Chapter - 3
Internal Structure of the Earth
️ ️ Earth :-
Earth is the only planet in the solar system on which life exists and it is the third planet under its position, it is also called the blue planet, because 71% water is found on the earth.
️ Internal structure of earth :-
We can divide the sources into two parts , whose role is prominent in understanding the internal structure of the earth .
Direct Source: - Under this, the evidence obtained from mining and the objects emanating from the volcano comes.
Indirect source: - Under it
- difference in temperature, pressure and density in the interior of the earth
- meteorite from space
- gravity
- Earthquake related activities etc.
Seismic waves:- Primary waves and secondary waves are also helpful in understanding the Earth. This chapter is also helpful in understanding the three layers inside the earth and the landforms created by volcanoes.
Layers of the Earth's internal structure :-
The internal structure of the earth is mainly divided into three parts :-
- (1) Earth's crust
- (2) Mantle
- ( 3 ) core
️ Earth's crust :-
This is the outermost part of the earth . It is 30 km from the ground . m. depth is found. The density of the rocks of this layer is 3 grams per cube. m. Is .
️ Mantle :-
The part below the earth's crust is called the mantle, this part starts from the bottom of the earth's crust and covers a distance of 2900 km. m. to the depth. The crust and the upper part of the mantle together form the lithosphere . The lower part of the mantle is in a solid state . Its density is about 3.4 per cubic cm. m. Huh .
️ Core :-
There is a core at the bottom of the mantle, which we divide into two parts, the inner and outer core . The outer core is in liquid state . While the inner core is solid. Its density is about 13 grams per cubic cm . The core is made of heavy materials like nickel and iron .
️ Parts of Earth's Crust :-
The depth of the earth's crust is 30 km below the surface. Till then . It is divided into two parts :-
a) Continental crust or Sial :- 20 km. This thick layer is mainly composed of silicate and lighter minerals such as aluminium. Therefore it is also called Sial (Si = Silica and AI = Aluminum) . Its density is low.
b) Oceanic layer or Sima: - This layer is 20 – 30 km. m. It is found at the average depth of which is mainly composed of basalt. It is heavier than sial in density. Magnesium minerals are also abundant in this layer along with silicate, hence it is also called Sima.
Earthquake: -
Earthquake simply means shaking of the ground or shaking of the earth. In other words, the vibration of the earth which started with a sudden jerk is called earthquake. Earthquake is a natural disaster. The following are the outbreaks caused by an earthquake:-
- Land shaking.
- Ground motion
- Landslide / mudslide.
- Soil liquefaction.
- Surface displacement
- Avalanche.
- The occurrence of floods due to rupture of dams and embankments.
- Ignite .
- Demolition of buildings and collapse of structures.
- generation of tsunami waves.
- falling of objects
- Leaning of the ground to one side.
Why does the earth vibrate?
The rocks on either side of the fault lying in the earth's surface move in the opposite direction. Where the upper rock blocks exert pressure. Their friction holds them together. Nevertheless, due to the tendency of separation, the effect of friction is reduced at a time, as a result of which the rock blocks get deformed and suddenly slide in opposite direction to each other. This releases energy and energy waves travel in all directions. This causes the earth to vibrate.
️ Main types of earthquake :-
On the basis of the factors of origin of earthquake, earthquakes are divided into the following five categories :-
Tectonic Earthquake: - Generally, tectonic earthquakes are more frequent. These earthquakes are generated due to the movement of rocks along the fault bed. For example, the main reason for this is the collision of continental, oceanic plates with each other or moving away from each other.
Volcanic Earthquake: - Only a specific class of tectonic earthquake is considered a volcanic earthquake. These earthquakes are mostly confined to active volcanic areas.
Collapse Earthquake: - In mining areas, sometimes the roof of underground mines collapses due to excessive mining work, due to which mild tremors of earthquake are felt. These are called fall earthquakes.
Explosion Earthquake: - Sometimes there is vibration in the ground due to nuclear and chemical explosions, such tremors are called explosion earthquakes.
Reservoir induced Earthquake: - The earthquakes which come in the areas with large dams are called dam induced earthquakes.
Types of seismic waves: -
There are two types of seismic waves :-
- geological waves
- Surface waves
️ Geologic Waves :-
These waves originate from the center of origin in the earth and go in different directions. These waves interact with surface rocks and turn into surface waves.
There are two types of geologic waves .
P waves (primary waves) like spring: - These waves pass through all the three types of medium gas, liquid and solid. These are the fast moving waves which reach the surface first.
S waves (secondary waves) (similar to the twitch of a rope): - These waves can pass only through hard and solid medium. They reach the surface only after P waves, due to these waves not passing through the liquid, it is helpful for scientists to understand the earth.
P waves exert pressure on the material in the same direction as it travels. S waves produce vibrations at right angles to the direction of the wave. Surface waves are the last recorded on the seismograph and are the most destructive.
Ground waves: -
These waves are more effective on the surface. Their intensity decreases with depth. New waves are generated due to the interaction between geologic waves and surface rocks. Which are called surface waves.
These waves move along with the surface. The velocity of these waves changes when they pass through materials of different densities. Most of the loss of life and property on the surface is caused by these waves. For example, breaking of buildings and dams and subsidence of the ground etc.
Difference between primary waves and secondary waves :-
Primary Waves :-
- 'P' waves are fast moving waves and reach the surface first.
- 'P' waves are like sound waves.
- These waves can pass through all three types of substances, gas, solid and liquid.
- The direction of vibration in 'P' waves is parallel to the direction of the generated waves.
- They cause contraction and expansion in rocks.
️ Secondary Waves :-
- 'S' waves move slowly and reach the surface after 'P' waves.
- 'S' waves are like ocean waves.
- These waves can only pass through solid matter.
- The direction of vibration in 'S' waves is at right angles to the direction of the waves.
- They generate bulges and troughs in rocks.
Seismic shadow areas: -
Seismic waves arriving from distant places are recorded on the seismic recorder. However, there are some areas where no seismic wave is recorded. Such areas are called seismic shadow zones.
The shadow area of one earthquake is different from that of another earthquake. The recording of 'P' and 'S' waves gives a clear indication of the shadow region.
It is observed that 'P' and 'S' waves are recorded within 105 from the epicenter. But after 145 only waves are recorded.
No wave is recorded between 105 to 145 from the epicenter, so this region acts as a shadow region for both types of waves.
Although the shadow region of 'P' waves is less than that of 'S' waves because 'P' waves are not visible only from 105 to 145°, but 'S' waves are not visible anywhere after 105, thus The shadow area of 'S' waves is larger than that of 'P' waves.
What is the difference between Batholith and Lacolith?
Batholith : - It is a domed cooled mass of magma in the earth's crust which is many. m. It is spread over a vast area in depth.
Lacoliths: - Large domed bodies of magma found at great depths have a flat bottom and a tube (from which the magma comes up) is connected to the magma source. The main difference between these two landforms is their depth.
️ Volcano :-
Volcano is an accidental event on earth. Due to this there is a sudden explosion on the earth's surface, through which lava, gas, smoke, ash, pebbles, stones etc. come out. The exhaust of all these things is through a natural tube which is called drain channel. Lava makes a hole to come to the surface, which is called a hole or crater.
️ Types of Volcanoes :-
There are mainly three types of volcanoes
Active Volcano :-
In this type of volcano, eruptions and eruptions often happen, their mouth is always open. Italy's Etna volcano is an example of this.
Dormant Volcano :-
This type of volcano would not have erupted for a long time, but its possibility remains. Whenever such volcanoes become active suddenly, they cause immense loss of public money. Italy's Vesuvius volcano is a prime example of this.
Extinct Volcano :-
Eruptions in this type of volcano usually stop and there is no possibility of eruption in future also. The Popa volcano of Myanmar is a prime example of this.
️ Process of formation of the following figures made by volcano :-
- caldera
- Cinderella
️ Caldera :-
When volcanoes are very explosive, instead of building a high structure, they blew up the protruding part and a huge crater is formed there which is called a caldera.
Cinderella: -
When the tendency of the volcano is less explosive, the lava comes out of the drain like a fountain and gets deposited in the form of a cone near the exit which is called cinder cone.
Intrusive shapes formed by volcanoes: -
- stitch
- Sheet
- dike
Seals and sheets: -
When the lava in the earth's surface cools in the form of a sheet in the horizontal plane and this layer is very thick, then it is called sil, when this layer is thin then it is called sheet.
️ Dyke :-
The flow of lava sometimes cools down in a crack in the ground and freezes. This crack occurs at right angles to the surface. This wall-like structure is called a dike.
