Faulting Geometry: Faulting is a intricate process, and there’s a wide range of faults with various characteristics. To simplify and categorize these faults, we use three key measurements that describe their geometry: dip, strike, and slip.
Dip
- Faults on Earth come in different orientations, ranging from vertical to horizontal.
- The orientation is described by the dip angle, which indicates how steep the fault surface is.
- This angle is measured from the Earth’s surface or a plane parallel to it.
- Dip is the measure of the steepness of a fault surface.
- A horizontal fault has a dip of 0°, and a vertical fault has a dip of 90°.
- Imagine you’re tunneling through a fault.
- The rock above your head is called the hanging wall, and the rock beneath your feet is called the footwall.
- So, if you were walking through the tunnel, the hanging wall would be above you, and the footwall would be below.
Strike
- The strike is the angle telling you which way a fault runs, measured clockwise.
- A strike of 0° or 180° means the fault is north-south.
- A strike of 90° or 270° means it’s east-west.
- Always describe the strike so that if you face in that direction, the fault dips to your right.
- If it’s a straight-up-and-down fault, mention it as a special case.
- If a fault curves, the strike changes along its length, but it’s usually not a problem if you specify the location (like latitude and longitude) of the measurement.
Slip
- Think of the fault orientation as the “tilt” and “direction” of the fault.
- Dip describes how the fault slopes underground, like the angle of a ramp.
- Strike is like a compass direction on the Earth’s surface, indicating the horizontal orientation of the fault.
- Slip: Slip is how much and in what direction one side of the fault moved compared to the other.
- Magnitude of slip tells us how far the rocks shifted, usually in centimeters for small quakes and meters for larger ones.
- Direction of slip is a vector, like a compass heading on the fault surface.Components of Slip
- Magnitude: Describes the distance the two sides of the fault moved. Small quakes may have a magnitude in centimeters, while larger events could be measured in meters.
- Direction: Indicates how the hanging wall moved relative to the footwall. Measured as an angle on the fault surface.
- If the hanging wall moves right, the slip direction is 0°.If it moves up, the slip angle is 90°.
- Leftward movement corresponds to a slip angle of 180°.
- Downward movement is represented by a slip angle of 270° or -90°.
Read Also: What Are Faults?
