The United States has fault lines in every region, not just California. The most seismically active zones run along the Pacific Coast, through Alaska’s Aleutian Islands, and across a surprisingly dangerous stretch of the central Midwest. But buried faults also thread through the Northeast, the Southeast, and the Intermountain West, creating earthquake risk in places most people don’t expect.
The USGS updated its 50-State National Seismic Hazard Model in 2023, and the picture it paints is broader than the San Andreas alone. Here’s where the major fault systems are and what they mean for the people living near them.
California’s San Andreas and Related Faults
The San Andreas Fault is the most famous fault line in the country, running roughly 800 miles from the Salton Sea in Southern California to Cape Mendocino in the north. It marks the boundary where the Pacific Plate slides northwest past the North American Plate. But the San Andreas isn’t a single clean line. It’s part of a broader system that includes the Hayward Fault running through the East Bay near Oakland and Berkeley, the San Jacinto Fault in Southern California, and dozens of smaller faults branching off in every direction.
The San Andreas produced the devastating 1906 San Francisco earthquake (estimated magnitude 7.9) and the 1857 Fort Tejon earthquake in Southern California (magnitude 7.9). Both the northern and southern segments of the fault are considered overdue for a major rupture based on their historical patterns.
The Cascadia Subduction Zone
Stretching over 1,100 kilometers from Northern California to British Columbia, the Cascadia Subduction Zone is where the Juan de Fuca Plate dives beneath the North American Plate along the Pacific Northwest coast. This fault is capable of producing a magnitude 9.0 earthquake, comparable to the 2011 event that devastated Japan. Scientists estimate the probability of such an event occurring in the coming decades at 10% to 14%.
The last full rupture of the Cascadia zone happened on January 26, 1700, generating a massive tsunami that reached Japan. The roughly 300-year gap since then, combined with geological evidence of repeated past ruptures, is what drives the concern. Washington, Oregon, and far Northern California sit directly in the impact zone.
The Seattle Fault Zone
Separate from the Cascadia Subduction Zone, the Seattle Fault Zone runs east to west through the middle of Seattle itself. This is a shallow crustal fault capable of producing a magnitude 7.0 earthquake with consequences that would be severe for a dense urban area. About 15% of Seattle’s total land area sits on soil prone to ground failure during strong shaking, with the Duwamish Valley, Interbay, and Rainier Valley especially vulnerable to liquefaction.
A large Seattle Fault earthquake could trigger a tsunami up to 16 feet high in Puget Sound, striking the city’s shoreline within seconds and flooding low-lying areas within five minutes. The city’s many bridges, despite seismic retrofits, may not be usable afterward, cutting off emergency response routes. Dozens of fires could break out simultaneously, with damaged water infrastructure reducing the pressure needed to fight them.
Alaska’s Aleutian Megathrust
Alaska is by far the most seismically active state. The Aleutian megathrust, where the Pacific Plate is being forced beneath the North American Plate, is one of the most active seismic zones on Earth. The region averages two magnitude 6.0 or greater earthquakes per year. Alaska produced the largest earthquake ever recorded in North America: the 1964 Great Alaska Earthquake at magnitude 9.2.
The fault system arcs along the Aleutian Islands and curves into the Gulf of Alaska, putting coastal communities at risk from both ground shaking and tsunamis. Because most of the zone is remote, the direct threat to large populations is lower than in the Pacific Northwest, but the tsunamis it generates can travel across the entire Pacific basin.
The New Madrid Seismic Zone
The most dangerous fault system east of the Rockies lies in the middle of the continent. The New Madrid Seismic Zone runs through northeastern Arkansas, southeastern Missouri, southwestern Kentucky, and northwestern Tennessee. In the winter of 1811 and 1812, this zone produced a sequence of three massive earthquakes estimated between magnitude 7.0 and 8.0 that lasted for months, ringing church bells as far away as Boston and temporarily reversing the flow of the Mississippi River.
Paleoseismic studies have uncovered evidence that comparable earthquake sequences struck around 900 A.D. and 1450 A.D., plus earlier events around 300 A.D. and 2350 B.C. That pattern points to a recurrence interval of roughly 500 years for magnitude 7 to 8 earthquakes. The region hasn’t experienced anything close to that size since 1812, but the faults remain active. Cities like Memphis, St. Louis, and Little Rock sit within the broader impact zone, and the soft river sediments in the Mississippi Valley amplify shaking over long distances.
The Wasatch Fault in Utah
Running along the western base of the Wasatch Mountains, the Wasatch Fault passes directly through Utah’s most populated corridor, including Salt Lake City, Provo, and Ogden. The fault is divided into 10 segments, with the central portion between Brigham City and Nephi considered the most hazardous. On average, a significant earthquake occurs somewhere along this central stretch about every 350 years, and a damaging quake hits somewhere in the broader Wasatch Front region roughly every 120 years.
The Wasatch Fault isn’t the only active fault in Utah. The Hurricane Fault in southern Utah and the Needles Fault Zone in Canyonlands National Park are also considered among the state’s most active. But the Wasatch Fault gets the most attention because over 80% of Utah’s population lives along it.
The Ramapo Fault in the Northeast
The East Coast is far less seismically active than the West, but it isn’t fault-free. The Ramapo Border Fault system extends about 185 miles from southern New York through New Jersey and into Pennsylvania. It regularly produces small earthquakes, generally magnitude 3.0 or less, but it’s capable of larger events. In April 2024, a magnitude 4.8 earthquake struck on the Flemington Fault, part of the Ramapo system, making it the largest earthquake on the fault since a 1938 event near Trenton. Multiple aftershocks followed, including one of magnitude 4.0.
What makes East Coast earthquakes especially notable is that seismic waves travel much farther through the older, colder, more rigid rock of the eastern United States. A magnitude 4.8 quake in New Jersey was felt across multiple states, while a similar-sized event in California might barely be noticed a few towns over.
Charleston, South Carolina
The Southeast has its own hidden seismic threat. In 1886, a devastating earthquake struck Charleston, South Carolina, killing over 60 people and damaging most of the city’s buildings. The faults responsible are buried beneath thick layers of coastal sediment, making them invisible at the surface. USGS research has identified several of these structures: the Ashley River fault, the Summerville fault, and a more recently discovered feature called the Berkeley fault, all intersecting with a larger buried system called the East Coast Fault System.
These are ancient faults, dating to the Paleozoic era, that have been reactivated over hundreds of millions of years. The soft coastal plain sediments in the region amplify shaking, which is part of why the 1886 earthquake was so destructive. Low-level seismicity continues near Summerville, just northwest of Charleston, confirming the faults are still active.
Oklahoma’s Reactivated Faults
Oklahoma became one of the most seismically active states in the country starting in 2009, and from 2014 through 2017, its rate of magnitude 3.0 and larger earthquakes actually exceeded California’s. The cause wasn’t natural tectonic stress but industrial wastewater disposal. When large volumes of produced water from oil and gas operations are injected deep underground, the fluid pressure can reach ancient faults and reduce the friction holding them in place, triggering earthquakes.
The largest documented injection-induced earthquake was a magnitude 5.8 event in central Oklahoma in September 2016. Four magnitude 5.0 or greater earthquakes have struck the state, three of them in 2016 alone. The USGS has identified 17 areas across the central and eastern United States with elevated rates of induced seismicity. While regulatory changes have reduced Oklahoma’s earthquake rate from its peak, the underlying faults remain sensitive to pressure changes.
Hawaii’s Volcanic Faults
Hawaii’s fault systems are tied to volcanic activity rather than plate boundaries in the traditional sense. The islands sit over a volcanic hotspot, and the massive weight of the shield volcanoes creates large fault systems on their flanks. The Hilina Fault System on Kilauea’s south flank is the most concerning, capable of producing large earthquakes and potentially triggering landslides into the Pacific. A magnitude 7.7 earthquake struck this system in 1975, generating a local tsunami. The ongoing eruption cycles at Kilauea keep these faults under constant stress.
Reading the National Hazard Map
The 2023 USGS National Seismic Hazard Model maps the chance of damaging shaking (intensity strong enough to knock items off shelves and crack walls) within a 100-year window across all 50 states. The highest risk areas form a clear pattern: the Pacific Coast from Southern California through Alaska, the Cascadia zone, the Wasatch Front, the New Madrid zone, Charleston, and parts of the Northeast. The 2023 update also accounts for how soft soils in the Gulf and Atlantic coastal plains amplify seismic waves, raising the effective risk for communities built on those sediments even when the nearest fault is relatively distant.
The practical takeaway is that earthquake risk in the United States is not confined to California. Millions of people live near active faults in the Midwest, the Pacific Northwest, Utah, and along the East Coast. Many of these regions have less stringent building codes than California, meaning comparable earthquakes could cause disproportionate damage.