Flat are fault surfaces that form parallel to the strata and usually in weak rock units, such as evaporites and shales. Ramps cut across more resistant rock units, for example sandstone and limestone, forming a dip angle that is typically 30 to 45 degrees. Ramp-flat geometry forms in both extensional and compressional environments, deforming stratified material. Ramps can occur in a frontal, oblique or lateral position.
Frontal ramps intersect the main fault perpendicular to the displacement direction of the fault.
Oblique ramps intersect the main fault at an incline to the displacement direction. Lateral ramps have a strike parallel to the displacement direction, and can be considered tear faults . Fault ramps develop due to the amount of stress on the slip surface which will cause the fault to cut up through the more competent layers. This pattern produces anticlinal and synclinal features. The amount of movement along a flat could be 10's of miles and the height of a flat can be 1,000's of feet.