How tremors in Delhi are different from earthquakes in the Himalayan region?

For Preliminary Examination: Current events of national and international events

For Mains Examination: GS I - World Geography

Context:

Mostly, the tremors experienced in Delhi from time to time are from earthquakes that originate elsewhere, sometimes as far away as Afghanistan. Monday’s magnitude 4 earthquake was located in Delhi itself, somewhere close to the Dhaula Kuan area.

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What are tremors?

Difference between tremors and earthquakes

Key takeaways:

• Delhi is situated in a seismically active zone, making earthquakes in the region unsurprising. Over the past five years, several minor tremors, typically ranging in magnitude from 2 to 3 or lower, have been recorded in and around the city. These tremors are generally imperceptible to people but are detected by seismometers.
• According to India's official earthquake hazard map, Delhi falls under Zone 4, which is the second-highest classification in terms of earthquake susceptibility. This classification indicates that the city is expected to experience intensity levels equivalent to MSK-8 during an earthquake.
• The Medvedev-Sponheuer-Karnik (MSK) scale measures the intensity of an earthquake based on its impact rather than the energy released, which is represented by magnitude.
• In simpler terms, the MSK scale assesses how strongly an area is affected by an earthquake. The impact can vary even between locations that are equidistant from the epicenter due to differences in geological conditions.
• Being in Zone 4, Delhi is prone to significant structural damage in the event of a major earthquake. The most vulnerable areas in India fall under Zone 5, which corresponds to an intensity level of MSK-9 or higher.
• Delhi is part of the Aravalli-Delhi Fold Belt, a geologically active region stretching from southern and eastern Rajasthan to Haryana and Delhi. This belt is characterized by layers of rock that were folded and deformed by geological processes millions of years ago. The stress accumulated in these rock formations is occasionally released as earthquakes.
• Unlike the Himalayan region, where frequent seismic activity results from the collision of the Indian and Eurasian tectonic plates, the Aravalli-Delhi Fold Belt has become more geologically stable over time. Although tectonic activity in this region has significantly declined, some faults remain active, occasionally causing mild tremors.
• Geologists compare these occasional earthquakes to old scars that occasionally flare up. Historical geological processes shaped the region’s seismicity, but major activity has largely ceased.
• However, studies indicate that around 25 earthquakes with a magnitude of 2.5 or higher, including about five around magnitude 3.5, occur annually in and around Delhi.
• Recently, some residents reported hearing an unusual sound during an earthquake in Delhi, which was not commonly associated with previous tremors in the region. This led to speculation about the nature of the quake.
• In reality, earthquakes can produce sounds, though they are usually outside the range of human hearing.
• Since earthquakes generate energy waves that travel through the Earth, they can create low-frequency vibrations. While larger quakes may sometimes produce audible sounds, such occurrences are rare

Difference between tremors and earthquakes

Earthquakes are significant seismic events where the ground shakes due to the release of energy in the Earth's crust. They:

• Are larger in magnitude
• Involve the sudden movement of rock along a fault line
• Can cause major damage to structures and the landscape
• Are measured on the Richter or Moment Magnitude scales
• Often have noticeable foreshocks and aftershocks

Tremors are minor seismic events that:

• Are smaller in magnitude (typically less than 2.0 on the Richter scale)
• May be barely perceptible without instrumentation
• Usually cause little to no damage
• Can occur as:
  • Foreshocks (before a major earthquake)
  • Aftershocks (after a major earthquake)
  • Independent minor seismic events
  • Earth vibrations from other sources (volcanic activity, underground explosions)

Indian space programme breaks into 2025 in ‘mission mode’

For Preliminary Examination: Current events of national and international importance

For Mains Examination: GS III - Science & Technology

Context:

The PSLV-C60 mission laid the foundations for Chandrayaan-4 and the Bharatiya Antariksh Station. Forthcoming test flights will move India closer to human spaceflight, soon to receive a helping hand from a third launch pad at Sriharikota, continuing work on NGLV, and a change of guard at ISRO

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Polar Satellite Launch Vehicles (PSLV)

Geo Satellite Launch Vehicles (GSLV)

Key takeaways:

• On December 30, 2024, the PSLV-C60 mission launched from the Satish Dhawan Space Center (SDSC) in Sriharikota. Within 15 minutes, the rocket successfully placed the Space Docking Experiment (SpaDeX) satellites into a 475-km circular orbit at slightly different velocities.
• Kepler Aerospace, an Indian private company, partnered with ISRO to provide ground station-as-a-service support for the mission. The company simultaneously managed both SpaDeX satellites and delivered comprehensive mission support in less than a month.
• A Swiss firm specializing in space situational awareness, s2a systems, shared updates on the satellites’ separation distances via social media. On January 2, 2025, the satellites reached a separation of 10–20 km, referred to as far rendezvous conditions. By January 6, they began moving closer. Although ISRO initially planned a live webcast for January 7, it postponed the event before canceling it entirely.
• On January 8, ISRO reported an unexpected drift when the satellites’ separation was reduced from 500 m to 225 m. Consequently, the separation was reset to 6–8 km on January 9 to begin the docking process anew.
• By January 10, the satellites entered a ‘hold’ mode to maintain a distance of 1.5 km. Over the following days, the inter-satellite distance was progressively reduced: to 230 m on January 11, then to 105 m, 15 m, and finally 3 m by January 12. At this stage, ISRO temporarily increased the distance to 10.9 km to analyze sensor data before proceeding.
• On January 13, the satellites approached each other again, reaching 2.6 km apart, and by January 15, the distance was reduced to 900 m. Finally, on January 16, ISRO announced that the satellites had successfully docked and stabilized in orbit, marking the organization’s first in-orbit rendezvous and docking milestone. Post-docking, the satellites were controlled together from one unit, a critical capability for lunar and space station operations

GSLV and PSLV

 The Geosynchronous Satellite Launch Vehicle (GSLV) and the Polar Satellite Launch Vehicle (PSLV) are two of the most important satellite launch vehicles developed by the Indian Space Research Organisation (ISRO). They serve distinct purposes and are used based on mission requirements.

Here's a comparison of the two:

• The Polar Satellite Launch Vehicle (PSLV) is one of the most reliable and versatile satellite launch vehicles developed by the Indian Space Research Organisation (ISRO). Its primary function is to launch satellites into Polar Sun-Synchronous Orbits (SSO), making it ideal for earth observation and remote sensing missions.
• However, PSLV is not limited to SSO; it is also capable of placing satellites into Geostationary Transfer Orbits (GTO) and Low Earth Orbits (LEO), adding to its flexibility. The PSLV had its maiden flight on September 20, 1993, and since then, it has undergone numerous improvements to enhance its performance and reliability.
• The PSLV is a four-stage launch vehicle that alternates between solid and liquid propulsion systems. This unique design ensures a balance of power and precision during its mission. It has a payload capacity of up to 1,750 kg to SSO and up to 1,420 kg to GTO.
• Known as the "Workhorse of ISRO," the PSLV is celebrated for its high success rate and cost-effectiveness, making it a favored choice for launching satellites. Over the years, the PSLV has undertaken several landmark missions.
• Notable among these are Chandrayaan-1 in 2008, India’s first lunar exploration mission, and the Mars Orbiter Mission (Mangalyaan) in 2013, which made India the first country to reach Mars on its first attempt. In 2017, the PSLV-C37 mission set a world record by successfully deploying 104 satellites in a single mission, demonstrating its capability to handle complex operations.
• On the other hand, the Geosynchronous Satellite Launch Vehicle (GSLV) is a more advanced and powerful launch vehicle developed by ISRO. Its primary objective is to launch heavier payloads into Geostationary Transfer Orbit (GTO) and Medium Earth Orbit (MEO), although it is also capable of launching payloads into LEO. The GSLV made its debut on April 18, 2001, and since then, it has become a critical asset for India’s space program.
• The GSLV is a three-stage launch vehicle, incorporating a solid-propulsion first stage, a liquid-propulsion second stage, and a cryogenic third stage. The cryogenic stage, which uses liquid hydrogen and liquid oxygen, provides higher efficiency and thrust, enabling the vehicle to carry payloads weighing up to 5,000 kg to LEO and up to 2,500 kg to GTO. The development of an indigenous cryogenic upper stage was a major milestone for ISRO, marking a significant technological achievement.
• The GSLV has been instrumental in deploying India’s GSAT series of communication satellites, which are crucial for telecommunication and broadcasting services. It was also used in the Chandrayaan-2 mission in 2019, India’s second lunar exploration mission. Recently, in 2023, the GSLV successfully launched the NVS-01 satellite, which plays a vital role in India’s navigation system.
• Together, the PSLV and GSLV have propelled India’s space ambitions, each serving distinct purposes. While the PSLV excels in launching smaller satellites and multi-satellite payloads, the GSLV is designed for heavier payloads and higher orbits, making both vehicles complementary and indispensable to ISRO’s endeavors