Geography (2217)
Topic 1 of 1Cambridge O Levels

Plate Tectonics & Earthquakes

Why Pakistan sits on a seismic hotspot

The Earth's crust is broken into large pieces called tectonic plates that float on the mantle.


Structure of the Earth:

  • Crust: Thin outer layer (5-70 km thick)
  • Mantle: Hot, semi-molten rock. Convection currents move plates
  • Outer Core: Liquid iron and nickel
  • Inner Core: Solid iron and nickel (5,500°C!)

    • Plate Boundaries:

  • Constructive (divergent): Plates move apart. New crust forms. Mid-Atlantic Ridge.
  • Destructive (convergent): Plates collide. One goes under (subducts). Creates mountains and volcanoes.
  • Conservative (transform): Plates slide past each other. Creates earthquakes.

    • Earthquakes:

  • Caused by sudden release of energy at plate boundaries
  • Focus: Point underground where earthquake starts
  • Epicentre: Point on surface directly above focus
  • Measured on Richter scale (logarithmic — each number is 10× stronger)
  • Seismometer detects and records earthquake waves

    • Effects of Earthquakes:

    Primary: Building collapse, ground shaking, cracks in ground

    Secondary: Tsunamis, fires, landslides, disease, homelessness

    Key Points to Remember

    • 1Earth's layers: Crust → Mantle → Outer Core → Inner Core
    • 23 plate boundaries: Constructive, Destructive, Conservative
    • 3Earthquakes measured on Richter scale (logarithmic)
    • 4Focus = underground origin, Epicentre = surface above focus

    Pakistan Example

    The 2005 Kashmir Earthquake

    Pakistan sits where the Indian Plate pushes into the Eurasian Plate — a destructive boundary that created the Himalayas and Karakoram! The devastating 2005 earthquake (7.6 on Richter scale) killed 87,000 people in Muzaffarabad and surrounding areas. The Indian Plate subducts under the Eurasian Plate, and the pressure buildup was released catastrophically. This is also why Pakistan has the world's second-highest mountain (K2, 8,611m) — the ongoing collision keeps pushing the land upward. Understanding plate tectonics isn't just theory — it's survival knowledge for Pakistan.

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