Earthquakes have long been associated with fault lines, jagged edges where tectonic plates meet and collide. Several studies explain how these seismic activities are not limited to these boundaries.
According to the US Geological Survey, most earthquakes, approximately 90%, occur along the edges of tectonic plates, such as the infamous San Andreas Fault, which runs along the western coast of California.
Despite this, scientists have discovered examples of earthquakes occurring far from these fault lines, prompting a rethinking of our understanding of seismic events.
A notable case study that challenges conventional wisdom is the series of earthquakes that shook New Madrid, Missouri, in the early nineteenth century.
These earthquakes, which occurred thousands of miles from the nearest fault line and ranged in magnitude from 7.2 to 8.2, caused widespread devastation and long-term impact on the region.
Their occurrence raises an important question: how can earthquakes occur in areas that appear to be far from typical seismic hotspots?
How Earthquakes Happen Away From a Fault Line
Researchers have proposed several hypotheses to explain intraplate earthquakes (or mid-plate tectonic activity), which occur within the interior of tectonic plates. A particular theory suggests a link between ancient glaciers and seismic activity.
During the last ice age, massive ice sheets covered much of North America, putting tremendous pressure on the Earth's crust. As the glaciers melted, the land rebounded, which could cause earthquakes as the crust adjusted to the shifting weight distribution.
Another plausible explanation involves the reactivation of old faults within tectonic plates. Over eons, the Earth's crust has undergone extensive deformation, leaving dormant faults vulnerable to stress-induced fracture. When external forces act on these weakened zones, they may reactivate, resulting in seismic events.
Additionally, the composition of the Earth's crust and the presence of fluid-filled channels influence intraplate seismic activity. Hydraulic fracturing, also known as fracking, injects fluids into underground rocks to extract oil or natural gas.
This process may inadvertently lubricate old faults, raising the risk of earthquakes. Furthermore, the injection of wastewater from fracking operations into deep wells can exacerbate seismic activity.
NEW YORK, NEW YORK - APRIL 5: In this photo illustration, an emergency alert is displayed from the national Emergency Broadcast System warning of an earthquake in the area on April 5, 2024 in New York City. The earthquake was first reported as 4.7 magnitude but later upgraded to 4.8. There were no reported injuries in the late morning earthquake, but many people reported visible shaking in buildings and homes. Tremors were felt from Philadelphia to Boston. Photo Illustration by David Dee Delgado/Getty Images
How Scientists Track These Earthquakes
To better understand intraplate earthquakes, scientists are using advanced technologies and research initiatives such as EarthScope. These projects provide valuable insights into previously unknown seismic activity by deploying sensors to capture the dynamics beneath the Earth's surface.
For example, EarthScope's findings have challenged the notion that seismic events are limited to plate boundaries, shedding light on the complexities of the Earth's interior.
The implications of intraplate earthquakes go beyond scientific curiosity; they have real-world consequences for communities living in seismic zones.
