The New Madrid Seismic Zone is the most seismically active area in the United States east of the Rocky Mountains — and a profound anomaly: a major earthquake hazard in the middle of a continent, far from any plate boundary. It produced the largest earthquakes in US recorded history outside the West, the 1811–1812 sequence. Unlike the San Andreas, its faults are buried deep beneath the sediment of the Mississippi embayment and have almost no expression at the surface — which is why this zone does not appear as a bold line on fault maps.
The USGS models the New Madrid seismic zone as a fault source, with earthquakes of M6.6–8.0 across 23 alternative fault traces — the model is uncertain exactly where the buried faults run, so it weighs several.
Source: USGS NSHM23 fault sections database v3 and western US geologic deformation model v1.0 (on-plane slip rates, preferred with low–high range; site data = measured sites in the NSHM23 earthquake-geology database, rate class only = the fault’s mapped slip-rate category); central US and Cascadia sources from the model’s source files (code.usgs.gov/ghsc/nshmp/nshms/nshm-conus).
Between December 1811 and February 1812, three great earthquakes struck the region: December 16, 1811 (M~7.5, northeast Arkansas), January 23, 1812 (M~7.3, Missouri), and February 7, 1812 (M~7.5, on the Reelfoot fault in Missouri/Tennessee, which formed Reelfoot Lake). All magnitudes are reconstructions from historical felt reports — no instruments existed — and estimates genuinely range from about M7.0–7.5 (Hough et al.) to ~M8.1 (Johnston 1996); USGS's current summaries settle near M7.5/7.3/7.5. Damaging strong shaking covered roughly 600,000 km², and the quakes were felt over ~2.5 million km² — chimneys were damaged as far away as Cincinnati and St. Louis.
The faults here are not visible at the surface: they are eroded by river processes and deeply buried by river sediment. They are known from geophysics (seismic reflection profiles), the pattern of modern seismicity, and paleoseismic evidence such as sand blows — not from continuous surface rupture. Even the USGS Quaternary Fault Database entry (#1023) describes the Reelfoot Scarp as "a fold scarp, not a fault surface trace," with the underlying thrust fault identified only in seismic reflection profiles, slip rate "unknown," and no trench investigations. The structures sit over the Reelfoot Rift, an ancient failed continental rift now reactivated under compression.
How fast the zone is loading — and how often it ruptures — is actively contested. Geologic work (Mueller et al., 1999, Science) found right-lateral slip of 1.8–2.0 mm/yr, while GPS studies (Calais & Stein; Craig & Calais 2014) measure no detectable deformation (upper bound ~0.2 mm/yr). Recurrence estimates range from ~500-year clusters (paleoseismology: three or more M7+ events in the last 2,000 years) to as long as ~2,500 years under GPS-based assumptions. USGS maintains the hazard assessment on the strength of the geologic and historical record despite the low GPS rates.
Cold, rigid continental crust transmits seismic energy far more efficiently than the fractured crust of the West — so a New Madrid earthquake shakes a vastly larger area than a same-magnitude California quake. The 1811–1812 shaking was felt over ~2.5 million km². USGS estimates a 25–40% chance of M6.0+ and a 7–10% chance of a repeat of the 1811–1812 sequence in the next 50 years. At risk: Memphis, St. Louis, Little Rock, and communities across the central Mississippi River Valley.
The New Madrid zone is the reason the central United States — not just the West — must prepare for major earthquakes. See the state pages along the zone and our seismic risk lookup.