1.3.5 Patterns of earthquakes

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  • Patterns of earthquakes
    • Earthquake:
      • A vibration in the rocks of the Earth's crust and upper mantle caused by a dislocation of rocks along a fault.
    • Where?
      • Seismic areas: stresses are acting in the crust and upper mantle.
        • Mid-ocean areas
          • MOR: Shallow focus
            • Rising magma producing harmonic waves. Detected as earthquakes.
          • Axial rift systems: Shallow focus
            • Extension of crust forms normal faults. Movement along faults (subsidence) = earthquakes.
          • Transform fault: Shallow focus
            • Horizontal movement along faults.
        • Subduction zones
          • Deep ocean trench + fold mountains
            • Further inland foci are deeper (towards fold mountains) where 1 plate subducted beneath the other = benioff zone
            • Shallow under deep ocean trench and oceanic sides of fold mountains
      • Depth of focus
        • Shallow focus 0-70 km
        • Intermediate 70-300 km
  • Collision zones
    • Shallow and medium earthquakes along deep faults.
    • Conservative, slide past e/o = shallow.
    • Subduction zones
      • Deep ocean trench + fold mountains
        • Further inland foci are deeper (towards fold mountains) where 1 plate subducted beneath the other = benioff zone
        • Shallow under deep ocean trench and oceanic sides of fold mountains

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