Fault Facts



  • A fault is a rock fracture where blocks of rock have slipped past each other.
  • Faults usually occur in fault zones, which are often along the boundaries between tectonic plates. Faults are typically caused by earthquakes.
  • Single earthquakes rarely move blocks more than a few centimeters. Repeated small earthquakes can shift blocks hundreds of kilometers.
  • Compression faults are faults caused by rocks being squeezed together, perhaps by converging plates.
  • Tension faults are faults caused by rocks being pulled together, perhaps by diverging plates.
  • Normal, or dip-slip, faults are tension faults where the rock fractures and slips straight down.
  • A wrench, or tear, fault occurs when plates slide past each other and make blocks slip horizontally.
  • Large wrench faults, such as the San Andreas in California, USA, are called transcurrent faults.
  • Rift valleys are huge, trough-shaped valleys created by faulting, such as Africa’s Great Rift Valley. The floor is a thrown-down block called a graben. Some geologists think they are caused by tension, others by compression.
  • Horst blocks are blocks of rock thrown up between normal faults, often creating a high plateau