An earthquake also known as a quake or tremor is the shaking of the surface of the earth resulting from an immediate release of the energy in the earth’s lithosphere that creates seismic waves.
| Table of Contents 1. Characteristics of Earthquake 2. Types of Earthquake 3. Causes of Earthquake 4. Effects of Earthquake 5. Body Waves 5.1 Primary 5.2 Secondary Shadow Zone Measurement 7.1 Magnitude Scale 7.2 Intensity Scale |
Characteristics of an Earthquake
- All-natural earthquakes occur only in the lithosphere.
- An earthquake is simply the shaking of the earth’s crust.
- It is caused due to the sudden energy release, which triggers the waves that travel in all directions.
- The effusion of energy occurs along a fault.
- A fault is a fracture or crack between two blocks of rock.
- Rocks along a fault generally move in opposite directions.
Types of Earthquakes
- Tectonic earthquake: The most common form of an earthquake is caused by the sudden movement of loose fragmented pieces of land on the earth’s crust which is known as tectonic plates.
- Volcanic earthquake: The less widespread compared to the tectonic type, these earthquakes happen before or after the eruption of a volcano. It is caused when magma released from the volcano is filled by rocks being pushed to the surface.
- Collapse earthquake: This earthquake occurs at the underground mine level. The main cause of this earthquake is due to pressure generated within the rocks.
- Explosion earthquakes: The occurrence of this type of earthquake is an artificial form. High-density explosions such as nuclear explosions are the primary cause of this earthquake.
Causes
Causes of Earthquakes
- It is caused due to the tectonic movements of the earth’s surface.
- It is caused due to the energy release produced by waves that travel in all directions.
- The point where energy is released is called the focus or hypocenter. It is generally located at a depth of 60 km on the earth’s surface.
- This causes a release of energy and the energy waves that travels in all directions.
- The focus of an earthquake is the point where the energy is released.
- The epicentre is the first place where the waves are created, the surface of the earth which is vertically above the focus point is called the epicentre.
Effects of Earthquake
- Shaking and ground eruption.
- Soil liquidation. That is, the soil turns into a fluid-like mass during earthquakes.
- An earthquake may cause injury and loss of life to society, road and bridge damage.
- Landslides in the hilly areas.
- Earthquakes can cause fires by damaging electrical power or gas lines.
- Tsunami.
- Floods may be one of the effects of earthquakes if dams are damaged. Earthquakes may cause damage to dam rivers, which collapse and cause floods.
Body Waves
Body Waves
A body wave is also called a seismic wave that gets into the interior surface of the earth, as opposed to surface waves that travel on the earth’s surface. P and S waves are the two different body waves.
Each type of wave shakes the earth’s surface in different ways. Body waves travel through the interior part of the Earth along paths controlled by the material properties in terms of density and modulus.
The density and modulus vary according to the temperature, composition, and material phase. This effect parallels the refraction of light waves. Two different types of particle motion result in two types of body waves: Primary and Secondary waves.
These waves can travel through any type of material on the earth’s surface, including fluids, and can travel nearly 1.7 times faster than the S-waves. In the air, they take the speed and form of sound waves; hence they travel at the speed of sound. Typical speeds are 330 m/s in air, 1450 m/s in water, and about 5000 m/s in granite.
Body Waves: Secondary Waves
Secondary waves (S-waves) are shortening waves that are crossway in nature. Following an earthquake, S-waves arrive at seismograph stations after the faster-moving of P-waves and displace the ground vertical to the direction of propagation.
Depending on the transmitting direction, the wave can go through on different surfaces; for example, in the case of S waves that travel horizontally, the ground moves differently to one side and then the other.
S-waves can travel only through solids, liquids, and gases that do not support shear stresses. S-waves are slower than P-waves, and speeds are typically around 60% of that of P-waves on any surface. Shorten waves will not travel through liquid substances, so the absence of the S-wave in the earth’s outer core surface suggests a liquid state.
Shadow Zone
- The shadow zone is that portion of the earth in the earthquake that does not receive any direct P-waves. It is from the angular distances of 104 to 140 degrees from the given earthquake.
- Shadow zones are formed when the liquid core stops the S waves and refracts the P waves.
- A zone between the epicentre’s 105-145 degrees is found to be a shadow zone for both the waves. It appears as a band away from the epicentre,
- Beyond 105 degrees of the epicentre, the entire zone is free of the S-waves.
- S-waves have larger shadow zones than P-waves.
Measurement
Measurement
All earthquakes are different from each other in their intensity and magnitude. The instrument used for the measurement of vibrations is known as Seismograph.
Magnitude scale
- The magnitude of the earthquake is measured by the equipment called the Richter scale.
- The energy released during an earthquake is expressed in numbers out of 0 to 10.
Intensity scale
- The intensity of an earthquake is measured by the equipment called the Mercalli scale.
- It measures the tangible damage caused by the earthquake.
- It is expressed in the range from 1 to 12.
