When a powerful earthquake off the North Coast generates a life-threatening tsunami, time will be of the essence for those in its path.
In the most serious scenarios, including the “big one,” a magnitude 9.0 megathrust event on the Cascadian Subduction Zone, waves could reach the shore in minutes, before any official alert would even be sent. And that’s if emergency systems are still working.
But Mother Nature has her own way of sounding the alarm — prolonged ground shaking that signals surges might be incoming and it’s time to move to higher ground, often just walking distance from most at-risk locations.
The key, local experts have long repeated, is knowing the local tsunami zones, places you’ll need to get away from — and to where — before a disaster strikes. When every moment might count, pausing to try to Google it out could take up the precious window of time to seek safety. Just as important is knowing when to stay put to avoid impeding emergency responses by clogging up traffic with unnecessary evacuations that might instead place you in harm’s way.
If reactions to the magnitude 7.0 earthquake in December of 2024 and ensuing tsunami warning are any indication of how well Humboldt County residents know what to do, there’s still some work ahead. Ditto for the confusion following alerts prompted by last summer’s magnitude 8.8 earthquake in Russia, which also could have been tamped down if more people had a solid understanding of the local hazard areas.
In a recently released report titled “The Next Wave in Tsunami Warnings in Humboldt,” the 2025-2026 Humboldt County Civil Grand Jury covers those points and offers some recommendations on “avenues that can be pursued that will reduce risks, save lives, educate the public and increase awareness of tsunami hazards in Humboldt County.”
“The biggest problem in Humboldt County is that many people are unaware of whether they are in a tsunami hazard zone at the time of an earthquake and potential tsunami, and they don’t have a plan regarding what to do,” the report states. “In times of high stress, signs and directions need to be clear about where to go or what to do to be safe. There are some relatively inexpensive and simple things that can be done to improve our tsunami preparedness and our responses during a tsunami emergency.”
While the grand jury focused much of its attention on the Eureka area, citing “limited time and the greatest risk being where tourists and populations are concentrated within the zone,” the report also encourages other Humboldt communities to consider some of the recommendations, including clearly delineating tsunami and safety zones on maps targeting visitors.
“Sirens were a mainstay for decades, providing audible alerts in the event of a tsunami. They are, however, extremely expensive. Newer technologies provide a cost-effective way to reach more people, while at the same time giving them more information than a siren alone could convey. ”
Humboldt County Civil Grand Jury report “The Next Wave in Tsunami Warnings in Humboldt”
Noting that local tsunami experts have long advocated for better preparation and outreach efforts, the report praised the city’s recent sponsorship of a tsunami preparedness workshop to help local businesses create emergency plans and a collaborative effort by the Ink People, Eureka Main Street, the Wiyot Tribe and the Eureka Cultural Arts District Leadership Council to create a tsunami art mural project in the Old Town area.
To further increase awareness, as well as guide out-of-towners and locals alike to safety, the report points to how other at-risk communities have employed “blue line” pavement signage, noting the street markings have proven to be “effective and economical in drawing public awareness to where safety lies in the event of a tsunami, providing quick, instantly understandable emergency directions and reducing risks.”
And, as mentioned above, the grand jury recommends the city update visitor and kiosk maps to include “color-coded tsunami hazard and safe zones,” calling the current absence of the information a “missed opportunity.”
The report also leans into the larger picture on the warning front.
In the realm of tsunami threats, as the grand jury noted experts they spoke with emphasized, there are two distinct types: near-source events with, again, prolonged shaking being the warning and waves potentially minutes away, and distance source, with hours of lead time and a variety of ways to get the word out. The Kamchatka quake is an example of the latter.
While tsunami sirens carry a certain cachet for many people, the reality is their use is limited and the sun has been setting on the region’s one-time stalwarts of sounding the alarm for years. Most have been rendered mute after two decades of standing watch in Humboldt’s notoriously harsh marine environment.
Meant to alert people who are outside in a long-distance event, the last time the sirens rang out in warning was following the March of 2011 earthquake in Japan. (Read more about Humboldt’s sirens in the Journal’s March 10, 2022, story, “Icons of Preparedness.”)
Citing a number of reasons, from the limited range of about 1 mile under ideal conditions and the estimated $60,000 to $160,000 replacement price tag for each one to the advancements in technology that provide faster and more detailed information, the report says, “The bottom line is that sirens are cost prohibitive and are unlikely to ever be installed here again.”
“Sirens were a mainstay for decades, providing audible alerts in the event of a tsunami. They are, however, extremely expensive. Newer technologies provide a cost-effective way to reach more people, while at the same time giving them more information than a siren alone could convey. “
With that said, the grand jury recommends the county’s Office of Emergency Services (OES) “further publicize that Humboldt County’s outdated siren system will not be replaced or expanded” by Tsunami Week in March of 2027.
“Historically, many residents of Humboldt County have relied on sirens to warn them of an approaching tsunami,” the report states. “But now, such reliance leads to a perilous assumption which can endanger residents.”
Turning to the technology side, the grand jury recommends the county’s OES “assess its current local wireless alert system for geolocation functionality” to send out more targeted information in case of a tsunami. That, the report states, could help alleviate panicked responses, like what occurred after national Tsunami Warning Center alerts, with the ominous “You are in danger” message, went out following the local magnitude 7.0 and the Russian quake, leaving some people well out of the hazard zone unsure how to react.
Lori Dengler, emeritus professor of geology at Cal Poly Humboldt, explained another complicating factor in her Not Your Fault column, cited in the grand jury report. Maps displayed on the center’s website showed weather hazard maps rather than Humboldt’s official tsunami zones in the latter case, resulting in some confusion about who needed to evacuate.
The grand jury recommends the county OES start using geolocation, if available, by March of 2027. Or, if it’s not, to “compare the current system to other systems which provide geolocation capability and evaluate available funding and submit a report” to the sheriff by New Year’s Eve.
The two recent events showcased the differences in the two types of earthquake-driven threats facing the North Coast and highlighted the importance of not only studying the local tsunami maps ahead of time but trusting where the lines are drawn.
That starts with visiting the Redwood Coast Tsunami Working Group website (at rctwg.humboldt.edu/tsunami-hazard-maps) to get a lay of the land. That means not just examining where you live but where you work, where the kids go to school or daycare and the places you go on a regular basis, says Ryan Aylward, warning coordination meteorologist with the National Weather Service.
“Look up all those things and then see, ‘Where would I have to go in that scenario, if a big earthquake happened when I was at that location,” he says.
“Then, in the moment, you’re not having to look that up. Because one, the internet might not be working. And it’s just once you know, you feel better about it. You know where to go. I always suggest practicing it — try walking out of the zone. You’ll see how easy and short it is for the vast majority of places in our area.”
Also, for those with children, now is the time to talk with their school about the onsite plan and how you will reconnect when the danger is over, Aylward says, noting campuses are “really safe places during these natural disasters.”
“You don’t want to go driving through the tsunami zone to get to your child when the tsunami wave is coming in; that’s a very bad outcome,” he says. “So, knowing all of this ahead of time is very important.”
In addition to looking up the maps online, people can also visit the RCTWG booth at the Humboldt County Fair this week or drop by the weather service office at Woodley Island anytime to get more information, Aylward adds.
One of the things he says he’s often asked about is what the yellow zones on the maps mean and the answer is simple: “That is the worst-case scenario, a 9.0 earthquake on Cascadia, where the tsunami wave could reach.”
It also takes into account the quake hitting during high tide and the ground subsiding across the coast, then adds 3 to 6 feet of vertical height onto the zone for extra layer of protection.
“It’s very conservative, is how we would describe it,” says Aylward, who was part of the team that designed the new maps released in 2021. “We are trying to keep people safe and so they know if they are in the green, they are outside of the zone.”
As the Journal reported at the time, the Dec. 5, 2024, quake on the Mendocino Fault was the first run of a tsunami warning being issued directly to cell phones through the Wireless Emergency Alert system, likely adding to some of the uncertainty of whether to stay or go.
“It goes back to personally understanding your own risk for where you are. If you don’t understand that, you are going to get an alert and it’s like, ‘What does that mean for me,’” Aylward says. “So no matter what, out of all this, you’ve really got to do some research ahead of time to understand the tsunami threat around here so that you’re not trying to figure that out in the moment because, for a local one, you’re definitely going to waste too much time trying to figure that out and you’re not moving.”
And moving, once safe, was exactly what people within the tsunami zone should have done on that day, he says, noting it was “a really long-lasting earthquake.”
“Here we clocked it at over a minute, I think it was a minute and a half, of just rolling shaking,” Aylward says. “For people, that should be your sign that this is something that could have produced a tsunami and some places reacted the right way. Like up at Manila School, they evacuated to high ground and they got there before the warning arrived.”
The warning was later canceled, but had the temblor struck on the Cascadia, the situation could have been different, Aylward says, pointing to the 1992 Cape Mendocino quake, a magnitude 7.2 produced when a small corner of the fault ruptured, sending a locally generated tsunami to shore.
While not causing full inundation of the yellow areas, he says even one 3-to 5-feet high could be dangerous for someone who’s near the coast. “So the threat was there, there’s no doubt about it. It’s just that, thankfully, it happened on a different fault.”
With the chances of a tsunami beginning to increase around a 7.1, Aylward says the national warning center has a default that any quake larger than magnitude 7.0 within a certain distance of the coast triggers a warning in the moment. The idea is to send out an alert quickly as a precaution to keep people safe, then further analyze the risk, which is what happened in December.
Next time, there may not be a warning other than from the ground under your feet.
The 10-minute timer for a tsunami to reach shore in a serious quake starts when the earthquake starts, he says, during the “big one” on Cascadia, that could mean five minutes of shaking. Meanwhile, Aylward continues, analysis at the Tsunami Warning Center takes about four to five minutes before they send an alert. By then, for those in the zone, the clock will already have been well into ticking.
“So no matter what, out of all this, you’ve really got to do some research ahead of time to understand the tsunami threat around here so that you’re not trying
Ryan Aylward, National Weather Service warning coordination meteorologist.
to figure that out in the moment because, for a local one, you’re definitely going to waste too much time trying to figure that out and you’re not moving.”
“You’ve got to get moving once it is safe to move,” he says. “And then after that, you are hopefully going to get follow-up information, if systems are working, about where the threat is and what the threat is and how long you are going to be staying out of the zone. For a local one like that, it could be 24 hours before you could ever go back in the zone. If it’s really the big one, it could be a very long time.”
Distance source tsunamis are when warning systems really have their day because there’s time before the wave arrives to get out and update information in an assortment of ways beyond the alerts, including media broadcasts and first responders closing off roads and driving through to warn vulnerable residents.
Still, the same general rules about knowing your zone apply.
In the Russian quake, for example, the event was expected to be below the warning level for Humboldt Bay and local beach areas, with the greater concerns for Del Norte County, which the NWS and county OES communicated at the time. Then later analysis by the Tsunami Warning Center indicated Trinidad might see larger waves and a warning was sent out to phones across the county even though threat levels in most areas didn’t change.
“You’re going to have more time to do an investigation [in a distance event], but you need to do that ahead of time so you don’t get too worried and too freaked out in the moment and then do something that puts yourself in danger more than where you are at that exact moment because the vast majority of people are actually safe and out of the zone most of the time here,” Aylward says.
As for the grand jury suggestion that county OES use geolocation, Aylward, speaking generally, says the weather service does that for events like severe storms, but it takes time to draw the polygons and cellphone towers might limit how targeted those can be.
Tsunamis are a bit different in that the areas needing to be alerted cover a wider range, which exceeds the system’s capability, he says, adding the weather service is looking for a workaround to focus tsunami alerts near the coast but for now the entire county is included.
“The message that comes from the Tsunami Warning Center goes straight to people’s cellphone,” he says. “It’s direct. It doesn’t go through the county. It doesn’t go through us at the weather office. It just goes directly to your phone countywide.”
At the end of the day, having a plan and understanding and trusting the local maps are the best ways to stay safe — and make good choices — in the event of the next earthquake like the one that hit on Dec. 5, 2024. Or an even larger one.
“I have kids in McKinleyville and, in that scenario, I immediately knew that I’m staying here. I know I’m safe here at the office, we are just outside the zone, I know my kids were safe at their daycare and school in McKinleyville, so I didn’t have to worry about them, and my wife was somewhere else, but she was also in a safe location,” Aylward says. “Everybody knew they were going to stay where they were until we had clearance that things were OK. So I didn’t have any worry in my mind about what was going on with them and that is the key. You don’t have to worry about it if you know what their plan is and what is going on. And then you don’t do something that you didn’t need to do.”
Find more information and see interactive maps on the Redwood Coast Tsunami Work Group website at https://rctwg.humboldt.edu/tsunami-hazard-maps.
Kimberly Wear (she/her) is the assistant editor at the Journal. Reach her at (707) 442-1400 ext. 105 or kim@northcoastjournal.com.
This article appears in ‘The Next Wave’.
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