The Role of Tectonic Plates
Earthquakes are primarily caused by the sudden release of energy that has accumulated over time due to the movement of large sections of Earth's lithosphere, known as tectonic plates. These massive plates are constantly, albeit slowly, moving, driven by convection currents in the planet's mantle. When the stress from this movement exceeds the strength of the rocks along their boundaries, a sudden slip occurs.
Stress Accumulation and Fault Rupture
The edges of tectonic plates are not smooth; they are jagged and often get 'stuck' due to friction. As plates continue to move, stress builds up in the rocks along these locked boundaries, known as fault lines. This accumulated stress deforms the rocks. When the stress becomes too great to be resisted by friction, the rocks snap, and the plates abruptly slide past each other, releasing the stored energy in the form of seismic waves.
Types of Plate Boundaries and Faults
Earthquakes occur most frequently at plate boundaries: transform boundaries where plates slide horizontally past each other (e.g., San Andreas Fault), convergent boundaries where plates collide (one often subducts beneath the other, causing deep and powerful quakes), and divergent boundaries where plates pull apart (leading to shallower, less intense quakes). The type of fault (strike-slip, normal, reverse) corresponds to the direction of relative movement between the rock blocks.
Consequences and Global Impact
The energy released during an earthquake travels through the Earth as seismic waves, causing the ground to shake. This shaking can lead to structural damage, liquefaction, landslides, and tsunamis if the earthquake occurs under the ocean. Understanding the causes of earthquakes is crucial for seismic hazard assessment, informing building codes, and developing early warning systems to mitigate their devastating impact on human populations and infrastructure.
Understanding Aftershocks
After an initial earthquake (the mainshock), smaller earthquakes known as aftershocks often follow. These are caused by the readjustment of rocks along the fault line or nearby faults in response to the main rupture. Aftershocks can continue for days, weeks, or even months, gradually decreasing in magnitude and frequency over time.