Humboldt Bay Fire CERT

06/07/2026

Not My Fault in today's Times-Standard (6/7/26)
June earthquakes are a reminder that North Coast earthquakes come from different sources
Lori Dengler for the Times-Standard
Posted June 6, 2026
https://www.times-standard.com/2026/06/06/not-my-fault-june-a-reminder-that-north-coast-quakes-come-from-many-sources/

Image: June 3 earthquakes (orange circles) superimposed on a map of different sources of strong earthquakes in the North Coast region from a paper by Dengler, Carver, and McPherson published in 1992. The M5.7 earthquake was on a fault within the Gorda plate far offshore of Del Norte County. The M5.1 was on the Mendocino fault and likely an aftershock of a December 5, 2024, M7.0 quake. ....................................
Early Wednesday morning June 3, several earthquakes struck the North Coast region. I didn’t feel them, but others did. A M5.7 far struck far offshore of the CA – OR border a little before 4 AM and a M5.1 offshore of Cape Mendocino occurred a little under two hours later. The earthquakes were not large enough and too remote to cause any damage but are a reminder that we live in earthquake country and have numerous fault sources that can cause potentially damaging earthquakes.

The first earthquake occurred at 3:53 AM PDT and was centered 104 miles WNW of Crescent City. It was a shallow earthquake, less than 10 miles beneath the sea floor on a strike slip fault within the Gorda plate. The Gorda plate is the southernmost part of the Juan de Fuca plate system and the source of many of our strongly felt earthquakes. The slip on the fault was entirely horizontal and likely oriented in a NE – SW direction.

The USGS issued a ShakeAlert 29 seconds after the earthquake with an initial magnitude estimate of 5.2. ShakeAlert currently operates in the three West Coast states and is being expanded into Nevada. Utilizing a dense network of on shore seismic stations, it automatically locates, estimates magnitude, and forecasts likely shaking strength within seconds of the fault rupture initiation. The offshore location and moderate magnitude showed no coastal areas likely to feel moderate shaking, so the alert was not sent to cell phones through the Wireless Emergency Alert (WEA) system.

Five minutes after the earthquake, the National Tsunami Warning Center (NTWC) in Palmer Alaska sent out a Tsunami Information Statement that the earthquake was too small to cause a noticeable tsunami. Their magnitude estimate was 5.7, identical to the final USGS magnitude that was confirmed a few minutes later. Information statements are the most common bulletins issued by NTWC, usually explaining that an earthquake has occurred, may have been felt, but was either too small or too deep to produce a noticeable tsunami.

The M5.7 was noticed by some people on the Northern California and Southern Oregon coast. Thirty-five people filed felt reports on the USGS “Did You Feel It?” web site, most between Crescent City and Reedsport. I’m suspicious of a few of them, it’s highly unlikely that it was felt by anyone in Fresno, and I think a few of the reports from the Humboldt County were likely confused with the second earthquake that occurred just under two hours later. No aftershocks have been recorded to date, although the USGS still estimates a one in five chance of an M3 event in the next week.

There is nothing unusual about the 5.7. Eight earthquakes in the magnitude 5 range have occurred in this part of the Gorda plate in the past five years and 35 since 1980, the largest a 7.0 in August 1991. Our largest North Coast quake of 2025 was a 5.7 50 miles NW of Wednesday’s tremor. Although not as common as earthquakes in the southern part of the Gorda plate, they are not infrequent, and we can expect them to continue in the future. Their remote offshore location makes them unlikely to be felt by many or cause damage, but a repeat of the 1991 M7.0, especially if nearer to the coast, could cause damage in Del Norte County and would likely trigger a tsunami warning for the region, even though the tsunami potential of strike-slip earthquakes is small.

Earthquakes in the Gorda plate are driven by regional tectonic stresses. To the north, the main part of the Juan de Fuca plate is slowly spreading out from the Juan de Fuca ridge and moving in in a southeast direction relative to the Pacific plate, exerting a very large force on the much smaller Gorda plate. The Gorda plate can’t move out of the way because it is constrained by the enormous buttress of the older, colder Pacific plate south of the Mendocino fault and the North American continent to the east. The only response is to “crack” under the pressure, resulting in the numerous faults and moderate to large earthquakes in the interior of the plate.

An hour and fifty-two minutes after the Gorda plate 5.7, an earthquake occurred on the Mendocino fault, 120 miles SSE of the earlier earthquake. ShakeAlert issued a message 14 seconds after the earthquake with an initial magnitude of 4.2, not large enough to trigger WEA alerts to cell phones. The NTWC issued a tsunami statement six minutes after the earthquake notifying us that a M4.9 had occurred, and no tsunami would be generated. A few minutes later, the USGS updated the magnitude to 5.1 with a location on the Mendocino fault, 39 miles west of Petrolia. Fault analysis shows purely E-W horizontal slip, consistent with the orientation of the Mendocino fault.

The 5.1 was felt more widely than the earlier M5.7. The USGS “Did You Feel It?” site includes 121 credible felt reports from Westport in northern Mendocino County to McKinleyville. No one reported any damage. Seven aftershocks have been recorded to date, including a 4.5 at 6:11 AM, a 4.0 at 8:51 AM and a 4.5 at 7:36 PM all on June 3 and reported felt lightly. The USGS gives a 28% likelihood of more aftershocks in the M3 range over the next week.

Earthquakes are common on the Mendocino fault, the transform plate boundary between the Gorda plate to the north and the Pacific plate to the south. It is one of the most active fault systems in the lower 48 states in terms of earthquake production. Wednesday’s 5.1 was centered almost on top of the epicenter of the December 5, 2024, M7.0 and is likely an aftershock of that event. Seismic activity in the aftershock zone had quieted over the past six months, but it’s not unusual for spurts of activity to occur years after earthquake of this size. The USGS aftershock forecast of the 2024 quake still gives a 14% likelihood of another M5 in the next year.

Two earthquakes less than two hours apart might make you think they are related, and they are, but only in the general way of responding to the regional tectonic stresses. The offshore Crescent City and the Cape Mendocino earthquakes have no direct relationship. They were in distinctly different tectonic environments, and it was only coincidence that they occurred so closely together in time.

This isn’t the first time we’ve seen different source areas in our area set off quakes so close together. On August 16, 1991, a M6.1 earthquake occurred in the Gorda plate 24 miles SE of Wednesday’s 5.7. Twenty-one hours later, a M6.0 occurred in Honeydew 130 miles away. Three hours after the Honeydew earthquake, a M7 occurred near the location of the 6.1. No question that the 6.1 and 7.0 were related. They were centered only two miles apart and had the same type of fault orientation and slip. But Honeydew was a thrust earthquake in the triple junction area and likely related to the Cascadia subduction zone. It was pure coincidence that these two different areas had earthquakes at the same time.

I’ve been thinking about source areas of North Coast earthquakes for a long time. In 1992, along with co-authors Gary Carver and Bob McPherson, we summarized our thoughts on all of the different potential fault systems and tectonic regimes that could cause large earthquakes. We came up with five distinctly different regions: the Gorda plate and the Mendocino fault active this week, the San Andreas fault, shallow faults in the North American plate, and the Cascadia subduction zone.

Our 1992 paper still holds up pretty well, and those five regions are still our primary source candidates. But it’s time to update that paper with everything new we’ve learned in the 34 years since it was published. At the time, we thought the 1954 Fickle Hill earthquake might have been on a North American plate fault. A re-examination surprised us all by likely putting it on the subduction zone interface, so we still have no recent examples of an earthquake on any of our mapped surface faults. We will add a “downslab tension” region just inland of the coast on north-south oriented normal faults. Two moderately deep mid M5 earthquakes in the early 2000s range likely caused by stretching of the subducting slab. We knew about these earthquake before, but they had all been smaller. And we need to expand our Gorda plate seismicity zone all the way west to the Gorda ridge as the whole Gorda plate is capable of producing earthquakes.

My big project for the next year is to update the ’92 paper and call on better brains than mine to rethink how these regions are interconnected.

Note: Our 1992 Sources of North Coast Seismicity paper is athttps://kamome.humboldt.edu/sites/default/files/Sources%20of%20North%20Coast%20Seismicity.pdf
-----------------------
Lori Dengler is an emeritus professor of geology at Cal Poly Humboldt, and an expert in tsunami and earthquake hazards. The opinions expressed are hers and not the Times-­Standard’s. All Not My Fault columns are archived online at https://kamome.humboldt.edu/taxonomy/term/5 and may be reused for educational purposes. Leave a message at (707) 826-6019 or email [email protected] for questions and comments about this column or to request copies of the preparedness magazine “Living on Shaky Ground.”

06/03/2026

Some of you may have gotten ShakeAlert messages early this morning. A few people on the Del Norte and Curry County coast were notified of a M 5.7 offshore of the CA-OR border at 3:53 AM PDT centered 104 miles WNW of Crescent City. It was reported felt by a few from Scotia to Reedsport. ShakeAlerts were also issued after a M5.2 earthquake occurred on the Mendocino fault at 5:53 AM PDT 40 miles W of Petrolia. That earthquake was felt lightly from Westport to Brookings and was followed by a M4.5 26 minutes later that was also felt lightly by some in Humboldt County. These earthquakes were not directly related, the first was in the Gorda plate near an area where a number of earthquake in the M5 range have occurred in the past year and the second was on the Mendocino fault and arguably an aftershock of the December 5, 2024 M7.

06/01/2026

05/29/2026

CERT Basic Training June 26-28, 2026. See flyer and QR code for registration. Host by Blue Lake Rancheria Resiliency Training & Innovation Center (RTIC) at Blue Lake Rancheria

05/19/2026

Heads up, Humboldt! The Humboldt County Department of Aviation would like to inform the community that Humboldt Bay Fire will hold a multi-casualty incident training exercise on Thursday, May 21, from 10 a.m. to 1 p.m. The exercise will take place at Murray Field Airport, located on Airport Road in Eureka. ✈

The training exercise will simulate an airplane crash with multiple casualties, giving Humboldt Bay Fire firefighter/EMTs and firefighter/paramedics the opportunity to practice mass casualty response, practice executing the North Coast Emergency Medical Services (EMS) Multi-Casualty Plan, perform triage and set up on-site treatment areas. In addition, Humboldt Bay Fire will work closely with local ambulance companies and Providence St. Joseph Hospital to coordinate the rapid transport of "injured" patients to area hospitals.

This exercise is necessary on an annual basis for Providence St. Joseph Hospital to maintain its designation as a local trauma center.

𝗪𝗵𝗮𝘁 𝘁𝗼 𝗘𝘅𝗽𝗲𝗰𝘁
During the exercise, airport visitors, Highway 101 travelers and those in the vicinity of Murray Field should expect to see emergency fire vehicles, ambulances, EMS aircraft and emergency personnel operating within a controlled area on airport property.

There are no planned street closures, and airport operations will not be impacted as a result of this training exercise.

The County of Humboldt’s Aviation Department is proud to partner with Humboldt Bay Fire to provide a location for this important training opportunity. For more information on the Humboldt County Department of Aviation, please visit FlyACV.com.

For more information on Humboldt Bay Fire, visit HBFire.org.

📸 Pictued: An aerial view of Murray Field Airport, courtesy of the Humboldt County Department of Aviation. Additional text reads "County of Humboldt press release."

Fly ACV
Humboldt Bay Fire
Providence Humboldt County

05/15/2026

Tonight 1930 hrs on FWRA

05/13/2026

Narcan Train the Trainer event is available to all local teams. Pre-registration required, see flyer for more details.

04/29/2026

Near-source earthquakes can trigger tsunamis in minutes. Sirens may not sound—strong, sustained shaking is your warning. Move to high ground immediately.

04/28/2026

Emergencies don’t come with warning, and when they happen, you may be on your own for the first 72 hours or longer. Taking a little time now to put together a simple go bag can make a big difference for you and your family when it matters most. Having essential supplies ready to grab and go helps reduce stress, speeds up evacuation, and allows first responders to focus on the most critical needs in the community. Take a few minutes this week to get prepared!

04/26/2026

Not My Fault in today's Times-Standard (4/26/26)
April’s 1906 and 1992 earthquakes and the triple-junction connections
Lori Dengler for the Times-Standard
Posted April 25, 2026

Image: A tale of two earthquakes 86 years apart. The left shows Ferndale’s General Mercantile in the early morning hours of April 18, 1906, after the San Francisco earthquake (photo by Edna Garret from the Peter Palmquist collection). Right is the same brick building, renamed the Valley Grocery, on April 25, 1992, when it experienced similar damage in the Cape Mendocino earthquake (Kevin Bayless photo). It was torn down after 1992 and replaced with a wooden structure...............................
https://www.times-standard.com/2026/04/25/lori-dengler-aprils-1906-1992-earthquakes-and-the-triple-junction-connections/

Our last three significant North Coast earthquakes all occurred in December. Thist was mere coincidence and there is nothing about any particular time of year that is more earthquake prone. The two most damaging North Coast earthquakes in the era of instrumental records happened in April. This weekend is the anniversary of one of them and last weekend marked the other. They deserve a closer look.

I write about the April 25 – 26 1992 Cape Mendocino earthquake sequence almost every year to mark its anniversary. The only earthquake to merit a Presidential Disaster declaration, it caused more than $60 million in damages and injuring over 400. The April 1992 mainshock also caused a modest tsunami and was one of the driving forces behind the creation of the National Tsunami Hazard Mitigation Program.

Anyone who was on the North Coast in April ‘92 remembers what they were doing when the first earthquake struck at 11:06 AM on Saturday. It was a sunny day, and I was upstairs making final preparations for a family picnic. No cell phone alerts in those days, and the rumble and the shaking caught me by surprise. I gathered my wits and remembered to start counting. After years of recommending that others do so in earthquakes, this was this first time I succeeded in doing the same. The effect was instantaneous, slowing the adrenalin rush and allowing me to observe what was happening. My count lasted 45 seconds, only the first 20 or so strong, the last part barely discernable. I guessed at least a mid-6 but too rolling to be right underneath me.

Afterwards, I headed downstairs and we gathered outside. I lay down on the lawn to better feel any aftershocks and was rewarded with several tickles - an earth massage. Neighbors were outside too, all discussing what had just happened. One item had tipped over on a counter, but our home was spared damage, and we smelled no gas so we could safely leave the gas line open. It’s important to know how to turn off your gas line but doing so means only trained PG&E service personnel can turn it back on and probably several days delay. No smell means no leak so just leave it be.

No picnic for me that day. Internet was in its infancy and communicating with colleagues meant lots of phone calls. Fortunately, land lines and power stayed on in most of the county. A number of Humboldt Geology faculty and students headed into the field to look for signs of liquefaction, landslides, and fault rupture. I played coordinator with field groups and other researchers planning instrument deployments.

There was no tsunami alert that morning. The preliminary magnitude was 6.9, just under the M7 threshold in place at the time, and none of us thought about tsunamis in those days. It took our very sharp State Geologist at that time Jim Davis to query NOAA and the tsunami warning centers to see if a tsunami had been triggered. We had the same number of tide gauge stations on the California coast as we do now, but none were online, and it took several days for the records to be retrieved. We were all surprised to see the 8-inch-high squiggle from the Humboldt Bay tide gauge and an almost two-foot tsunami in Crescent City. It was low tide and only a few people reported seeing anything unusual.

We take it for granted that a preliminary magnitude and location for any felt earthquake will be available within a minute or two and a tsunami assessment soon after. In 1992, it took about three hours to get accurate earthquake information. But like today, the best source of information on the impacts was the radio and I would channel surf to get updates on what eyes on the ground were seeing. I also had a student Kevin Bayless with emergency response contacts, and I sent him off to photograph as much of the epicentral region as he could.

There would be no sleep for me that night or for many other North coast residents. Two large “aftershocks” would cause additional damage at 12:48 AM and 4:18 AM. My counting (35 and 40 seconds respectively) suggested they weren’t quite as large as the earlier earthquake but still packed a major punch. I put aftershock in quotations because they were both on different faults and nearly as large as the first quake. Some seismologists prefer to call them ‘triggered’ earthquakes, but I use aftershock to mean any quake clearly related in time and space.

It would take months for seismologists to analyze these earthquakes. The April 25 quake ended up as a magnitude 7.2 and the early morning quakes a 6.5 and 6.6 respectively. The mainshock was shallow by North Coast standards, only 6 miles deep and centered on a north-south thrust fault closely associated with the Cascadia subduction zone. The latter quakes were about 18 miles away offshore, more than twice as deep with horizontal movement (strike-slip) within the Gorda plate. The third largest aftershock occurred ten days later, centered just south of Cooksie Mountain and seven miles south of the mainshock. It was a shallow strike-slip quake and probably in the North American plate. There were plenty of smaller aftershocks on the Mendocino fault too. This was truly a triple junction sequence with faults within and bordering all three plates (Pacific, Gorda, North America) that abut near Cape Mendocino participating.

Last Sunday’s paper featured a page on the second notable April quake, the April 18th, 1906 “San Francisco” earthquake. I put San Francisco in quotations because it is misleading. It is protocol to name earthquakes after a city, town, or geographic feature closest to the epicenter. While the 1906 epicenter was just offshore of San Francisco, the rupture was very long, extending 200 miles north to Cape Mendocino and 60 miles south to Santa Cruz. This entire fault rupture was the source of seismic waves and the Eel River Valley experienced shaking just as strong as San Francisco.

From a Humboldt County perspective, last Sunday’s overview of the 1906 earthquake omitted the most interesting part of the story – the devastation it caused here. I spent much time in the early 2000s pouring through newspaper archives and reports on the 1906 earthquake to map out the shaking strength in more detail. My research led me to photo historian Peter Palmquist who had collected historic photos with a particular emphasis on early women artists. He introduced me to the work of Edna Garrett, a photographer who with her husband had a studio in Ferndale in the early 20th century.

Like everyone in Ferndale, Edna was rudely awakened at 5:12 AM on April 18th. Unlike her husband or the other two men who had Ferndale photography studios, Edna immediately grabbed her camera and equipment and set about documenting the impacts in Ferndale. Because of her work, we have a detailed record of what happened to nearly every building on Main Street and the earliest imagery of liquefaction on the banks of the Eel River. See links below for more on the Humboldt County 1906 story.

Seismology was in its infancy in 1906 and there were no instruments on the North Coast. But the geology community was active and three days after the earthquake, Governor Pardee commissioned a detailed study of the geology, seismology, and impacts of the earthquake. Led by Berkeley Professor Andrew Lawson, 25 principal scientists and nearly 300 other professionals contributed to the study which is still considered the most thorough post-earthquake examination ever published. It took two years for field teams to map fault rupture, landslides, and document intensity from Humboldt to Santa Cruz counties. The elastic rebound theory of earthquake genesis was one of the results.

There is no question that the 1906 earthquake caused a much larger swath of damage in Humboldt County than any more recent temblor. I used reports of chimneys fallen to map out the intensity VII and stronger zone of shaking and compared it to what happened in 1992. The 1906 zone was about twice as large, extending as far north as Blue Lake and east to Bridgeville. Not only was the area of 1906 damage larger, liquefaction was far more pronounced in 1906 with surface water expelled from the shaking making it difficult to travel from Eureka to the Eel River Valley for many days.

The largest 1906 aftershock occurred on April 23, five days after the mainshock. It was offshore of Trinidad, likely in the Gorda plate, roughly 50 miles north of the northern termination of the 1906 rupture. Like 1992, this was another “triggered” earthquake. Models of 1906 suggest that some of the largest slip occurred at the northern end of the rupture zone with the western or Pacific side of the San Andreas moving 18 feet north relative to the eastern North American side. This instantaneous ramrod affected stresses in the Gorda plate.

New quakes and old ones both tell us more about connections within and across the triple junction region. When one side gets tweaked, expect another piece to adjust. !992 and 1906 were very different earthquakes in scale and impacts but both reveal earthquake vulnerabilities and the necessity of planning for not just one type of event but many, possibly only minutes apart.

My paper on the 1906 earthquake on the North Coast is posted at https://kamome.humboldt.edu/sites/default/files/The_1906_Earthquake_on_Californias_North_Coast.pdf, a virtual field trip of the 1906 earthquake in Ferndale is at http://ebeltz.net/fieldtrips/1906quake-fdale.html
-----------------------
Lori Dengler is an emeritus professor of geology at Cal Poly Humboldt, and an expert in tsunami and earthquake hazards. The opinions expressed are hers and not the Times-­Standard’s. All Not My Fault columns are archived online at https://kamome.humboldt.edu/taxonomy/term/5 and may be reused for educational purposes. Leave a message at (707) 826-6019 or email [email protected] for questions and comments about this column or to request copies of the preparedness magazine “Living on Shaky Ground.”