Formation of Earthquakes
Earthquakes form primarily due to the movement of tectonic plates that make up Earth's lithosphere. These plates float on the semi-fluid asthenosphere and interact at boundaries where they converge, diverge, or slide past each other. Stress builds up along faults—fractures in the crust—when plates are locked together. When the stress exceeds the strength of the rock, it suddenly releases energy in the form of seismic waves, causing the ground to shake.
Key Principles of Seismic Activity
The elastic rebound theory explains this process: rocks deform elastically under stress and then snap back to their original shape, releasing stored energy. Earthquakes can also result from volcanic activity or human-induced causes like mining or reservoir filling, but tectonic movements account for most. Seismic waves travel from the hypocenter (focus) to the epicenter on the surface, varying in type—P-waves (compressional), S-waves (shear), and surface waves (rolling)—each contributing to shaking intensity.
Practical Example: The 2011 Tohoku Earthquake
The 2011 Tohoku earthquake in Japan, magnitude 9.0, occurred due to the subduction of the Pacific Plate beneath the North American Plate along the Japan Trench. Built-up stress released, generating massive seismic waves that shook the region for over six minutes. This led to a devastating tsunami when the seafloor uplift displaced ocean water, highlighting how initial ground motion can trigger secondary hazards like waves up to 40 meters high that inundated coastal areas.
Mechanisms of Damage and Real-World Applications
Earthquakes cause damage through intense ground shaking that collapses buildings, liquefaction where saturated soil behaves like liquid, landslides on slopes, and tsunamis from undersea quakes. Surface rupture along faults can destroy infrastructure directly. Understanding these processes is crucial for seismic zoning, building codes with earthquake-resistant designs, and early warning systems, which allow seconds to minutes of preparation to mitigate loss of life and property in vulnerable regions.