US Earthquake Risk — Overview
The United States experiences thousands of earthquakes every year. Here's what you need to know about seismic risk, magnitude, and which regions are most vulnerable.
Earthquake Magnitude: Richter vs. Moment Magnitude
Most people have heard of the Richter scale, developed in 1935 by Charles Richter for measuring California earthquakes. Today, seismologists use the Moment Magnitude scale (Mw), which is more accurate for large earthquakes and is what USGS reports. Both scales are logarithmic — each whole number increase represents approximately 31.6 times more energy released.
How to Interpret Earthquake Magnitude
| Magnitude | Classification | Effects | Frequency (worldwide) |
|---|---|---|---|
| M8.0+ | Great | Devastating damage; felt 1,000+ miles away | ~1 per year |
| M7.0–7.9 | Major | Serious damage in populated areas | ~18 per year |
| M6.0–6.9 | Strong | Moderate damage, felt widely | ~120 per year |
| M5.0–5.9 | Moderate | Slight structural damage to buildings | ~800 per year |
| M4.0–4.9 | Light | Felt by many; minor damage | ~6,200 per year |
| M3.0–3.9 | Minor | Often felt; rarely causes damage | ~49,000 per year |
Which US States Are Most At Risk?
Alaska experiences more earthquakes than any other state — seven of the ten largest earthquakes in US history occurred there. In the contiguous 48 states, California, Oregon, and Washington face the highest seismic risk from the Pacific plate boundary (San Andreas Fault, Cascadia Subduction Zone).
The New Madrid Seismic Zone in the central Mississippi Valley (Missouri, Arkansas, Tennessee, Illinois) is also high-risk — the 1811–1812 New Madrid earthquakes (estimated M7.5–8.0) are among the largest in North American history.
The Pacific Northwest Megaquake represents one of the most significant long-term risks: the Cascadia Subduction Zone could produce an M8.7–9.2 earthquake affecting Oregon, Washington, and northern California.
What to Do Before, During, and After an Earthquake
Before: Secure heavy furniture, water heaters, and appliances. Have an emergency kit with 72 hours of supplies. Know your building type — wood-frame buildings generally perform better than unreinforced masonry.
During: Drop, Cover, and Hold On. Get under a sturdy table or against an interior wall away from windows. Do not run outside.
After: Check for gas leaks (leave if detected, don't use flames/switches). Be prepared for aftershocks. Listen to official emergency broadcasts.