly slightly on land and did not result in a tsunami. But she cautioned, distance from land didn't mean the coast was safe.

"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," Cochran said. "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," she said. "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

Cochran noted that several factors go into when a tsunami hits ground.

"It depends how far away you are from where that earthquake occurs and where that tsunami is generated," she said. "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."

She said that the good news is there's a system in place to monitor ocean activity.

"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," Cochran explained. "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

Cochran said we should always take warnings seriously and to stay away from the beaches. If you ever feel a quake near the ocean, always move inland just to be save.. 

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

We have earthquake resources

We don't want to scare you, but the Big One is coming. We don't know when, but we know it'll be at least 44 times stronger than Northridge and 11 times stronger than the Ridgecrest quakes in 2019. To help you get prepared, we've compiled a handy reading list:

• Your guide to surviving the Big One
• For earthquakes, forget the 'go-bag.' Here's how to prepare
• How to not get life-threatening diarrhea after a major earthquake
• 10 earthquake-related questions to ask your landlord immediately
• How to prepare for an earthquake if you have a disability

Listen to our podcast