Powerful earthquake strikes Taiwan
- Earthquake is a natural event caused due to release of energy, which generates waves that travel in all directions.
The emanation of energy occurs along a fault line which is a sharp break in the crustal rocks.
Types of Earthquakes:
- Tectonic earthquakes: The most common form of earthquake, is caused by the movement of loose fragmented pieces of land on the earth’s crust knowns as tectonic plates.
- Volcanic earthquake: The less prevalent compared to the tectonic variety, these earthquakes happen before or after the eruption of a volcano. It is caused when magma leaving the volcano is filled by rocks being pushed to the surface.
- Collapse earthquake: This earthquake occurs in underground mines. The main cause is the pressure generated within the rocks.
- Explosion earthquakes: The occurrence of this type of earthquake is artificial. High-density explosion such as nuclear explosions is the primary cause.
Causes of Earthquakes
- It is caused due to the tectonic movements of the earth.
- The energy release produces waves that travel in all directions.
- The point where energy is released is called the focus or hypocentre. It is generally located at a depth of 60 km.
- This causes a release of energy, and the energy waves travel in all directions.
- The point where the energy is released is called the focus of an earthquake or hypocentre.
- The point on the surface of the earth which is vertically above the focus is called the epicentre. It is the first place to experience the waves.
Types of Seismic Waves:
Earthquake waves are of two types — body waves and surface waves.
Body Waves are of two types; P wave and S wave.
- P-waves are also known as the Primary waves as they are the first waves to arrive at the surface.
- P-waves are like sound waves and tend to vibrate parallel to the direction of wave propagation. They elongate and squeeze the material through which they travel and creates density differences in the material through which they travel.
- They travel through all three mediums- solid, liquid, and gas.
- S- Waves arrive sometime after the happening of the Earthquake and they are called secondary waves.
- A significant characteristic of these S-waves is that they travel only through a solid medium.
- The direction of vibration of this S-wave is perpendicular to the direction of wave propagation, thereby creating crests and troughs in the material of their transmission.
B. Surface Waves:
Surface waves are of two types: Love waves and Rayleigh waves.
- Love waves have a horizontal motion that moves the surface from side to side perpendicular to the direction the wave is traveling.
- Love waves move faster than Rayleigh waves.
- Rayleigh waves cause the ground to shake in an elliptical pattern.
- This motion is like that observed in ocean waves.
- Of all the seismic waves, Rayleigh waves spread out the most, giving them a long duration on seismograph recordings.