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Earthquakes UPSC and APSC

Earthquakes UPSC and APSC
Earthquakes UPSC and APSC

  • An earthquake, in basic terms, refers to the seismic shaking of the Earth's surface. The occurrence is of a natural nature. The phenomenon occurs as a result of the liberation of energy, leading to the production of waves that propagate in a multidirectional manner.

  • Seismic waves, which are produced by seismic events such as earthquakes, propagate through the Earth and are detected and recorded by seismographs.

  • The seismic event originates at a point beneath the Earth's surface known as the hypocenter, while its corresponding position directly above on the Earth's surface is referred to as the epicenter.

Types of Earthquake and Causes

Fault Zones:

  1. The release of energy occurs along a fault. A fault refers to a distinct fracture in the Earth's crustal rocks, characterized by a dramatic displacement.

  2. Rocks situated along a fault exhibit a tendency to undergo movement in divergent directions. The cohesion between the rock layers is facilitated by the application of pressure from the overlaying strata, resulting in the interlocking of the rock surfaces due to the presence of friction.

  3. Nevertheless, the propensity of these entities to separate at a certain juncture surpasses the force of friction. Consequently, the blocks undergo deformation and ultimately experience sudden sliding past one another.

  4. The phenomenon described results in seismic activity, characterized by the sudden release of energy. Subsequently, energy waves propagate in a multidirectional manner.

Earthquakes UPSC and APSC

Tectonic Earthquakes:

Earthquakes UPSC and APSC

  1. Tectonic earthquakes are the most common type.

  2. Despite the Earth's apparent solidity when observed from its surface, it exhibits significant dynamism and activity in its subsurface regions.

  3. The Earth is composed of four primary layers, typically categorized as three: a solid crust, a predominantly solid mantle characterized by high temperatures, a liquid outer core, and a solid inner core.

  4. Tectonic plates, also known as lithospheric plates, undergo continuous movement as they traverse the underlying mantle layer, which exhibits a viscous or gradual flow.

  5. The continuous motion of tectonic plates induces strain on the Earth's lithosphere. When the magnitudes of stresses exceed a certain threshold, they give rise to fractures in the Earth's crust known as faults.

  6. The movement of tectonic plates induces concurrent displacements along fault lines. Therefore, the occurrence of earthquakes is attributed to the displacement of land along fault lines at convergent, divergent, and transform plate borders.

  7. The location at which seismic energy is discharged is sometimes referred to as the focus of an earthquake, or alternatively, it is known as the hypocenter. The energy waves propagate in many directions and ultimately reach the surface.

  8. The location on the surface that is closest to the focus is referred to as the epicenter. This entity is the initial one to encounter the oscillations. The point in question is situated precisely above the focal point.

Volcanic Earthquake

Volcanic Earthquake
Volcanic Earthquake

  1. Volcanic earthquakes are occasionally acknowledged as a distinct category within the realm of tectonic seismic activity. Nevertheless, these phenomena are limited to regions characterized by active volcanic activity.

  2. Volcano earthquakes refer to seismic events that arise from the alteration of stress within solid rock as a result of magma injection or withdrawal.

  3. These seismic events have the potential to induce land subsidence and generate significant ground fissures. Earthquakes can manifest when rock undergoes movement to occupy voids left by the absence of magma.

  4. Volcano-tectonic earthquakes do not necessarily serve as a reliable precursor to volcanic eruptions, as they can manifest at any given moment.

Human Induced Earthquakes

Human Induced Earthquakes
Human Induced Earthquakes

  1. In regions characterized by high levels of mining operations, occasional occurrences of roof collapses within underground mines have been seen, resulting in modest seismic disturbances. These seismic events are commonly referred to as collapse earthquakes.

  2. The occurrence of ground shaking can also be attributed to the detonation of chemical or nuclear explosives. These seismic events are commonly referred to as exploding earthquakes.

  3. Reservoir produced earthquakes are seismic events that take place in regions characterized by the presence of substantial reservoirs.

Earthquakes and their relationship to the depth of focus

  1. Earthquakes are categorized into three distinct zones, namely shallow, moderate, and deep, according to their depth, which spans a range of 0 to 700 kilometers.

  2. Shallow earthquakes often occur at depths ranging from 0 to 70 kilometers.

  3. Intermediate earthquakes are characterized by having a focal depth ranging from 70 to 300 kilometers.

  4. Deep earthquakes are characterized by their focal depths, which typically range from 300 to 700 kilometers.

Wadati–Benioff zone

Wadati–Benioff zone
Wadati–Benioff zone

  1. Earthquakes with depths ranging from 300 to 700 kilometers occur inside this particular zone.

  2. The region under consideration is characterized by subduction, a geological process in which one tectonic plate is forced beneath another. This tectonic boundary is frequently associated with seismic activity, since the contact between a descending oceanic crustal plate and a continental plate gives rise to frequent earthquakes.

  3. The zone in question is known for hosting a number of highly potent earthquakes.

  4. Earthquakes can arise from slip occurring along the subduction thrust fault or from slip on faults within the descending plate as it is drawn into the mantle.

Distribution of Earthquakes

  1. Earthquakes have the potential to occur in any geographical area and at any given time. However, historical data reveals that they tend to exhibit recurring patterns, mostly manifesting within three major seismic zones across the globe.

  2. The circum-Pacific seismic belt, widely regarded as the most significant earthquake belt globally, is situated along the periphery of the Pacific Ocean. This region is responsible for approximately 81 percent of the strongest earthquakes recorded on Earth.

  3. The geographical feature in question has been bestowed with the moniker "Ring of Fire".

  4. The presence of the belt is observed in regions where tectonic plates converge, specifically where plates composed predominantly of oceanic crust undergo subduction beneath another plate. Earthquakes occurring inside these subduction zones are mostly attributed to interplate slip and intraplate rupture phenomena.

  5. The Alpide earthquake belt, also known as the mid-Continental belt, spans across many regions including Java, Sumatra, the Himalayas, the Mediterranean, and stretches further into the Atlantic.

  6. The seismic belt in question encompasses around 17% of the most significant earthquakes globally, including those that have caused substantial devastation.

  7. The third notable belt is situated along the submerged mid-Atlantic Ridge. The ridge denotes the location where two tectonic plates are undergoing a process of divergence, forming a divergent plate boundary.

  8. The majority of the mid-Atlantic Ridge is situated at considerable depths beneath the ocean's surface, and it is geographically distant from areas of human habitation and development.

Measurement of Earthquakes


  1. Seismic waves are the vibrational manifestations by which the energy from an earthquake propagates within the Earth.

  2. Seismic waves can be measured by scientists using devices known as seismometers.

  3. The seismometer is capable of detecting seismic waves that occur beneath its location and afterwards records these waves as a sequence of zig-zags.

  4. The temporal, spatial, and magnitude characteristics of an earthquake can be ascertained by scientists through the analysis of data collected by a seismometer. Additionally, this record offers insights on the geological composition of the medium through which the seismic waves propagated.

  5. Earthquake events are classified based on either their magnitude or the strength of the seismic shock they produce. The scale used to measure the magnitude of earthquakes is commonly referred to as the Richter scale. The magnitude of an earthquake is directly associated with the amount of energy that is released during the seismic event. The magnitude is quantified using a numerical scale ranging from 0 to 10.

  6. The scale denoting seismic strength is attributed to Mercalli, a renowned seismologist of Italian origin. The intensity scale incorporates the observable damage resulting from the occurrence. The intensity scale spans from 1 to 12.

Seismic Waves (Earthquake Waves)

Seismic Waves (Earthquake Waves)
Seismic Waves (Earthquake Waves)

  1. Seismic waves refer to the propagating waves of energy that are generated as a result of seismic events, such as earthquakes or explosions. Seismic waves are the propagating forms of energy that traverse the Earth's interior and are detected and recorded by seismographs.

  2. Earthquake waves can be classified into two primary categories, namely body waves and surface waves.

  3. Body waves are produced as a result of the release of energy at the focal point and propagate in various directions, traversing the interior of the Earth. Therefore, the term "body waves" is derived.

  4. There exist two distinct categories of body waves. The seismic waves in question are commonly referred to as P and S-waves.

  5. P-waves exhibit a higher velocity compared to other seismic waves and are typically the initial arrivals at the Earth's surface. These seismic waves are commonly referred to as "primary waves" in scientific literature. The P-waves exhibit similarities to acoustic waves. They traverse various states of matter, including gas, liquid, and solid substances.

  6. Surface waves, namely S-waves, have a temporal delay upon reaching the Earth's surface. These seismic waves are commonly referred to as secondary waves. One crucial characteristic of S-waves is their exclusive ability to propagate solely through solid substances.

  7. The propagation of body waves within the Earth's interior leads to the interaction with the surface rocks, resulting in the generation of a distinct set of waves known as surface waves. These waves propagate along the surface.

  8. Surface waves are the final seismic waves to be recorded on seismographs. These waves have a higher level of destructiveness. The relocation of rocks is a contributing factor to the subsequent collapse.

  9. Therefore, the attributes of seismic waves hold significant importance. The study has facilitated scientists in comprehending the composition of the Earth's internal structure.

Effects of Earthquake

Effects of Earthquake
Effects of Earthquake

  1. Earthquakes are a naturally occurring phenomenon that poses a hazard to human populations and infrastructure. In the event of a seismic disturbance of significant magnitude, it has the potential to result in substantial harm to both human life and property. The subsequent are the instant perilous consequences of an earthquake:

  2. The occurrence of ground shaking.

  3. Differential ground settlement refers to the uneven vertical movement of the ground surface, typically caused by variations in soil conditions or external factors.

  4. The topic of concern is the occurrence of land and mudslides.

  5. The topic of discussion pertains to fires.

  6. The phenomenon of ground lurching

  7. Avalanches are natural disasters that occur when a mass of snow, ice, and debris

  8. Ground displacement refers to the movement or shifting of the Earth's surface, typically caused by various geological processes such as tectonic plate

  9. The occurrence of floods resulting from the failure of dams and levees.

  10. The phenomenon of structural collapse refers to the failure of a building or other man-made structure to maintain its integrity and stability, resulting in

  11. A tsunami is a natural disaster characterized by a series of large ocean waves caused by the displacement

Earthquake in India

Earthquake in India
Earthquake in India

  • India is considered to be a country that experiences a high frequency of earthquakes due to the existence of geologically active young fold mountains, namely the Himalayas.

  • India has been categorized into four seismic zones (II, III, IV, and V) through the utilization of scientific data pertaining to seismic activity, historical earthquake occurrences, and the tectonic configuration of the area.


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