Faults

• Faults


  Breaks on earth's surface due to displacement of rock layers
• Not all fractures are considered as faults
• Characteristics of faults


  • Parts (fault line, dip, hanging wall, footwall)
  • Types (dip-slip, strike-slip, oblique)

  
• Tectonic plates


  Large pieces of rocks that make up the Earth's crust

  
• Asthenosphere


  Upper part of the mantle, partly molten, allows the movement of overriding plates at relatively slow rates
• Fault


  Fracture along which block of rocks have moved, found at the boundaries of tectonic plates

  
• Parts of a fault

  • Fault line (trace of the fault)
  • Dip (angle that the fault cuts through the soil layers)
  • Hanging wall blocks (portion above the fault)
  • Footwall blocks (surface below the fault)

  
• Dip-slip faults


  Movement of blocks is parallel to the dip of the fault surface
• Normal fault


  • Formed by tensional stresses that pull rocks apart, hanging wall moves down relative to the footwall, associated with divergent plate boundaries

  
• Horsts and grabens


  • Alternating uplifted (horsts) and down-dropped (grabens) blocks
• Reverse fault


  • Formed by compressional forces that push the plates towards each other, hanging wall moves upward relative to the footwall

  
• Thrust fault


  • Type of reverse fault whose dip is less than 45 degrees
• Strike-slip fault


  • Result of the sideways movement of blocks of rocks, blocks move laterally
• Oblique fault


  • Has both dip-slip and strike-slip components, formed by shear stress, and tensional or compressional stress
• Types of faults observed on a large scale

  • Strike-slip fault in San Andreas Fault
  • Normal fault on the coast of Somerset, England
  • Reverse fault in the Grands Causses in Bédarieux, France

  
• A break along rocks or rock layers must have experienced slippage or displacement for it to be classified as a fault. If there is no displacement present in the rocks, the break is termed as a fracture.