Endogenic movements:Earthquake

There are two types of earth movements that led to development of present shape of earths interior and exterior and these movements are called -Endogenic and Exogenic movements. 

Basics about Endogenic and Exogenic movements-

A. Endogenic Movements-

• These are those movements that are caused due to internal forces of the earth. 

These are further divided into Two parts-

Diastrophic movements and Sudden movements. 

1.Sudden Movements

• These are the movements that are caused due to sudden deformation of Earth.

• This deformation can be due to Plate Tectonic ,Conventional currents etc.

Examples - 

• Earthquake and Volcanoes. 

2.Diastrophism 

• It refers to deformation of the Earth’s crust.

It is  further classified as follows-

Epeirogenic movements -

• These are continent forming movements like subsidence and upliftment. 

Orogenic movements-

• These are mountain building movements like folding and faulting. 

B.Exogenetic Movements-

• These are the movements that changes earth surface due to various forces rising above the earth surface like Wind,Water etc.

Example-

• Weathering,Erosion by ice,water etc.

Gradation-

• Levelling and smoothening of land surface is called gradation includes both degradation and aggradation. 

Degradation -

• When rocks are removed by scraping, scratching and cutting as a result of the process of erosion, thereby lowering the elevation of the land, it is called degradation.

• It includes actions like Weathering ,Erosion etc.

Aggradation

• Filling up of low-lying areas of depression by eroded material is called deposition. When the agents of gradation lose their force or have obstruction in their way then the deposition starts. 

In this section we will discuss about Sudden Endogenetic movements i.e. Earthquake and Volcanoes. 

• The sudden  vibration of earth surface due to formation of seismic waves is known as Earthquake. 

• These seismic waves are generated due to release of energy during tectonic movements. 

Some of the Terms related to Earthquake-

Focus(centrum) and Hypocentre :

• The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre. 

Epicentre:

• The point on the surface of the earth which is located nearest to the focus, is called epicentre.  It is a located directly above the focus.

Isoseismal Lines(related to intensity):

• These lines join points of equal intensity on the surface where the earthquake occurs. 

Homoseismal or coseismals lines(related to time):

• These are the lines drawn through the points at which the earthquake is recorded at the same time. 

Pleistoseistic region: 

• Located around the epicentre is the region where maximum destruction occurs as a result of an earthquake. 

Foreshocks :

• These are smaller earthquakes in the same area which comes after the larger earthquake. 

Causes of Earthquake-

There are Two major causes of Earthquake-

1.Tectonic Causes

• Due to the movement of tectonic plates there is release of energy which causes Earthquake. 

It is further divided as follows-

Due to Divergence of plates-

• Due to opposite movement of plats ,Faults are formed which releases some energy causing Earthquake. 

Due to Friction of plates-

• When plates moves toward each other or parallel to each other than due to friction or convergence there is formation of seismic waves. 

Elastic rebound Theory-

Elastic Rebound theory was propounded by Harry Fielding Reid after studying 1906 San Francisco earthquake faultline. 

The theory-

• As the Earth's crust deforms, the rocks which span the opposing sides of a fault are subjected to shear stress. Slowly they deform, until their internal rigidity is exceeded.

• Then they separate with a rupture along the fault; the sudden movement releases accumulated energy, and the rocks snap back almost to their original shape. 

2.Earthquake due to change on Earth surfaces-

The Earthquake can also occur due to changes on earth surface like-

• Blasting of mines and rocks. 

• Collapse of caves. 

• Heavy landslide on or below land surface. 

• Tsunami and floods etc.

3.Other causes

• It includes sudden bursting of Volcanoes ,Man made distruction like Atomic bomb,Reserviors etc.

• The Koynanagar earthquake occurred near the Koyna Dam reservoir in Maharashtra in 1967 . 

Classification of Seismic waves-

Seismic waves are of two types:

A. Body waves. 

B. Surface waves. 

A. Body waves . 

• These waves are generated when release of energy at the focus  and they move in all directions travelling through the body of the earth. 

Body waves are further classified into two types-

Primary waves or P-waves-

• The waves travel from the earthquake focus through Earth and the first wave to arrive is P-wave.

• P-waves are also referred as longitudinal or compressional waves  because they travel through solid, liquid or gaseous materials as a succession of compression and expansions and therefore, .

• P-wave are similar to sound waves . These types of waves have short wavelength along with high frequency.

• They are also called as pull or push waves.

• They can travel through all three mediums like gaseous, liquid and solid materials. 

Secondary waves or S-waves  -

• S-wave travels through solid rock at a little more than half the velocity of P-waves.

• They are also called as Shear waves and they displaces material at right angles to their path of travel.

• They do not travel through liquids and gasses.

• They are Transverse or transitional waves and have short wavelength and high frequency.

• There velocity changes with change in density of solid materials.

B. Surface waves

• On seismograph These types of waves are reported at Last. 

• These waves are more destructive.

• The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane confined to the Earth’s surface, like waves on the ocean and causes Crust and Trough. 

These waves are further divided into Two parts-

Love wave: 

• Love waves shake the surface side-to-side. 

Rayleigh wave:

• They are complex surface waves in which ground vibrates in a rolling, elliptical motion that diminishes as the depth increases partly in the direction of propagation and partly at right angles. 

Shadow Zone-

• There are some specific areas where the earth quack waves are not reported and these areas are called as Shadow Zone.

• Both P and S-waves were reported when seismographs  were placed within 105° from the epicentre. 

• The seismographs that were placed or  located beyond 145° from epicentre, recorded the arrival of only the P-waves,and there was no arrival of  S-waves.

• Thus, a zone between 105° and 145° from epicentre was identified as the shadow zone for both the types of waves.

• S-waves were not received beyond The entire zone from 105° .

• The shadow zone of P-wave is much smaller than that of the S-waves.

• The shadow zone of P-waves appears as a band around the earth between 105° and 145° away from the epicentre.

• The shadow zone of S-waves is very large and it covers approximately over 40 per cent of the earth surface. 

Types of Earthquake-

Based on Depth of Earthquake-

1.Normal or shallow depth earthquakes -

• It originate from within a depth of 50 km. Majority of the earthquakes in the past had been of this type.

2.Earthquakes of intermediate depth -

• It originate at a depth of 50 to 240 km. These are rare in occurrence but their effects are felt over a large area.

3.Deep-focus earthquakes-

•  It originate at a depth of several hundred kilometres (240 to 725 km) and are very rare phenomena. 

Based on Source of Origin

• Earthquake can also be classified as Natural Earthquake and Man-made Earthquake.

• Generally Man made earthquake are not that much dominating and also are less intense as comparison to the Natural Earthquake. 

Based on Causes for its formations-

• It includes tectonic earthquake (due to tectonic activity),Volcanic Earthquake(due to volcano )etc.

Measuring Earthquake-

There are two parameters that are measured for Earth quack I.e. magnitude and Intensity. 

The magnitude is related to the energy released during the Earthquake. 

The Intensity is related to damage caused by Earth Quack. 

Richter Scale-

• It is used to measure the magnitude of the E.Q.

• The magnitude is expressed in numbers, 0-10.

• 0 being lowest magnitude and 10 being highest.

Mercalli scale-

• It is used to measure the intensity of E.Q.

• It is named after Mercalli and he was an Italian seismologist.

• The range of intensity scale is from 1-12.

Effects of Earthquake -

• Ground displacement. 

• Structural collapse. 

• Tsunami . 

• Floods from dam and levee failures. 

• Faulting and Shaking. 

• Structural damage on Earth surface etc.

Distribution of Earthquake-

Pacific belt-

• This belt is also known as  Circum-Pacific seismic belt.

• About 81% of world’s largest earthquakes occur in the Circum-Pacific seismic belt.

• This belt includes the rim of Pacific plate and nearby plates and corresponds to the Pacific ‘Ring of Fire’.

• The slip between plates and rupture within plates in these subduction zones causes earthquakes.

Alpine or Mediterranean belt

• It extends from Java to Sumatra through Himalayas and Mediterranean and into Atlantic.

• This accounts for 17% of world’s largest earthquakes, including some of the most destructive such as the Andaman-Sumatra earthquake in 2004.

Mid Atlantic belt-

• It is the prominent earthquake belt and follows the submerged Mid Atlantic Ridge in Atlantic Ocean.

• This belt has not been particularly much destructive, as they occur far from populated areas.

Wadati Benioff zone is a zone of subduction along which earthquakes are common. The most powerful earthquakes occur along this zone .This zone is related to Plate convergence. 

Seismic Zones of India-

• India has been divided into four zones viz. zone V, IV, III and II according to the seismic zoning map of India prepared by Bureau of Indian Standards (BIS). 

• Risk of Earthquake decrease from zone V to Zone II. 

Zone V:

• It is the highest Eathquake prone xone of India. 

Areas-

• Parts of Jammu and Kashmir (Kashmir valley); Western part of Himachal Pradesh; Eastern part of Uttarakhand, Kutch in Gujarat; part of Northern Bihar; all northeastern states of India and Andaman & Nicobar Islands.

Zone IV:

•  Ladakh; Remaining parts of Jammu & Kashmir, Himachal Pradesh and Uttarakhand; Some parts of Haryana, Parts of Punjab; Delhi; Sikkim; northern part of Uttar Pradesh; small portions of Bihar and West Bengal; parts of Gujarat and small portions of Maharashtra near the west coast and small part of western Rajasthan.

Zone III: 

• Kerala; Goa; Lakshadweep islands; remaining part of Bihar; northern parts of Jharkhand and Chhattisgarh; parts of Uttar Pradesh and Haryana; remaining parts of Gujarat and Punjab; parts of West Bengal, western Rajasthan, Madhya Pradesh; parts of Maharashtra, Odisha, Andhra Pradesh, Telangana, Tamilnadu and Karnataka.

Zone II: 

• Remaining parts of Rajasthan, Uttar Pradesh, Gujarat, Haryana, Madhya Pradesh, Maharashtra, Odisha, Andhra Pradesh, Telangana, Karnataka and Tamilnadu.

59% of the land mass of India has been classified as prone to earthquakes of which -

• 11% is in very high risk zone V. 

• 18% in high risk zone IV. 

• 30% in moderate risk zone III. 

National capital of Delhi is in zone IV and Mumbai, Kolkata and Chennai are in zone III.

Some Factual Exam Oriented Questions on The Earthquake

What is an earthquake?

Answer: An earthquake is a natural phenomenon caused by the sudden release of energy within the Earth's crust.

How are earthquakes measured?

Answer: Earthquakes are measured using a device called a seismometer, which detects the waves generated by the earthquake and records them as seismograms.

What is the Richter Scale?

Answer: The Richter Scale is a numerical scale used to measure the magnitude of an earthquake.

What is the Mercalli Scale?

Answer: The Mercalli Scale is a numerical scale used to measure the intensity of an earthquake at a given location, based on the observed effects of the earthquake on people, buildings, and other structures.

What causes earthquakes?

Answer: Earthquakes are caused by the movement of tectonic plates, which can create stress and pressure in the Earth's crust, leading to sudden ruptures and the release of energy in the form of seismic waves.

Where do earthquakes occur most frequently?

Answer: Earthquakes occur most frequently along the boundaries of tectonic plates, where the movement and collision of plates create intense seismic activity.

How can earthquakes be predicted?

Answer: Earthquakes cannot be accurately predicted, but scientists can use data on past earthquakes and geological activity to estimate the likelihood of future earthquakes in a given area.

What is liquefaction?

Answer: Liquefaction is a process that occurs during an earthquake in which soil or sediment loses its strength and stiffness and behaves like a liquid, causing buildings and other structures to sink or topple.

What is an aftershock?

Answer: An aftershock is a smaller earthquake that occurs after a larger earthquake in the same area, often as the result of the release of built-up stress in the Earth's crust.

What is a tsunami?

Answer: A tsunami is a series of ocean waves caused by an earthquake, volcanic eruption, or other underwater disturbance.

What is the difference between the focus and the epicenter of an earthquake?

Answer: The focus of an earthquake is the point underground where the earthquake originates, while the epicenter is the point on the Earth's surface directly above the focus.

What is a seismic gap?

Answer: A seismic gap is an area along a fault line where little or no seismic activity has occurred in recent history, indicating the potential for a large earthquake to occur in the future.

What is a seismogram?

Answer: A seismogram is a record of the seismic waves generated by an earthquake, recorded by a seismometer.

What is a tectonic plate?

Answer: A tectonic plate is a large, moving section of the Earth's crust that interacts with other plates, creating seismic activity and other geological phenomena.

What is a subduction zone?

Answer: A subduction zone is an area where one tectonic plate is forced beneath another plate, often resulting in intense seismic activity and volcanic eruptions.