How do earthquakes happen?
- According to the theory of plate tectonics, the Earth’s crust and upper mantle are made of large rigid plates that can move relative to one another. Slip on faults near the plate boundaries can result in earthquakes.
- The point inside the Earth where the earthquake rupture starts is called the focus or hypocentre. The point directly above it on the surface of the Earth is the epicentre.
What are seismic waves?
- Any elastic material when subjected to stress, stretches in a proportional way, until the elastic limit is reached. When the elastic limit is crossed, it breaks.
- Similarly, the Earth also has an elastic limit and when the stress is higher than this limit, it breaks. Then there is a generation of heat, and energy is released. Since the material is elastic, the energy is released in the form of elastic waves.
- These propagate to a distance determined by the extent of the impact. These are known as seismic waves.
