Earthquake: Seismic Waves, Ground Lurching, Types of Earthquake UPSC

By BYJU'S Exam Prep

Updated on: September 6th, 2023

Earthquake is a natural event resulting in the Earth’s shaking. The main cause of an Earthquake is the release of energy from the Earth’s crust in the form of Seismic Waves that travel in all directions. These vibrations that arise from Earthquakes are measured on instruments known as seismographs. A hypocenter is a place below the Earth’s surface where the Earthquake commences. The epicentre, a point on the Earth’s surface just above the hypocenter, is where the sudden movement of the Earth is faced most strongly.

Understanding the causes, effects, and mechanisms of earthquakes is essential for the UPSC exam, as it falls under the Geography subject in the syllabus. It is crucial to study the various types of seismic waves, fault lines, and earthquake measurement scales for a comprehensive understanding of this natural phenomenon. Developing a solid understanding of earthquakes aids in analyzing their impact on human societies and devising strategies to mitigate their destructive consequences.


Earthquakes are natural phenomena characterized by sudden shaking and trembling of the Earth’s surface. They can occur at any time and are caused by various factors, such as the movement of tectonic plates, ground lurching, landslides, structural collapse, and ground displacement. In some cases, earthquakes can trigger secondary hazards like Tsunamis, which are large ocean waves that can cause significant damage when they reach coastal areas. These powerful geological events can have destructive consequences, impacting both human infrastructure and the natural environment.

Seismographs play a crucial role in studying earthquakes. These instruments record seismic waves, which are vibrations produced by earthquakes and propagate through the Earth. By analyzing the data from seismographs, scientists can determine the magnitude and location of an earthquake. The epicenter refers to the point on the Earth’s surface directly above the hypocenter, which is the actual location beneath the surface where the earthquake originates. Understanding the mechanisms and characteristics of earthquakes is essential for monitoring and predicting seismic activity, as well as implementing measures to mitigate their potential impact on vulnerable regions and populations.

Causes of Earthquake

The tectonic motions of the earth are what generate earthquakes. The focus, usually 60 kilometers, is where energy is unleashed. Waves that propagate in all directions are created when energy is released. The focus or hypocenter of an earthquake is the location where the energy is released. The epicenter is the location on Earth’s surface directly above the focus. It is the first location where waves are felt.

  • The rocks can sometimes overcome this friction as they tend to move apart. Eventually, the blocks suddenly bend out of the shop and slide over.
  • It causes the release of energy waves traveling in all directions and induces Earthquakes.
  • Ground lurching is an important phenomenon that is a consequence of Earthquakes. It demonstrates the horizontal movement of deposits, soil, or fills on vertical embankments as seismic activity affects uneven surface ruptures.

Types of Earthquakes

Depending upon the exact cause, there are three types of Earthquakes. The releasing of energy during an Earthquake takes place from a fault. This area is a sharp rupture in the rocks. Rocks alongside the fault tend to move in opposing directions. As the overlying rock layer press them, they get locked together due to frictional force. Following are the types of Earthquakes

  • Tectonic Earthquake: The most common type of earthquake is the tectonic earthquake, which occurs due to the movement of tectonic plates that make up the Earth’s surface. The constant motion of these plates generates pressure on the Earth’s crust, leading to cracks and faults. Earthquakes happen when the built-up stress is released and causes land to slip along fault lines at convergent, divergent, and transform plate boundaries. The epicenter, located directly above the focus, is the first point to experience the seismic waves.
  • Volcanic Earthquake: Volcanic earthquakes are specific to areas prone to volcanic activity. They are caused by the movement of solid rock due to the escape of molten rock (magma) from a volcanoes. These earthquakes can result in land subsidence and the formation of significant cracks in the ground. Although volcanic-tectonic earthquakes do not always lead to volcanic eruptions, they occur as rocks fill spaces previously occupied by molten rock. These earthquakes are associated with volcanic regions.
  • Human-Induced Earthquake: Human activities can also trigger earthquakes, primarily falling into two categories. Collapse earthquakes occur when the roof area of an underground mine collapses, leading to minor quakes. Explosion earthquakes, on the other hand, are caused by the outbursts of chemical or nuclear devices, which can shake the ground. Additionally, reservoir-induced earthquakes can occur in areas with large reservoirs, resulting from the filling of the reservoir and the associated changes in stress distribution.

Types of Earthquakes: Based on the Depth of Focus

Earthquakes are categorized into shallow, intermediate, and deep zones based on their depth ranging between 0 – 700 km. Deep Earthquakes (300-700 km) are generally produced in the Wadati–Benioff zone, where the interaction of a downgoing oceanic crustal plate against a continental plate occurs. The most powerful Earthquakes are known to appear under this zone.

Types Of Earthquakes Depth Of Focus
Shallow Earthquakes 0 – 70 km
Intermediate Earthquakes 70 – 300 km
Deep Earthquakes 300 – 700 km

Seismic Waves

The energy waves caused by Earthquakes are called seismic waves. These waves can travel all over the Earth and are studied on seismographs. Earthquake waves are predominantly of two kinds: body and surface waves. Body waves are generated due to the release of energy at the focus and are of 2 categories, i.e., P and S-waves. Thus, the attributes of the seismic waves are quite important. All these parameters aid scientists in understanding the Earth’s interior structure. Check the types of seismic waves in detail below.

  • P-Waves (Primary Waves): P-waves are the fastest seismic waves and are the first to be detected during an earthquake. They are compressional waves that travel through solid, liquid, and gaseous materials. P-waves cause particles to move in the same direction as the wave’s propagation, resulting in alternating compression and expansion of the material.
  • S-Waves (Secondary Waves): S-waves are slower than P-waves and follow them during an earthquake. These waves are shear waves that travel only through solid materials. Unlike P-waves, S-waves cause particles to move perpendicular to the wave’s direction, resulting in a side-to-side or up-and-down motion. S-waves are responsible for the majority of the shaking felt during an earthquake.
  • Surface Waves: Surface waves are the slowest seismic waves and travel along the Earth’s surface. They are primarily responsible for the most damaging effects of an earthquake, such as ground shaking and destruction of structures. Surface waves include two types: Love waves, which cause horizontal shearing motion, and Rayleigh waves, which cause both vertical and horizontal rolling motion.

Shadow Zone of an Earthquake

An area of the Earth’s surface known as a seismic shadow zone is one where seismographs cannot pick up direct P and/or S waves from an earthquake. This is because the Earth’s surface has liquid layers or structures.

Any liquid boundary or body can produce a shadow zone, but the core-mantle boundary, where P waves are refracted, and S waves are blocked at the liquid outer core, creates the most well-known shadow zone. For instance, seismic shadow zones can be produced by magma reservoirs with a high enough percentage of melt.

Effects of an Earthquake

An Earthquake is a natural disaster that results in heavy damage to the life and property of people if it is of high magnitude. Listed are the dangerous effects that an Earthquake can generate:

  • Ground Shaking – It is a vibration of the ground observed during an Earthquake.
  • Differential ground settlement – Only part of the floor is affected by the ground failure and causes more severe damage than uniform or tilt settlement.
  • Land and mudslides – The shaking of the Earth’s surface can disrupt land and mud.
  • Fires – The quakes can cause fire or volcanic eruption.
  • Ground lurching –The parallel movement of soil, sediments, or fills found on vertical embankments that create irregular ground cracks.
  • Avalanches – Tremors can affect a large amount of snow by causing them to slide quickly down the side of a mountain.
  • Ground displacement- It is another effect of an Earthquake that can cause the ground to change position in horizontal and vertical directions.
  • Floods from the dam and levee failures – Dams and levees are hydraulic structures that may break because of defaults or unexpected events. When an Earthquake occurs, water can be suddenly released and create a flood.
  • Structural collapse – Excessive weight placed on a faulty structure can cause a building to collapse.
  • Tsunamis are ocean waves activated by large Earthquakes that occur near or under the ocean.

How are Earthquakes Measured?

Seismic waves are energy from a quake that travels through Earth through vibrations. Researchers use instruments called seismometers to measure these seismic waves. The technique of calculating the intensity of an Earthquake is done in the listed manner.

  • Earthquakes Measurement By Seismometer: A seismometer is a device that identifies seismic waves and analyzes them as zig-zag series. This device helps scientists specify an Earthquake’s time, location, and intensity. It also helps to gather information about the rocks through which seismic waves travel.
  • Earthquakes Measurement By Richter Scale: Earthquake events are scaled according to the shock’s magnitude or intensity. The magnitude scale is known as the Richter scale, and the intensity scale is named after Mercalli.
Magnitude scale Intensity scale
It corresponds to the energy released during a quake. Measures the visible damage caused by the event.
Expressed in absolute numbers of 0-10 The range is from 1-12

Earthquake Disaster Management

Earthquakes are most active for a short time, just for a minute, but they can result in hazardous damage to life and property. Since Earthquakes strike without any intimation, to prevent large damage, it is crucial to recognize potential problems and indulge in systematic planning measures to reduce the impact afterward.

Before Earthquake During Earthquakes After Earthquakes
Store delicate items in low, closed cabinets. Try to take cover in a safe place by dropping down onto your hands and knees. Be watchful for aftershocks.
Hang heavy items, like mirrors, away from beds and sofas. Proceed into the open space or ground away from buildings or wires. Stay updated about the news, and listen to the radio or TV.
Repair cracks in walls and ceilings. If you are driving your vehicle, stop it quickly, and stay inside. Try to support the injured or trapped people.
Restore defective water or gas connections. Follow the guidance of emergency officials.
Locate safe places outdoors, away from buildings. Review your home and clean up spilt medicines or flammable liquids.

Earthquake Zones in India

The Bureau of Indian Standards has divided the country into four seismic zones: Zone II till Zone V. The 5th zone is considered the most active, whereas Zone II is the least, based on the past seismic history.

  • Zone-V: Entire northeastern stats, HP, Uttarakhand, Gujarat’s Rann of Kutch, a few parts of Jammu and Kashmir, Ladakh, Andaman & Nicobar Islands, and North of Bihar.
  • Zone-IV: Some parts of Jammu & Kashmir [not included in Zone V], small portions of the west coast of Maharashtra and Rajasthan, Bihar, Ladakh, Himachal Pradesh, north Uttar Pradesh, Union Territory of Delhi, Sikkim, West Bengal, and parts of Gujarat.
  • Zone-III: Some parts of Uttar Pradesh [not in Zone V and Zone IV], West Bengal, Punjab, Madhya Pradesh, Maharashtra, Odisha, Gujarat, Tamil Nadu, Bihar, Andhra Pradesh, Karnataka, Jharkhand, Rajasthan, Kerala, Goa, Lakshadweep islands, and Chhattisgarh.
  • Zone-II: Other parts of the country.

Earthquake UPSC

An earthquake is a potential natural hazard. The world does not inevitably endure significant shocks, as was previously noted. High-magnitude earthquakes, namely those that are 8 or more, happen just a few times per one to two years.

The topic of earthquakes and their types are extensively covered under the Geography syllabus for UPSC . Aspirants can refer to NCERT Books to understand the basic concepts, and then move to standard books to study the topic in detail. Moreover, questions pertaining to earthquakes have been repeatedly asked both in Prelims and Mains.

Earthquake UPSC Questions

Below we have provided some of the sample questions related to the topic for practice purposes. Candidates can refer to UPSC Previous Year’s Question Papers to practice more unsolved questions on the topic.

Question: The Elastic Rebound Theory is related to the origin of which among the following? (A) Volcanoes, (B) Oceans, (C) Earthquakes, (D) Mountains

Answer: Earthquakes

Question: What is the point on the fault where seismic waves are released called? (A) Hypocenter, (B) Epicenter, (C) Crest, (D) Ridge

Answer: Epicenter

For UPSC Mains

Question: Discuss the primary causes and mechanisms of earthquakes, highlighting the role of tectonic plate movements in their occurrence. Examine the various types of faults and their significance in seismic activities.

Question: Analyze the social, economic, and environmental impacts of earthquakes on affected regions. Discuss the role of disaster preparedness, early warning systems, and post-disaster management in reducing the vulnerability and enhancing the resilience of communities to earthquake disasters.

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