Seismic Hazards

Earthquakes are the most widespread tectonic hazard, affecting every continent. They are responsible for more deaths than any other geological hazard: between 2000 and 2020, earthquakes and associated tsunamis killed over 780,000 people worldwide (USGS). Understanding the physical processes that generate earthquakes, the scales used to measure them, the phenomenon of tsunamis, and the factors that determine their impact is essential for A-Level Geography.

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What Causes Earthquakes?

Key Definition: An earthquake is a sudden release of stored elastic energy in the Earth's lithosphere, causing seismic waves to radiate outward from the point of energy release.

Elastic Rebound Theory

The elastic rebound theory was formulated by Harry Fielding Reid (1910) following his study of the 1906 San Francisco earthquake. The theory states:

1. Tectonic stress causes rocks on either side of a fault to deform elastically (like stretching a rubber band)
2. Friction along the fault plane locks the rocks in place, preventing movement
3. When the accumulated stress exceeds the frictional strength of the fault, the rocks suddenly snap back to their undeformed shape
4. This sudden displacement releases energy as seismic waves