Earthquakes: tidbits we need to know. When the ground beneath our feet suddenly shifts, it’s a stark reminder that Earth is a dynamic planet constantly in motion. Earthquakes occur far more frequently than most people realize, and understanding their patterns can help us better prepare for these natural events. If you live in the United States or are simply curious about seismic activity, here’s what you need to know about how often earthquakes shake American soil.
Here in the Salt Lake City, Utah area, we’ve had two small earthquakes in the past couple of weeks. Each one was in the 3 – 3.5 range and did very little damage, although many people reported feeling the quake. There is a fault line close to the Wasatch Mountains here that is pretty active. Those familiar with the frequent earthquake activity and the potential for significant damage to life and property often tell us that the “big one” is overdue and that we should do our best to prepare. This recent local activity is what prompted me to write this timely post.
How Often Do Earthquakes Actually Occur?
The frequency of earthquakes might surprise you. According to the United States Geological Survey (USGS), several million earthquakes occur worldwide each year. However, the vast majority are so small that people don’t feel them. These micro-earthquakes are only detected by sensitive seismographs positioned around the globe.
In the United States, thousands of earthquakes occur annually. The exact number varies from year to year, but on average, the country experiences approximately 20,000 to 30,000 earthquakes per year, including all magnitudes. Most of these are minor tremors that go unnoticed by the general population.
Breaking Down Earthquake Frequency by Magnitude
Understanding earthquake frequency becomes clearer when we look at the numbers by magnitude scale:
Small Earthquakes (Magnitude 2.5 or Less)
These earthquakes are typically not felt by people and are only recorded by seismographs. In the United States, thousands of these tiny earthquakes occur each year. They’re so common that seismologists often don’t even report them to the public unless there’s a particular scientific interest.
Minor Earthquakes (Magnitude 2.5 to 5.4)
Earthquakes in this range can often be felt by people, especially those close to the epicenter, but they rarely cause damage. The United States experiences hundreds of these earthquakes annually. You might notice hanging objects swaying or hear rattling sounds during these events, but structural damage is uncommon.
Moderate Earthquakes (Magnitude 5.5 to 6.0)
These earthquakes can cause damage to poorly constructed buildings and other structures. The United States typically sees around 10 to 15 earthquakes in this magnitude range each year, though the number can vary. These events often make local news and may trigger emergency response protocols.
Strong to Major Earthquakes (Magnitude 6.1 and Above)
Fortunately, strong and major earthquakes are relatively rare in the United States. On average, the country experiences one to two earthquakes of magnitude 6.0 or greater per year. These powerful seismic events can cause significant damage and loss of life, particularly in populated areas with vulnerable infrastructure.
Where Do Most U.S. Earthquakes Occur?
When discussing earthquake frequency in the United States, location matters tremendously. Not all states experience earthquakes with the same frequency or intensity.
Alaska: The Earthquake Capital
Alaska takes the crown for the most seismically active state in the nation. The state experiences more earthquakes than all other U.S. states combined, averaging 40,000 per year. This high frequency is due to Alaska’s position along major tectonic plate boundaries, particularly where the Pacific Plate slides beneath the North American Plate.
Many of Alaska’s earthquakes occur in remote, unpopulated areas, which is why you might not hear about them frequently in the news. However, the state has experienced some of the most powerful earthquakes in U.S. history, including the 1964 Great Alaska Earthquake, which measured 9.2 on the moment magnitude scale.
California and the San Andreas Fault
California is probably the state most Americans associate with earthquakes, and for good reason. The state experiences thousands of earthquakes annually, though most are too small to feel. California’s position along the San Andreas Fault and other significant fault lines makes it particularly vulnerable to seismic activity.
On average, California experiences one or two earthquakes large enough to cause damage each year. The state’s combination of high seismic activity and dense population makes earthquake preparedness a critical public safety issue.
Other Active Regions
While Alaska and California dominate the earthquake statistics, other regions also experience notable seismic activity. Nevada, Hawaii, Washington, Wyoming, Idaho, and Montana all record significant numbers of earthquakes each year. The Cascadia Subduction Zone along the Pacific Northwest coast poses a particular long-term threat, with scientists warning that a major earthquake is overdue in this region.
Even states not traditionally associated with earthquakes have experienced seismic events. The central United States, including Oklahoma, Kansas, and Texas, has seen increased earthquake activity in recent years, largely attributed to human activities such as wastewater injection from oil and gas operations, often referred to as fracking.
Why Earthquake Frequency Varies
Several factors influence how often earthquakes occur in different regions and time periods.
Tectonic Plate Boundaries
The primary driver of earthquake frequency is the movement of Earth’s tectonic plates. Areas located along plate boundaries, where plates collide, separate, or slide past each other, experience far more earthquakes than stable continental interiors. This is why the western United States, positioned along the Pacific Ring of Fire, is so seismically active.
Induced Seismicity
Human activities can trigger earthquakes, a phenomenon known as induced seismicity. The injection of wastewater from oil and gas operations deep underground can increase pore pressure along existing faults, making them more likely to slip. This has led to a dramatic increase in earthquake frequency in some regions that were previously relatively quiet.
Other human activities that can induce earthquakes include reservoir impoundment behind large dams, geothermal energy extraction, and mining operations. While these induced earthquakes are typically small, they can occasionally reach magnitudes that cause concern.
Aftershocks and Earthquake Sequences
When a significant earthquake occurs, it’s often followed by numerous aftershocks. These smaller earthquakes happen as the crust adjusts to the changes caused by the main shock. Aftershock sequences can continue for days, weeks, or even months after a major earthquake, temporarily increasing the earthquake count in that region.
What This Means for Preparedness
Understanding earthquake frequency helps inform preparedness efforts. If you live in a seismically active region, the question isn’t if an earthquake will occur, but when.
Building Codes and Infrastructure
Areas with frequent earthquake activity have typically implemented strict building codes designed to help structures withstand seismic shaking. California, for instance, has some of the most stringent earthquake-resistant building requirements in the world. These codes are constantly updated based on lessons learned from past earthquakes and advances in engineering.
Early Warning Systems
The high frequency of earthquakes has led to the development of early warning systems. The ShakeAlert System, operating along the West Coast, can provide seconds to tens of seconds of warning before strong shaking arrives. While this might not sound like much time, it can be enough to drop, cover, and hold on, or for automated systems to shut down critical infrastructure. Be ShakeAlert® Safe
Personal Preparedness
Living in an earthquake-prone area requires personal preparedness. This includes securing heavy furniture and other objects that could fall during an earthquake, maintaining an emergency kit with food, water, and medical supplies, and having a family communication plan. Because earthquakes occur so frequently, even if most are small, it’s wise always to be prepared for a larger event.
How To Be Ready For The Next Earthquake
The Bottom Line on Earthquake Frequency
Earthquakes are a daily occurrence in the United States, with dozens happening every single day across the country. The vast majority are too small to feel, but the frequency serves as a constant reminder that we live on an active, dynamic planet.
While we can’t predict exactly when or where the next significant earthquake will strike, we can use our understanding of earthquake frequency and patterns to prepare ourselves and our communities better. Whether you live in earthquake country or are just visiting, knowing these earthquake tidbits helps you understand the seismic landscape of the United States and the importance of always being prepared.
Final Word
The key takeaway is this: earthquakes are far more common than most people realize, occurring thousands of times per year in the United States alone. By understanding this frequency and the factors that influence it, we can make informed decisions about where we live, how we build, and how we prepare for the inevitable next shake. May God bless this world, Linda
Copyright Images: Earthquake in Hawaii AdobeStock_256717295 By Louis-Paul Photo, Earthquake Tsunami Warning Newport Beach CA AdobeStock_286203554 By Felipe Sanchez, Earthquake and Tsunami Warning in Santa Cruz CA AdobeStock_234568734 By Sundry Photography
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