CORE Key Points at a Glance

  1. 1

    Earthquake — Definition and Structure

    • Sudden release of energy in Earth's crust or mantle due to movement along a fault
    • Creates seismic waves: P-waves, S-waves, Surface waves
    • Focus/Hypocenter — underground point of energy release
    • Epicentre — point directly above the focus on the surface
  2. 2

    Earthquake Measurement Scales

    • Richter Scale (logarithmic, 1935) — each unit = 10× ground motion amplitude, ~32× energy release
    • Moment Magnitude Scale (Mw) — now the scientific standard globally
    • Modified Mercalli Intensity Scale (I–XII) — measures felt shaking intensity at specific locations
  3. 3

    Circum-Pacific Belt — Ring of Fire (PYQ 2021)

    • Encircles the Pacific Ocean for ~40,000 km; accounts for ~80% of all world earthquakes and ~75% of all active volcanoes
    • Extends: New Zealand → East Asia (Japan, Philippines, Indonesia) → Alaska → American Pacific coasts (Cascades, Andes)
    • Most likely sub-topic to reappear in 2026
  4. 4

    Earthquake Classification by Depth of Focus

    • Shallow-focus (0–70 km) — most destructive; energy reaches surface quickly
    • Intermediate-focus (70–300 km) — moderate surface effect; along subducting slabs
    • Deep-focus (300–700 km) — felt over wide area; less catastrophic at surface; occur at subduction zones
  5. 5

    Volcanoes by Activity Status

    • Active — recently erupted (Etna, Stromboli, Kilauea)
    • Dormant/Sleeping — no recent eruption but not extinct (Mt. Rainier, Vesuvius)
    • Extinct — no likelihood of eruption (Edinburgh Castle Rock, Saddleback)
    • India's only active volcano: Barren Island (Andaman Sea, last major eruption 2017); Narcondam is dormant
  6. 6

    Earthquake Types by Cause

    • Tectonic earthquakes — most common (~90%); caused by plate movement along faults
    • Volcanic earthquakes — associated with magma movement; precede eruptions
    • Collapse earthquakes — cave or mine roof collapse; small, local
    • Reservoir-induced seismicity — Koyna dam (1967, Richter 6.5) — India's largest reservoir-induced earthquake; 180+ deaths
  7. 7

    Tsunamis — Key Facts

    • Seismic sea waves triggered by submarine earthquakes, underwater landslides, or volcanic eruptions
    • Speed: 700–900 km/h in open ocean; wave height amplifies dramatically near shore
    • 2004 Indian Ocean Tsunami (26 Dec, Mw 9.1–9.3, epicentre off Sumatra): 2.27 lakh deaths in 14 countries
    • Triggered by Sunda Megathrust fault; waves reached 30 m height in Banda Aceh
  8. 8

    India's Seismic Zones (BIS IS-1893)

    • India divided into Zones II, III, IV, and V (Zone V = highest risk; Zone I deprecated)
    • Zone V (very high seismicity): entire northeast, J&K, Himachal Pradesh, Uttarakhand, northern Bihar, Andaman
    • Rajasthan: mostly Zone II–III (moderate-low); Jaisalmer area is Zone II (lowest)
  9. 9

    Major Recent Earthquakes for RPSC

    • Nepal (April 2015, Mw 7.8, ~9,000 deaths)
    • Türkiye-Syria (Feb 2023, Mw 7.8+7.7, ~58,000 deaths)
    • Japan 2011 (Mw 9.0 Tōhoku, 15,000+ deaths, Fukushima nuclear disaster)
    • Gujarat Bhuj (26 Jan 2001, Mw 7.7, ~20,000 deaths)
  10. 10

    Volcanic Products

    • Lava — molten rock at surface; temperature 700–1,200°C
    • Magma — molten rock below surface
    • Pyroclastic material — tephra, bombs, lapilli, ash
    • Volcanic gases — SO₂, CO₂, H₂S, water vapour; Lahars — volcanic mudflows
    • Basaltic lava flows at 10–30 km/h; rhyolitic lava barely moves (very viscous)
  11. 11

    Mediterranean-Himalayan (Alpide) Belt

    • Second major earthquake/volcanic zone; accounts for ~15% of world earthquakes
    • Runs from Atlantic → Mediterranean → Middle East → Himalayas → Southeast Asia
    • Caused by Africa-Eurasia and Indian-Eurasian plate collisions
    • Major events along this belt: Bhuj 2001, Nepal 2015, Turkey 2023
  12. 12

    Positive Impacts of Volcanoes

    • Fertile soils — basaltic volcanic soils richest for agriculture; Java/Indonesia rice productivity exceptional
    • Geothermal energy — Iceland generates 66% electricity and 90% home heating from geothermal
    • Mineral deposits — copper, gold, sulphur associated with volcanic activity
    • New land creation — Hawaiian Islands created entirely by volcanic activity

PREDICTED Predicted RAS Questions

Based on PYQ trends and 2026 syllabus analysis

1 5M Describe the Circum-Pacific belt of volcanoes. 5 marks · 50 words

Model Answer

The Circum-Pacific Belt ("Ring of Fire") encircles the Pacific Ocean for 40,000 km, accounting for ~80% of world earthquakes and ~75% of active volcanoes. It extends from New Zealand through Indonesia, Philippines, Japan, Kamchatka, Alaska, and down the Americas to Chile. Formed by Pacific Plate subducting under surrounding plates, creating island arcs and explosive composite volcanoes (Fuji, Pinatubo, Krakatoa, Andes chain).

~50 words • 5 marks

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