Daily Mains Question - GS 1 - 14th October 2025
- TPP
- Oct 14
- 3 min read
Welcome to your Daily UPSC Mains Answer Writing Practice – GS Paper 1 (Geography | Geophysical Phenomena – Earthquakes and Plate Tectonics).
Today’s question explores the concept of Deep-Focus Earthquakes and their distinction from Shallow-Focus Earthquakes in terms of origin, depth, and surface impact. Earthquakes, among the most dynamic endogenic processes, result from the sudden release of accumulated stress along geological faults or plate boundaries, producing seismic waves that shape the Earth’s surface and influence human settlements.
Understanding the depth distribution of earthquake foci provides crucial insights into the Earth’s internal structure, plate boundary interactions, and subduction dynamics. While shallow-focus earthquakes often cause catastrophic surface damage due to their proximity to the crust, deep-focus earthquakes—occurring at depths of up to 700 km—offer valuable clues about mantle processes and the behavior of subducting slabs within the lithosphere-asthenosphere system.
For aspirants, this topic aligns directly with GS Paper 1 themes under Physical Geography, particularly “Distribution of Key Natural Hazards and Geophysical Phenomena”, and invites integration of concepts from plate tectonic theory, seismology, and disaster geography—enhancing conceptual clarity and analytical depth in answer writing.
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QUESTION
What are Deep-Focus Earthquakes and how do they differ from Shallow-Focus Earthquakes in terms of their origin and impact?
Answer: An earthquake is the sudden release of energy in the Earth’s lithosphere that creates seismic waves, resulting in ground shaking. Most earthquakes are tectonic in origin, caused by movements of lithospheric plates along faults or plate boundaries. The focus (hypocenter) of an earthquake is the point within the Earth where rupture starts, and the epicenter is the point directly above it on the surface.
Classification of Earthquakes by Depth of Focus
Type of Earthquake | Depth (km) | Common Occurrence Zone |
Shallow-focus | 0–70 km | Mid-ocean ridges, transform faults, continental rifts |
Intermediate-focus | 70–300 km | Subduction zones |
Deep-focus | 300–700 km | Subduction zones beneath convergent plate boundaries |
Earthquakes deeper than 70 km are termed deep-focus earthquakes, occurring mainly within subducting slabs as they descend into the mantle.
The deepest recorded earthquake occurred at a depth of about 700 km beneath the Izu-Bonin trench near Japan.
Origin and Mechanism
1. Shallow-Focus Earthquakes:
Originate in the upper crust (0–70 km).
Result from frictional slip along faults or crustal deformation.
Common along transform boundaries (e.g., San Andreas Fault, California) and divergent boundaries (e.g., Mid-Atlantic Ridge).
2. Deep-Focus Earthquakes:
Occur within subducting slabs descending into the asthenosphere or upper mantle.
Caused by dehydration of minerals and phase transitions within the slab, producing internal stresses.
Found along convergent boundaries—notably the Pacific Ring of Fire, Japan Trench, Peru–Chile Trench, and Hindu Kush region.
Differences between Deep and Shallow-Focus Earthquakes
Aspect | Shallow-Focus Earthquakes | Deep-Focus Earthquakes |
Depth | 0–70 km | 300–700 km |
Location | Along crustal faults, mid-ocean ridges, transform and rift zones | Within subducting oceanic plates at convergent boundaries |
Energy Release | High surface energy, causing intense ground shaking | Energy dissipates before reaching surface; less destructive |
Impact | Major damage to life and property (e.g., 2015 Nepal, 2001 Bhuj) | Minimal surface damage due to large depth |
Seismic Waves | Short travel distance, high intensity | Long travel distance, low surface intensity |
Tectonic Setting | Divergent and transform plate boundaries | Convergent (subduction) zones |
Significance of Earthquake Depth Studies
Helps understand plate tectonics and mantle processes.
Provides insights into subduction zone geometry and lithospheric recycling.
Crucial for seismic hazard assessment and engineering design codes in tectonically active regions like the Himalayas, Japan, and Indonesia.
Case Study: The Himalayan Region
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Deep-focus and shallow-focus earthquakes represent distinct tectonic processes within the Earth. While shallow-focus earthquakes pose the greatest hazard due to their proximity to the surface, deep-focus earthquakes offer valuable insights into subduction dynamics and the Earth’s interior structure. Understanding these variations is essential for seismic risk mitigation and for deepening our knowledge of plate tectonics and mantle geodynamics.
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