What is an earthquake?
Fault - A fracture in the rocks that make up the Earth’s crust.
Epicenter - The point at the surface of the Earth above the focus.
Plates - Massive rocks that make up the outer layer of the Earth’s surface and whose movement along faults triggers earthquakes.
Seismic waves - Waves that transmit the energy released by an earthquake.
Focus (Hypocenter) - The point within the Earth where an earthquake rupture starts.
Earthquakes
Earthquakes are caused by a sudden release of stress along faults in the earth's crust.
The Earth’s crust consists of 7 large lithospheric plates and numerous smaller plates (tectonic plates) that move
Towards each other (a convergent boundary)
Apart (a divergent boundary) or
Past each other (a transform boundary)
The continuous motion of tectonic plates causes a steady build-up of pressure in the rock strata on both sides of a fault.
It gets released as waves of seismic energy and propagate through the ground and over its surface and causes shaking as earthquakes.
P waves or primary waves – They are the first waves to be detected.
These are compressional waves that push and pull as they move through rock and fluids.
S waves or secondary waves - They are the next waves to be detected.
These waves move only through solids.
They move up and down or side to side, perpendicular to the direction in which the wave is moving.
Surface waves - It follow P and S waves and travel along the surface of the earth and thus cause the most damage.
Surface waves can be characterized as
Love waves - Faster and move the ground from side to side, and
Rayleigh waves - Roll like waves on the surface of oceans and lakes.
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