earthquake
DEFINITION: An earthquake is a term used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magnetic activity, or other sudden stress changes in the earth. (U.S. Geological Survey)
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HISTORY: In the past 150 years, nearly 40 earthquakes of magnitude 6 or larger have affected Northern California. (Earthquake Country Alliance)
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LOCAL EARTHQUAKES: Although infrequent, earthquakes of greater than magnitude 6 have occurred in Del Norte County, including a magnitude 6.9 that occurred in 1873, with impacts largely centered on the Smith River valley and Crescent City areas. (U.S.G.S.)
THE BIG ONES: The world's largest faults are associated with subduction zones. These faults are capable of producing earthquakes in the Magnitude 9 range. Del Norte County lies near the southern terminus of the nearly 700-mile long Cascadia Subduction Zone positioned just off of our coast.
Earthquakes on the Cascadia Subduction Zone are low-frequency, high-impact events. The last great Cascadia earthquake took place in the year 1700, a little over 300 years ago. Geologists have found evidence for at least 13 great Cascadia earthquakes during the past 7,000 years, and estimate they occur irregularly at intervals anywhere between 200-800 years apart. The next Cascadia earthquake could have local impacts similar to those experienced in Japan in 2011. It could cause strong ground shaking from Northern California to Southern Canada, lasting for five minutes or longer. It will also produce a tsunami with initial waves arriving onshore in Del Norte County in as few as ten minutes, and will not only affect our coast, but also the coasts of other countries throughout the Pacific basin. (Redwood Coast Tsunami Work Group)​​
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REGIONAL EARTHQUAKES: The Mendocino Triple Junction in Humboldt County has produced several large earthquakes, including a magnitude 7.2 in 1992, and a 7.0 in 2024. Depending on the location and direction of the rupture, an earthquake in this fault zone can not only cause shaking damage in Del Norte, but can also generate a tsunami that could arrive on our shores in as little as 15 minutes.
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Learn more about earthquake and tsunami risk on the North Coast by downloading the Living on Shaky Ground publication, now available in English and Spanish.
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WHAT TO DO
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RESPONSE ACTIONS: If you feel shaking or receive a notification of an earthquake in our area, immediately Drop, Cover (get under a sturdy table or desk, or duck and cover your head and neck with an object or your arms), and Hold on! Do not run outdoors, and do not take refuge in a doorway. If you are in the tsunami hazard zone, head inland or move to higher elevation on foot as soon as you can safely walk, taking care to avoid broken glass and downed power lines.
PREPARE: Simple mitigation measures in your home and workspace can make all of the difference between walking away from an earthquake unharmed and sustaining serious injuries. Find household mitigation tips from Cal OES here. Community members should prepare to be self-sufficient for up to two weeks after a major earthquake, without the benefit of running water or power, and without initial assistance from response agencies. View tips from the American Red Cross to prepare your household for a major earthquake and its aftermath. Develop a plan for your household that includes where you will reunite after an earthquake, and how you will contact each other.
​​​GET NOTIFIED: Earthquake Warning California is a publicly available, statewide earthquake warning system that could give California residents crucial seconds to take cover before shaking begins. The MyShake App is a free smartphone app available to iPhone and Android users that provides audio and visual warnings for nearby earthquakes of magnitude 4.5 or higher.
KNOW YOUR ZONE: Know in advance whether your home and the places you frequent are in the tsunami hazard zone. Find searchable interactive and printable tsunami hazard maps on the Redwood Coast Tsunami Work Group page.​
BE AWARE: Find information about recent earthquakes from the United States Geological Survey (USGS), or about tsunamis at the National Tsunami Warning Center (NTWC).​
REGISTER FOR COMMUNITY ALERTS: The Del Norte Community Alert System is an opt-in emergency notification system. Residents must register in advance to receive notifications. Register today to ensure you receive emergency information when you need it.​​​​
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GET INVOLVED: Practice your earthquake response during the annual Great California ShakeOut each October, and be sure to register to have your involvement counted!
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