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Anniversary of the Great Humboldt County Earthquake of 1923

January 19, 2023

On January 22nd 1923, a M7.1 Earthquake struck near Cape Mendocino in Humboldt County, California

One hundred years ago, a powerful magnitude 7.1 earthquake struck near Cape Mendocino and caused strong shaking and multiple aftershocks in Ferndale, Eureka, Petrolia, and many other communities in Humboldt County. The quake struck in the early hours of January 22, 1923 and was strong enough to knock down chimneys, split one home in half after shaking it from its foundation, and create a small tsunami. Shaking was felt hundreds of miles away in San Francisco and Sacramento.

M7.1 Earthquake struck in the early hours of January 22, 1923 and was strong enough to knock down chimneys, split one home in half
This Long Beach home—built in a similar style to many in Humboldt County—was damaged in a 1933 earthquake.

Humboldt County has had many large earthquakes in its History

Anniversaries like this remind us that Northern California is earthquake country and has a long history of powerful quakes. In fact, there have been over 40 earthquakes at or above magnitude 6.0 in the last hundred years in and around Humboldt County—and scientists continue to closely watch seismic activity in this region. Keith Knudsen, Deputy Director of the USGS Earthquake Science Center, once said “This area is the most seismically active part of California."

40 earthquakes at or above magnitude 6.0 in the last hundred years in and around Humboldt County
Each circle represents an earthquake in the past century at or above magnitude 6.0 within or near the region of the Mendocino Triple Junction.

The December 20th, 2022 M6.4 Earthquake near Ferndale, California

Although it happened a century ago, the widespread damage caused in 1923 will sound all too familiar to today’s Humboldt County residents; fireplaces and chimneys destroyed, water mains broken, windows and glass shattered, buildings shaken off their foundation or even shaken apart. Of course, we are reminded of the recent magnitude 6.4 earthquake just last month on December 20th, 2022 near Ferndale, CA. This quake occurred in the same region, known as the Mendocino Triple Junction, and was caused by a strike-slip fault, probably within the Gorda Plate. That large earthquake injured 17 people, damaged roads, homes, and utilities, according to the Humboldt County Office of Emergency Services. 12 days later, on New Year’s Day, a significant magnitude 5.4 aftershock struck the same area. It is estimated that over 90 homes were damaged so badly, they were “red-tagged,” or declared by authorities to be unsafe to live in.

December 20th, 2022 M6.4 Earthquake near Ferndale, CA in Humboldt County, California
This Shakemap from the December 2022 Ferndale quake shows the severity of shaking in the region.

What is the Mendocino Triple Junction? Why have there been so many earthquakes in Humboldt County?

But what exactly is the Mendocino Triple Junction, and why are there so many earthquakes in that area? Three tectonic plates (the Pacific, North America, and Juan de Fuca/Gorda plates) and three major faults (the San Andreas, Cascadia Subduction Zone, and Mendocino Fracture Zone) all meet at the Triple Junction, making earthquakes extremely common in the region. The Gorda plate, itself under intense tectonic pressure, is colliding with and being driven underneath the North American plate, creating the Cascadia Subduction Zone. This zone can generate an earthquake of a magnitude 9 or larger, occurring—on average—once every 500 years. The last quake that big was in 1700. All of this means that earthquakes will continue in the region for a long time to come.

Mendocino Triple Junction Fault Lines - North American Plate, Pacific Plate, Juan de Fuca/Gorda Plate
An illustration of the tectonic plates and fault lines that make the Mendocino Triple Junction a hotspot for earthquakes.

What are the Chances of a Major Earthquake in Humboldt County?

In 2014, scientists predicted there was a 76% chance that a magnitude 7.0 or greater earthquake would strike the North Coast of California within the next 30 years.

Whether looking at quakes past, present, or future, we are reminded that Humboldt is especially vulnerable to earthquake damage, and it's important to be prepared. Learn how personal preparedness and practicing critical steps to safety can help you be ready. One of the best ways to protect your home and family may be to strengthen your home with a seismic retrofit before the next big earthquake strikes. Earthquakes strike with little warning—this step can help prevent damage and protect your home, especially if it was built before 1980.

Learn more: StrengthenMyHouse.com.



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