Brace Yourselves!

A Comprehensive Guide to Seismic Hazards in Humboldt County

By: Griffin Mancuso

At 2:34 a.m. on Dec. 20, 2022, McKinleyville resident Emily McCollum was rudely awakened by a violent shaking. McCollum had experienced earthquakes before and expected it to be brief. Unfortunately, this was not the case. As the shaking grew worse, all she could think to do was cling on to her bed for dear life. The click of her space heater told her that the power had turned off, and it would remain that way for the next 24 hours. Her home swayed back and forth, which was exacerbated by her living on the second story. She hoped her body wouldn’t be found in a pile of rubble. “No one ever talks about how loud earthquakes are. They’re loud,” said McCollum. “All the car alarms started popping off … and then it was eerily quiet once it stopped.”

In a panic, McCollum started pacing around her residence, picking up things in her living room that had fallen out of place and putting fallen photo frames back on the wall. McCollum then called her friends to make sure they were okay, and thankfully they were. Somehow, she was able to fall back asleep.

When she woke up, she was disappointed that all the food in her fridge had spoiled. With no access to electricity, she arranged a “power outage kickback” with friends. They recollected their experiences with the earthquake and played Cards Against Humanity. “It just kinda made it fun and easier for me to process, because it was so traumatic,” said McCollum. Along with McCollum, many residents of Humboldt County were left emotionally shaken by the event.

McCollum had no idea how frequent earthquakes occurred in Humboldt County when she moved here. After experiencing such a significant natural disaster, does she feel more prepared for potential earthquakes in the future? She said, “Hell no!”

The Triple Junction

Robert McPherson was a Senior Seismologist for TERA Corporation when he ran the Humboldt Bay Seismic Network and is currently a research associate for Cal Poly Humboldt. According to a workshop he attended, “Of all places in the United States, this is the most likely place to have an earthquake.” Humboldt County sits at the intersection of several major faults: the Cascadia subduction zone, the Mendocino fault, and the infamous San Andreas fault.

The Cascadia Subduction Zone is about 621 miles long and runs from Northern Vancouver Island in Canada to Cape Mendocino in California. It is comprised of the Juan de Fuca plate and North American plate. The Juan de Fuca plate pushes against the North American plate and eventually moves underneath it. The friction from this movement builds up over time until the faults’ rock slips past each other, resulting in a “megathrust” earthquake. Cascadia Subduction Zone earthquakes occur very infrequently (the last one took place in 1700), but great subduction zones are the only faults that can generate an earthquake above an 8.5 magnitude. This is the big one that most northern Californians are worried about. Historically, this zone has caused an earthquake every 400 to 600 years, but an earthquake could always happen outside of that average.

The San Andreas fault and the Mendocino fault are “strike-slip” faults, where the two plates slide past each other. The San Andreas fault stretches through western California, stopping roughly 30 miles short of Eureka. It is responsible for the 1906 and 1989 earthquakes in San Francisco, and is one of the few faults you can see from above ground. The Mendocino fault is a 162-mile long structure in the Pacific Ocean east of the North American plate. It sets a boundary between the Pacific Plate to the south and the Gorda plate to the north. It also connects with the Cascadia subduction zone to the east. The fault is active, but the recurrence of its earthquakes are unknown.

A Headache-Causing Fault

Along with these major faults, there are many smaller faults running through Humboldt County, with the Little Salmon fault being one of the more active ones. The Little Salmon fault runs through the dunes in River Valley, Hydesville, Fortuna, and southern Eureka. “It’s a fault that’s also caused some headaches because it was discovered after things were built on it, so that’s why some of the buildings on the College of the Redwoods campus aren’t allowed to be occupied, because they’re right on the Little Salmon fault,” Michalak said. “Nonetheless, an earthquake on it would be felt widely in this area. It would be very strong, similar types of magnitudes from the Rio Dell earthquake, and that’s a fault we know about.”

Early Earthquake Warning

Currently, the field of geology is focusing on earthquake early warning (EEW) systems. The goal of an EEW system is to give citizens as much time as possible to prepare for incoming tremors. Ideally, these systems should give people ten seconds of notice before the more damaging waves, the s-waves, start happening. This does not sound like a lot of time, but ten seconds can be the difference between life and death. Currently, McPherson is assisting in the improvement of Humboldt County’s early earthquake warning system. Both California Polytechnic State University, Humboldt and the United States Geological Survey have been contributing to a system of fiber optic cables to improve the EEW. The speed at which fiber optic cables move information will be able to better keep up with the earth’s speed of processing information, approximately the speed of, “a missle—8 km a second or something like that,” according to McPherson.

Worrying Waves

What about tsunamis? The largest recorded tsunami in history peaked at 1,720 feet in Lituya Bay, Alaska in 1958. A member of the California Geological Survey and adjunct professor in Cal Poly Humboldt’s geology department, Dr. Jason R. Patton, said it would take about a 7.2 magnitude earthquake to generate a tsunami. How far you need to travel above sea level will depend on where you live. “In some places, the wave will get higher than in other places. Because what happens is as the tsunami travels over land, it can slow down. So the same tsunami in Arcata won’t get to the same height as where I live in Manila,” said Patton. They recommended for Hum- boldt citizens to check tsunami.ca.gov to check where nearby tsunami hazard areas are so they can act accordingly. The main goal is to travel from within that hazard zone to outside of it.

Can We Predict Earthquakes?

Unfortunately, there is no guaranteed method of earthquake prediction at this time. Earthquakes are, currently, very difficult to predict with accuracy. Seismology developed as a science in 1889, so it’s just over a century old. The Earth, in comparison, is around 4.5 billion years old, so geologists have a lot of catching up to do. In fact, the fault that caused the earthquake in December, 2022 hadn’t been discovered until after the fact because it was not visible from the surface. New faults are constantly being discovered, especially in Northern California. “There’s lots of faults we know very little about. We don’t know their history, their characteristics, we know that we can see them, we really don’t know their capabilities. Oftentimes earthquakes are on faults that we never even knew about. We have a lot to learn. We are nowhere near ahead of the information; we’re way behind,” said McPherson.

So What Do We Do?

Earthquakes are going to happen whether we like it or not. Sometimes we won’t even notice them, and sometimes they rouse us from our sleep and send us running (or driving) for the hills. Instead of fearing when the next “big one” may occur, it’s important to learn from our younger generations. Michalak has experience teaching elementary school children about earthquakes, who she described as, “naturally curious”. Their first reaction to learning about earthquakes is, ‘That’s cool!’ rather than shutting down and saying, ‘That’s scary, I don’t wanna hear about that, I hope that doesn’t happen.’” Another advantage that these children have in a school environment is regular earthquake drills. “Earthquake drills are a great way to train your body and your mind to react when an earthquake happens. Sometimes adults don’t practice, so they don’t have that response,” Michalak said. Preparing for what might happen after an earthquake is just as important as preparing before it. The effects can be devastating, both in the short and long-term. Adrienne Newby resides in Loleta, but travels to Rio Dell to work at her father’s pizza restaurant. Even though Loleta experienced minimal damage compared to Rio Dell, Newby still found herself stranded.“It was hard for some people, especially when the power was out … [there is no] communication or knowledge of what’s going on. The power’s out, we have no internet. And I don’t have good data reception up there and I ended up stuck with no gas in Fortuna overnight, waiting for a gas station to open” she said. The restaurant, like many businesses there, was forced to shut down after the earthquake. Walking through the restaurant, you can see displaced tiles and cracks running along the ceilings and walls. Tables are moved into corners and decorations are taken down. The only reminder of the restaurant’s previous life is the menu hanging above the front counter. They were forced to close permanently on February 11.

While Humboldt County is an area with a lot of seismic activity, geologists are working with communities to better prepare for the future. Building codes are continuously improving, new technology is being researched, and earthquake prediction may one day be possible. Humboldt’s residents are not completely powerless. They can utilize the plethora of resources that geologists have created for them, connect with their communities, and continue to learn while they grow more familiar with the earth they live on.