Earthquake Risk in the US
Which regions face the greatest seismic hazard, major fault systems, historical patterns, and what USGS data reveals about earthquake frequency.
Key Takeaway
Alaska is the most seismically active US state by far, followed by California. The Cascadia Subduction Zone poses the highest catastrophic risk — capable of an M9+ earthquake and Pacific Northwest tsunami. The central US New Madrid Seismic Zone and the eastern seaboard are also at risk, though less frequently active. Between 2013–2016, Oklahoma surged to become one of the most earthquake-prone states due to wastewater injection, demonstrating that human activity can significantly alter regional seismic risk.
The West Coast: Highest Ongoing Risk
The western United States sits along the Pacific Ring of Fire, where tectonic plates are actively colliding, grinding, and subducting. Three major fault systems define western seismicity:
- San Andreas Fault System (California): A 1,300-km right-lateral strike-slip fault running through most of California. The San Andreas and its many associated faults (Hayward, Calaveras, San Jacinto, Elsinore) produce thousands of earthquakes annually. The southern section — from Parkfield to the Salton Sea — is considered overdue for a major rupture. Scientists estimate an approximately 60% probability of an M6.7+ earthquake in the San Francisco Bay Area within the next 30 years.
- Cascadia Subduction Zone (Pacific Northwest): The Juan de Fuca Plate is actively diving beneath North America along this offshore megafault. Unlike the San Andreas, which produces frequent moderate earthquakes, the Cascadia zone "locks" for centuries and then releases enormous energy in megathrust events. The last full-margin rupture was January 26, 1700 — known from Japanese tsunami records and Pacific Northwest coastal geology.
- Alaska Aleutian Arc: Alaska sits at the convergence of the Pacific and North American plates and experiences more large earthquakes than any other US state. The 1964 Good Friday earthquake (M9.2) remains the second-largest ever instrumentally recorded.
The Intermountain West
The Basin and Range Province — encompassing Nevada, Utah, western Arizona, and parts of Idaho — is one of the most seismically active regions in the US outside of California and Alaska. The region is actively stretching, creating a series of normal faults (where one side drops relative to the other). The Wasatch Front in Utah, running through Salt Lake City, is considered capable of producing an M7+ earthquake. Nevada records more M4+ earthquakes per square mile than California in some years.
Washington and Oregon, beyond the Cascadia offshore threat, also have active crustal faults capable of M6–7 events. The 2001 Nisqually earthquake (M6.8) near Olympia, Washington caused over $2 billion in damage and is a reminder that shallow crustal earthquakes remain a serious hazard in the Pacific Northwest independent of the megathrust scenario.
Central US: New Madrid and Induced Seismicity
The New Madrid Seismic Zone (NMSZ) cuts through the central Mississippi Valley — Missouri, Arkansas, Tennessee, Kentucky, and Illinois. The 1811–1812 New Madrid earthquakes were among the largest in US history, estimated at M7.5–8.0+. Ground effects included sand blows (liquefaction features), river bank collapses, and temporary reversal of the Mississippi River's flow in some locations. These events were so powerful they rang church bells in Boston and were felt across much of the eastern US.
More recently, the central US experienced a dramatic surge in seismicity from induced earthquakes. Oklahoma averaged fewer than 2 M3+ earthquakes per year before 2009. By 2015, it averaged over 900 per year — briefly making it the most seismically active state in the contiguous US. The cause: mass disposal of oil and gas extraction wastewater into deep injection wells, increasing pore pressure along dormant faults. After regulators reduced injection volumes, Oklahoma's earthquake rate fell substantially.
Browse US state earthquake data to see how each state's seismic activity has changed over the 2005–2025 USGS record.
Eastern US: Lower Frequency, Wide Impact
The eastern United States is geologically old and stable — ancient Precambrian rock that doesn't produce frequent earthquakes. But when earthquakes do occur, the dense, cold rock transmits seismic waves far more efficiently than the fractured western rock. The 2011 Virginia earthquake (M5.8) was felt by an estimated 1/3 of the US population — far more than a similar-magnitude California earthquake would affect. Eastern building stock, largely designed without seismic codes, adds to the vulnerability.
Key eastern seismic zones include the Wabash Valley (Illinois/Indiana border), the Charlevoix Seismic Zone (Quebec), and various historical fault zones in New England. Charleston, South Carolina experienced an M7.3 earthquake in 1886 that killed at least 100 people. The USGS National Seismic Hazard Model incorporates these zones into its assessment of eastern US risk.
Regional Hazard Comparison Table
The USGS National Seismic Hazard Map 2023 quantifies the regional differences described above as Peak Ground Acceleration (PGA) values mapped to FEMA Seismic Design Categories used in the International Building Code:
| Region | Representative metro | PGA design value | FEMA SDC |
|---|---|---|---|
| Coastal California | Los Angeles, San Francisco | 0.50-0.75g | E |
| Pacific Northwest | Portland, Seattle | 0.30-0.45g | D |
| Wasatch Front | Salt Lake City | 0.30-0.40g | D |
| New Madrid SZ | Memphis, St. Louis | 0.18-0.25g | D |
| Charleston SZ | Charleston SC | 0.20-0.28g | D |
| Central US (background) | Indianapolis, Chicago | 0.06-0.12g | C |
| Eastern US (low) | New York, Boston | 0.04-0.10g | B-C |
Why coastal California ranks SDC E
The San Andreas plate boundary slips at roughly 35 mm/yr through the Bay Area and southern California. Combined with intermediate thrust faults (Transverse Ranges) and basin enhancement (Los Angeles, Santa Clara Valley), design PGA frequently exceeds 0.50g — placing nearly every major coastal-California metro in SDC E for new construction. The 2008 USGS-FEMA HayWired scenario projected $112B direct loss from a Mw 7.0 Hayward Fault rupture and 800 fatalities.
Why the Pacific Northwest is reclassified upward
USGS NSHM 2023 increased Cascadia subduction-zone hazard estimates after new paleoseismic trenching at Willapa Bay and Discovery Bay confirmed at least seven Mw 8.7+ ruptures in the past 3,500 years. The mean recurrence interval is now estimated at 250 years; the most recent full-margin event was January 26, 1700. This drives Portland and Seattle metro design values from earlier 0.20g into the 0.30-0.45g range.
Worked example: a hospital relocation tradeoff
A 200-bed regional hospital developer compares two sites. Site A in Salt Lake City sits at PGA 0.35g (SDC D) on Class C soil — Risk Category IV requires special concentrically braced frames and base isolation, adding $4.5M to the structural budget vs an SDC C baseline at $2.1M. Site B in Indianapolis sits at PGA 0.08g (SDC C) on Class D soil — basic intermediate moment frame at $1.8M structural cost. Annual earthquake-property insurance premiums: Site A averages 38% loaded vs Site B's 8% loaded for the same coverage limit. Lifecycle cost-of-resilience ratio: roughly 4.2x higher in Salt Lake. Decision often comes down to whether trauma-center catchment and Medicare patient volume (3.2x higher in SLC for the modeled service area) justify the seismic premium.
When central-US moderate-hazard becomes high-risk
The New Madrid Seismic Zone delivers a sobering complication: 75% of buildings in the Memphis metro predate the 1996 IBC adoption, and 25% of those are unreinforced masonry — the most fragile typology under any ground motion above 0.10g. A repeat of the 1811-1812 sequence (estimated Mw 7.3-7.5) in modern St. Louis or Memphis has been modeled by FEMA HAZUS at $300B+ direct loss with 4,500 fatalities, despite only moderate-hazard PGA design values. This is the textbook case for vulnerability dominating the risk equation.
What USGS Data Reveals
The 20-year PlainQuake dataset (2005–2025) provides a clear picture of US seismic frequency. Alaska dominates in both event count and maximum magnitudes. California shows consistent high-frequency activity across its complex fault system. The central US spike from 2013–2016 is visible in state-level data, particularly Oklahoma, Kansas, and Texas.
The USGS National Seismic Hazard Model — updated regularly — estimates that about 42 of the 50 US states have a reasonable chance of experiencing damaging ground motion in the next 50 years. Explore state-level statistics and year-by-year trends to see how seismic activity has evolved over the 20-year USGS record.
Safety Note
During an earthquake, Drop, Cover, and Hold On. Drop to your hands and knees, take cover under a sturdy table or desk, and hold on until shaking stops. If you are in a high-risk area, create a preparedness kit and family communication plan before an earthquake occurs.
Frequently Asked Questions
Which US state has the most earthquakes?
Alaska has by far the most earthquakes of any US state — it experiences more M7+ earthquakes than anywhere else in the world, recording more seismic activity than the contiguous 48 states combined. The 2002 Denali Fault earthquake (M7.9) and the 1964 Good Friday earthquake (M9.2, the second-largest ever recorded) both occurred in Alaska. California ranks second in total earthquake count among the lower 48, with Oklahoma recently surging to high activity levels due to induced seismicity from wastewater injection.
What is the Cascadia Subduction Zone and how dangerous is it?
The Cascadia Subduction Zone is a 1,000-km fault system running offshore from northern California through Oregon and Washington to British Columbia, Canada. It is capable of producing megathrust earthquakes of M8–M9+, similar to the 2011 Tohoku earthquake in Japan. Geologic evidence shows Cascadia has produced full-margin ruptures approximately every 200–500 years, with the last one in January 1700. Scientists estimate a roughly 10–15% probability of a full Cascadia rupture in the next 50 years. Such an event would generate a major Pacific Northwest tsunami within 15–20 minutes.
How did Oklahoma become one of the most seismically active states?
Oklahoma went from averaging fewer than 2 M3+ earthquakes per year before 2009 to over 900 per year by 2015. The cause is induced seismicity — not fracking itself, but the injection of enormous volumes of wastewater (a byproduct of oil and gas production) into deep disposal wells. This fluid injection increases pore pressure along pre-existing faults, reducing the friction that keeps them locked. After regulatory actions reduced injection volumes, Oklahoma's earthquake rate declined significantly, confirming the link. The USGS has published extensive induced seismicity research on this phenomenon.
Is the New Madrid Seismic Zone still a threat?
Yes. The New Madrid Seismic Zone (NMSZ) in the central US — spanning parts of Missouri, Arkansas, Tennessee, Kentucky, and Illinois — produced a sequence of massive earthquakes in 1811–1812, including three events estimated at M7.5–M8.0. These caused ground liquefaction, river reversals, and were felt across the eastern US. The NMSZ remains active with frequent small earthquakes. A repeat of the 1811–1812 sequence today would be catastrophic because Midwestern building stock is largely not earthquake-resistant, unlike California construction.
Do earthquakes happen on the East Coast?
Yes, though less frequently than in the West. The 2011 Virginia earthquake (M5.8) near Mineral, VA was felt by more people than any other US earthquake in history due to the efficiency of eastern rock at transmitting seismic waves — the same magnitude earthquake shakes a much larger area in the east than in the seismically fractured west. Charleston, South Carolina experienced a destructive M7.3 earthquake in 1886. The Wabash Valley Seismic Zone in Illinois/Indiana is also considered moderately active.
What does USGS data reveal about earthquake frequency trends?
USGS ComCat data from 2005–2025 shows that global M4+ earthquake frequency has been relatively stable, averaging around 15,000–16,000 events per year. Major event counts fluctuate: years with large subduction zone earthquakes (like 2011 with the M9.1 Tohoku event) see elevated aftershock sequences that inflate annual totals. In the US, induced seismicity caused a clear spike in the 2013–2016 period, particularly in Oklahoma, Texas, and Kansas. Browse PlainQuake yearly statistics for year-by-year breakdowns.
Sources
- USGS Earthquake Hazards Program — ComCat Catalog, 2005–2025
- USGS — National Seismic Hazard Model (NSHM)
- USGS — Induced Seismicity Research
- USGS — New Madrid Seismic Zone
- USGS — Cascadia Subduction Zone
This content is for educational purposes only. For official seismic hazard assessments, emergency preparedness information, and real-time earthquake data, visit earthquake.usgs.gov and ready.gov.
Understanding the Data
The information presented throughout this guide is informed by publicly available public records published by federal and state government agencies. Our database aggregates and standardizes these records to make them more accessible and easier to interpret for general audiences. When we reference specific statistics or trends, they are drawn directly from these authoritative sources unless explicitly noted otherwise.
It is important to understand the limitations of any large-scale data dataset. Records may contain errors from the original data collection process, some fields may be incomplete for older entries, and classification systems may have changed over time. Our analysis accounts for these factors by clearly labeling data vintage, flagging records with missing critical fields, and noting when temporal comparisons span methodology changes in the source data.
For readers who want to conduct their own research, we recommend going directly to the source whenever possible. federal and state government agencies provides detailed documentation on collection methodology, sampling frames, and known data quality issues. Our goal is not to replace primary sources but to make them more approachable and to highlight patterns that may not be immediately obvious when browsing raw records.
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