North America is a geologically active continent that experiences frequent seismic events, which include both minor tremors and large, destructive earthquakes. The distribution of this activity is not uniform, concentrating in specific regions where tectonic plates meet or where ancient weaknesses lie within the continental crust. Understanding where this shaking occurs most often requires examining the complex interactions between the continent’s major tectonic plates.
The Tectonic Drivers of North America
Nearly all seismic activity in North America results from the movement and interaction of massive tectonic plates. The continent primarily rides on the North American Plate, but its boundaries are defined by friction and collision with neighboring plates. The most significant boundary is along the western edge, where the North American Plate meets the Pacific Plate and the smaller Juan de Fuca Plate. This interaction involves two main types of movement: transform and subduction. Transform boundaries, like the San Andreas Fault system, involve plates sliding horizontally past each other, releasing strain in strike-slip earthquakes, while subduction zones occur where a denser oceanic plate dives beneath a continental plate, generating the potential for megathrust earthquakes.
The Most Active Region: Alaska and the Aleutian Arc
Alaska and its associated Aleutian Arc experience the highest frequency and magnitude of seismic events in North America. This region lies directly on the boundary where the dense Pacific Plate is actively subducting beneath the North American Plate. This convergence creates the Alaska-Aleutian subduction system, one of the most seismically active zones globally, producing more earthquakes of magnitude 8 or greater in the last century than any other region. The geological complexity generates earthquakes from multiple sources, including shallow crustal earthquakes from the deformation of the overriding North American Plate and interplate earthquakes at the boundary interface itself. The most powerful historical event in North America, the magnitude 9.2 Great Alaska Earthquake, occurred here in 1964.
High-Risk Zones of the Contiguous West Coast
South of Alaska, the contiguous western coast of the United States and Canada features highly active seismic zones characterized by different hazards. California’s seismic landscape is dominated by the San Andreas Fault system, which marks a major transform boundary between the Pacific and North American Plates. Along this fault, the plates grind past each other horizontally, leading to frequent strike-slip earthquakes, such as the destructive 1906 San Francisco event.
The Cascadia Subduction Zone
Further north, the Pacific Northwest is defined by the Cascadia Subduction Zone, stretching from Northern California to British Columbia. Here, the Juan de Fuca Plate is subducting beneath the North American Plate. This zone poses the threat of a megathrust earthquake, capable of reaching magnitude 9.0 or higher. Such an event last occurred in 1700, sending a tsunami all the way to Japan.
Significant Activity Away From Plate Boundaries
Seismic activity is not exclusive to the continent’s edges; significant earthquakes can also occur within the interior of the stable North American Plate, known as intraplate seismicity. The most notable of these interior zones is the New Madrid Seismic Zone (NMSZ), which stretches through parts of Missouri, Arkansas, Tennessee, and Kentucky. This zone is associated with the ancient Reelfoot Rift, a network of fractures that formed when the continent began to pull apart. The NMSZ was the source of a powerful sequence of earthquakes in 1811–1812, with the largest estimated between magnitude 7 and 8.
Earthquakes here pose a unique hazard because the continental crust in the central and eastern U.S. allows seismic energy to travel much farther, potentially damaging structures over a larger area. Human activity has also triggered a rise in induced seismicity in regions like Oklahoma and Texas, primarily due to the high-volume injection of wastewater deep underground.