cause local damming of drainage systems, resulting in ponding and establishment of local base level (b) Fault-sag ponding: fault zones commonly form low-lying zones via differential erosion, may form sites of elongated ponds, and linear series of ponds along length of fault zone (3) Spring Development (a) Linear, aligned springs commonly form along fault zone (4) Surface Uplift/Marine Terracing (a) Erosion Surfaces i) Wave-cut terraces and stream terraces may become displaced by fault offset ii) Uplift of land surface results in elevating the erosional surface above active level of erosion 3. Block Fault Topography: essentially fault-bounded mountains and
56 lowlands of the Basin and Range Province a. Fault-Block Mountains: fault bounded uplift along mountain fronts, alternating with fault-bounded down-dropping of structural basins b. Horst and Grabens (1) Horsts: Uplifted fault blocks (2) Grabens: Down-dropped fault blocks (a) Half-grabens: asymmetric faulting on one side of graben (b) Tilted Fault-block Mountains: asymmetric faulting on one side of mountain block c. Strike-slip Faults: primary sense of displacement is horizontal, along strike of fault plane (e.g. San Andreas Transform Zone) (1) Recognition (a) Offset Streams (b) Sag Ponds (c) Mismatched topography/bedrock with intervening lineament d. Thrust Faults: low-angle reverse faults, (1) Klippes: erosional remnants of Upper Thrust Sheet, stranded and surrounded by rocks of lower thrust sheet (a) base of klippe marks location of thrust fault (b) e.g. Chief Mountain, Montana (2) Fensters: erosional windows cut through Upper Thrust Sheet, showing rocks of lower thrust sheet surrounded by rocks of upper thrust sheet. III. Determination of Fault Displacement A. Defining Factors of Displacement 1. Magnitude of Displacement: how much shear motion along fault 2. Direction of Displacement a. Magnitude + Direction = "vector" in physics
57 B. Complete Determination of Displacement 1. Process: I.D. pre=existing linear feature that has been cut and offset by fault plane a. Piercing points: points of intersection between linear feature and fault plane (1) I.D. Offset piercing points (a) vector connecting two piercing points = direction and magnitude of fault displacement b. Linear features of Use (1) two other faults that form a line of intersection (2) intersecting dikes/veins (3) hinge line of a fold C. Partial Determination of Displacement 1. Slickenlines 2. Pinnate fractures 3. drag folds 4. en echelon gash fractures 5.