1.5 Physical Conditions of the Earth’s Interior

Case Study 1: InSight Mission & Seismic Profiling of Mars (Analogue to Earth’s Interior Studies)

• Models/Theories:
  • Seismic Wave Propagation Theory
  • Layered Earth Model (Mohorovičić Discontinuity, Gutenberg Discontinuity)
• Recent Data (2022–2023):
  • NASA’s InSight Mars Mission used seismometers to measure P- and S-waves to infer Mars’s crust-mantle-core structure, aiding comparative geophysical models for Earth.
  • Earth: Inner core temperature ~5200°C, pressure ~3.6 million atm; crustal thickness: continental (30–70 km), oceanic (5–10 km)
• Spatial Variation:
  • Earth’s crust varies: thickest under Himalayas (up to 70 km), thinnest under oceans (~5 km)
  • Mantle convection varies: active under mid-ocean ridges, stable beneath cratons.
• Temporal Variation:
  • Seismic tomography from 2000 to 2023 shows increased resolution in imaging subducted slabs and mantle plumes (e.g., Hawaii, Iceland).
• Source:
  • NASA JPL (2023), Nature Geoscience, Frontiers in Earth Science, and DownToEarth (“Deep Earth Imaging: New Frontiers”, Oct 2023)
• Insight:
  • Comparative seismology improves understanding of Earth’s internal heat flow, validating the Layered Earth Model and linking it to plate tectonics and volcanism.

Case Study 2: Indian National Seismic Zone Mapping – Crustal Variation Study

• Models/Theories:
  • Isostatic Compensation (Airy-Heiskanen Model)
  • Plate Tectonics and Seismic Zoning
• Recent Data (2023):
  • BARC and GSI seismic profiles show lower crustal thinning under Indo-Gangetic Plain (35–40 km) and thicker crust beneath Peninsular Shield (up to 55 km).
  • Heat flow values: high in Western Ghats (120–150 mW/m²), low in Bundelkhand (~40 mW/m²).
• Spatial Variation:
  • Crustal thickness across India:
    • Himalayas: 65–70 km
    • Peninsular Plateau: ~45–50 km
    • Coastal Plains and Plains: 30–35 km
• Temporal Variation:
  • No direct short-term variation, but mapping has improved over time.
  • Upgraded seismic zoning maps (Zone V includes Northeast, Kashmir Valley, parts of Bihar and Gujarat).
• Source:
  • PIB (April 2023), BARC Seismology Report, Earthquake Hazard Atlas of India, Economic and Political Weekly
• Insight:
  • Crustal and mantle studies offer crucial input for hazard zoning and tectonic modeling. Validates isostatic and plate tectonic perspectives in applied geophysics.