Earth's Interior and Seismic Activity

Historical Perspectives

• Five Centuries Ago: Earth was believed to be a uniform sphere of rock.
• Sir Isaac Newton: Proposed that Earth's interior is denser than surface rock.
• 1900s Earthquake Studies: Seismic data began to be used to explore Earth's interior.

Understanding Earth's Layers through Seismic Waves

• Seismic Waves: Used to understand Earth's interior structure by analyzing travel times to seismic stations worldwide.
• Three Chemical Layers:
  • Crust: Outermost, analogous to an egg shell.
  • Mantle: Intermediate layer, analogous to egg white.
  • Core: Innermost, analogous to egg yolk, but with distinct inner and outer parts.

Earth’s Layers

The Crust

• Composed mostly of 8 elements: Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium.
• Thin, ranging from 5-10 km (oceanic) to 75 km (continental).
• Difference in density and thickness forms oceans and continents.

The Mantle

• Composition: Similar elements as crust, different proportions.
• Upper Mantle: Cooler, brittle (50-120 km thick).
• Asthenosphere: Below upper mantle, plastic and malleable due to heat and pressure.
• Lower Mantle: Denser and hotter, constitutes 55% of Earth's volume.

The Core

• Outer Core: Liquid, vigorous convection generates magnetic field.
• Inner Core: Solid, denser due to pressure despite higher temperature.

Plate Tectonics

Lithosphere

• Combination of crust and upper brittle mantle.
• Rigid, moves in unison, ranges from 100 km (oceanic) to 200 km (continental).
• Site of earthquakes due to movements like compression and shearing.

Tectonic Plates

• Broken into lithospheric plates due to Earth's cooling surface.
• Plates float on more ductile asthenosphere.
• Driven by convection currents (temperature, pressure, gravity).

Geological Phenomena

• Earthquakes, volcanoes, and magnetic fields arise from Earth losing heat and converting thermal energy to mechanical energy.

Conclusion

• Seismic activity is crucial for understanding Earth's interior.
• Plate tectonics are driven by Earth's internal heat and are essential for geological activity on Earth's surface.⭕️