Earthquakes are defined as the sudden shaking of the ground caused by the release of energy in the Earth’s lithosphere. Many people perceive that these events are occurring with greater frequency, raising the question of whether the planet is entering a more seismically active period. Understanding this perception requires distinguishing between the planet’s actual geological activity and the factors that amplify our awareness of it. The primary causes of earthquakes remain the same, but human activity and modern technology have altered both the localized risk and the speed with which we learn about distant events.
Examining the Data: Is Seismic Activity Truly Increasing
Analysis of long-term global seismic data suggests that the frequency of major earthquakes has remained relatively stable over the past century. The United States Geological Survey (USGS) reports that the annual average includes about 15 earthquakes in the magnitude 7 range and one earthquake of magnitude 8.0 or greater. While the number of these large events can fluctuate yearly due to natural clustering, the long-term trend shows no statistically significant increase in major seismicity.
The perception of an increase often stems from the dramatic rise in the number of recorded smaller earthquakes, particularly those below magnitude 5. This surge is a reflection of technological advancements, not a change in Earth’s processes. Since the 1970s, the global network of highly sensitive seismometers has expanded significantly, allowing scientists to detect thousands of events that would have been missed decades ago. This improved monitoring capability creates the illusion that the planet is shaking more often than it did historically.
The Primary Mechanism: Why Earthquakes Happen Naturally
The vast majority of natural earthquakes are a direct consequence of plate tectonics, the process where the Earth’s rigid outer layer, the lithosphere, is broken into large, slowly moving plates. These plates are constantly interacting at their boundaries—convergent, divergent, and transform—which generates immense stress in the crust. When plates lock up against one another, the continuous motion of the plate system forces the rocks near the boundary to bend and deform, accumulating strain energy over decades or centuries.
Elastic Rebound Theory
This process is explained by the elastic rebound theory, which posits that rocks behave like a stretched rubber band. The stored energy causes the rock along a fault line to deform slowly until the internal friction holding the fault together is finally overcome. When the rock’s strength is exceeded, the fault ruptures suddenly, and the two sides slip past each other, releasing the accumulated strain energy in the form of seismic waves. The rocks then snap back toward their original, undeformed shape, and the cycle of stress accumulation begins again.
Boundary Types
At convergent boundaries, where plates collide, one plate often subducts beneath the other, leading to the world’s deepest and most powerful earthquakes, such as those that occur around the Pacific Ring of Fire. Transform boundaries, like the San Andreas Fault, involve plates sliding horizontally past each other, generating shear stress and shallow, damaging strike-slip earthquakes. Even at divergent boundaries, where plates move apart, the extensional stress can cause normal faults to slip.
Human Influence: Induced Seismicity
While most earthquakes are tectonic, a localized increase in seismicity in certain regions has been directly linked to human industrial activities, a phenomenon known as induced seismicity. The most prominent cause of this localized increase, particularly in the central United States, is the deep injection of large volumes of wastewater from oil and gas operations into disposal wells. This wastewater increases the fluid pressure deep underground, which acts as a lubricant on pre-existing, stressed faults.
It is important to distinguish this from hydraulic fracturing, or “fracking,” which involves injecting fluid for a short period to crack rock and release resources. While hydraulic fracturing has caused some small, localized earthquakes, the long-term, high-volume disposal of wastewater is the primary driver of the significant rise in felt earthquakes in non-tectonic regions like Oklahoma.
Additionally, the impoundment of water behind large dams can also trigger earthquakes, known as reservoir-triggered seismicity. The weight of the reservoir and the increased water pressure permeating the ground can prematurely release tectonic strain on faults that were already near their breaking point. Induced earthquakes are generally smaller than the planet’s largest natural tectonic events. The key mechanism remains the same: human activity alters the subsurface stress and fluid pressure on faults already under tectonic strain, accelerating the release of energy.
Factors Amplifying Public Awareness
The perception that earthquakes are happening more frequently is also a function of modern communication and population density. The advent of instantaneous media and social networking means that a magnitude 5.0 earthquake occurring in a remote part of the world is reported globally within minutes. This constant stream of information makes distant seismic events feel more immediate and numerous than they did when news traveled much slower.
The global population has grown significantly, and more people are living in seismically active regions than ever before. This increased density means that a historical average earthquake count will now impact more communities and generate more news coverage. The combination of more people in harm’s way and a global news infrastructure that instantly transmits details of every felt tremor contributes substantially to the public’s impression of heightened seismic activity.