Q&A: The 'Imperfect Science' Behind Tsunami Warnings

Brian Garcia, a warning coordination meteorologist for the National Weather Service based in Monterey, was in the East Bay on Thursday morning when an earthquake alert, then a tsunami alert, hit his phone.

He rushed to San Francisco’s Office of Emergency Services to confer with officials as they assessed the local threat from a 7.0-magnitude quake off the coast of Humboldt County. About an hour after the tsunami warning went out, it was canceled — but not before many coastal communities had already started evacuating people.

Garcia talked to KQED’s Dan Brekke about the reasons for the dire-sounding advisories issued by the National Tsunami Warning Center in Alaska and what officials hope to learn from the episode.

This interview has been edited for length and clarity. 

Dan Brekke: So let me ask you about the warning. The warning that went out from NWS Bay Area seemed to use very general but also very alarming language about the potential threat to life and property.

And I wonder if — given the reaction in the city of Berkeley for instance, where the warning prompted mandatory evacuations — was that an appropriate warning to put out there given the history of tsunamis in this part of the coast?

Brian Garcia: So the language that’s used in the Wireless Emergency Alert is a prescriptive language that goes out with all the warnings. And when we’re talking [about] a warning-level tsunami, we’re talking 3-plus feet of tsunami amplitude coming in, and in this scenario here, we were looking at an upcoming [high] tide as well — so that had been on top of the already increasing tide. So this definitely could have had some pretty significant consequences.

Anytime we’re talking about a warning, we’re talking a threat to life. Whenever we’re telling people to get out of harm’s way, that it’s a threat, immediate threat to their life, we’re not kidding. We don’t want to mince words in these situations. We want to make sure that people have the requisite information to get out of the way.

To what extent are you dependent on information from the National Tsunami Warning Center in Alaska? That’s one place I went to myself just to see if they had forecast any particular wave heights, and I never saw that they did.

The National Tsunami Warning Center is one of our centers under the National Weather Service umbrella, and we are wholly and completely dependent on them. They are the experts when it comes to tsunamis.

They are the ones actually, when they issue a tsunami warning, it triggers the Wireless Emergency Alert that hits your phones immediately from their office. So it doesn’t even come to our local office before it hits the Wireless Emergency Alerts across phones.

There was some estimate or projection out there that this event off the coast of Humboldt County could have created a wave height difference that would have been 3 feet above normal. Is that right? 

Anytime we have a warning-level event, that means that the tsunami amplitude is expected to be 3 feet or above. So today, for example, we were going to have a 5-foot high tide. That would have been our highest tide, but another 3 feet on top of that. So now we have an 8-foot water level compared to that normal mean low or low water datum that’s used for the tides.

I’ve been here since the mid-1970s, and of course, with large earthquakes around the Pacific Basin, tsunami warnings happen — they’re not unheard of. I have to say, in all that time, the one time that a perceptible tsunami actually showed up here in the Bay Area was, of course, in March 2011 after the earthquake off northeastern Japan.

I guess why I’m mentioning this is that when I heard the warnings and saw what the reaction was — the evacuation orders in Berkeley, for instance — I thought they were ridiculous. Am I wrong that the warning was overblown and really not consistent with our actual tsunami history, which includes lots of big earthquakes off of Humboldt County, by the way?

This is really an imperfect science in this type of scenario and trying to nail down exactly where it occurred, whether it was on the Gorda Plate or the Cascadia subduction zone.

In this event in particular, the earthquake location was close enough to the subduction zone that it created a risk, and we just weren’t willing to take that risk from the Weather Service side to say, “You know what, we’re going to wait and see a little bit more data,” because from that location, the travel time is in tsunami terms negligible to get potentially tens of thousands, if not hundreds of thousands of people out of harm’s way.

And so we want to make sure that our emergency management partners across the area can work with our local law enforcement to enact evacuations out of areas.

I know you’re kind of a buff of the history of tsunamis here, and in 1964 with the Alaska earthquake and tsunami we had impacts in bayside Marin.

So whenever we think of potential impacts for our friends and family and our residents around the Bay Area, we want to make sure that the information is clear … that they have something that they can say, “OK, there’s a tsunami warning, I’m going to get to high ground,” and they know that it’s only going to be a matter of a couple of hours because of the distance that the tsunami would have to travel in this scenario.

Today, for instance, what ultimately happened was as more data came in, it showed that [the earthquake epicenter] was actually on a strike-slip fault and we became more comfortable with saying that the odds of generating an appreciable tsunami are becoming less and less plausible. And all that is to say we’re always going to err on the side of protection of life.

Do you have any concern about people going through something like this, seeing that nothing happens, and then that desensitizes them to the danger the next time something like this happens?

Yeah, absolutely. There’s always the concern about desensitization to warning-level events. We see that in Tornado Alley when people get so many tornado warnings. The next one there, they’re just ignoring it because all the other ones before haven’t manifested in a tornado at their location. But that doesn’t negate our responsibility to issue the warnings based off the scientific data that we have at that time, and as soon as we know more data, we update that information.

What kinds of lessons might forecasters and local officials take from what happened with this warning? 

One of the things that we talk about often internally with the sciences and the response agencies is, you know, these things are now forefront of mind. We have our media partners doing stories on it. We have photos of kids on parking garages. We’re going to have a lot of after-action reviews and hot washes within these agencies, and we can’t let these events go to waste. We’ve got to look at them and say, “OK, what could I, as a resident of San Francisco or Berkeley or whatever, what could I have done different in this scenario? What do I need to be ready for, for the next one?”

So, if there’s one thing to learn from this, it’s what we say after every earthquake: Have a plan, have your go bag, have your kit ready to go at a moment’s notice, so that you can be ready for when the next one happens. We live in a dynamic environment. And we need to be ready for anything.