Unit One - Geological Field Methods
2. Measuring Rock Structures
Vocabulary

Hanging Wall: The block of rock above an inclined fault surface.

Footwall: The block of rock below an inclined fault surface.

Normal Fault: A fault, generally steeply inclined, along which the hanging wall block has moved relatively downward.

Reverse Fault: A fault, generally steeply inclined, along which the hanging wall block has moved relatively upward.

Thrust Fault: A special type of reverse fault with a very low angle fault plane, typically dipping < 15 degrees.

Strike Slip Fault: A fault which has horizontal movement, or movement parallel to the strike of the fault plane.

Axial Plane: An imaginary plane which intersects the crest or trough in such a manner that the limbs or sides of the fold are more or less symmetrically arranged with reference to it.

Anticline: Fold with limbs dipping away from the fold axis.

Syncline: Fold with limbs dipping towards the fold axis.

Symmetrical Fold: A fold in which both limbs dip equally away from the axial plane.

Asymmetrical Fold: A fold in which one limb dips more steeply than the other.

Overturned Fold: A fold in which one limb is tilted beyond vertical, resulting in both limbs dipping the same direction, but not at the same dip angle.

Isoclinal Fold: A fold in which both limbs are approximately parallel.

Recumbent Fold: A fold with a nearly horizontal axial plane, resulting in overturned beds on one or the other limbs.

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