What Forces Created These Geologic Features?
ES1106  Interpreting a Fault

The image below shows a fault. Follow these steps to interpret the forces that caused it:

  • Look for at least one rock layer that appears on both sides of the image.
  • Identify the line or zone where that layer is cut. This is the fault.
  • Examine the orientation of the fault. Decide which rocks are below and above the fault. The side below the fault is the footwall. The side above the fault is the hanging wall.
  • Examine how the layer you identified has been offset. If the hanging wall moved down relative to the footwall, the movement was caused by tension. If the hanging wall moved up relative to the footwall, the movement was caused by compression.
  • Tension (stretching) causes normal faults. Compression (pushing together) causes reverse faults.
  !   Click the buttons along the bottom of the image to see an example of interpreting a fault.
Normal Fault, Whipple Mountains, Arizona

1. Sketch the fault including layers A and B. Label the fault, hanging wall, and footwall. Name the type of fault, and draw arrows to indicate the direction of stress.

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