![]() They are the result of shear as one block slides past another (also called parasitic folds).ĭrag fold in fine-grained calcareous and dolomitic lutites (Paleoproterozoic Mavor Formation, Belcher Islands). Oblique versions of these end members have components of dip-slip and strike-slip.ĭrag folds and tension gashes also provide good kinematic indicators of fault displacement. If they are normal to fault plane strike, then slip was either up or down dip if parallel to strike then displacement was strike-slip. Slickenlines are valuable indicators of fault slip. Useful structures on slickensided planes are parallel arrays of striae and grooves, or slickenlines. Polished fault planes are called slickensides. The line connecting the two points gives a measure of net displacement, from which dip-slip displacement can be calculated using simple trigonometric functions. Piercing points are a special kind of cutoff, that refer to the displacement of specific objects of linear structures that can be traced from the foot wall to hanging wall. Fault plane structures such as slickenlines will provide the other component of slip – its direction. Foot wall and hanging wall cutoffs refer to the point where a layer is truncated by the fault plane. The vertical and horizontal components of slip ( throw and heave respectively) are determined by identifying footwall and hanging wall cutoffs of suitable markers – specific beds or rock units that can be traced from the footwall to hanging wall blocks. Any other measures will be components of slip, or apparent slip. An easy way to remember which term applies – the footwall is what you stand on the hanging wall is over your head.Ī true measure of fault block displacement is its slip. This is a landward section of the active accretionary wedge – forearc basin above the Hikurangi Subduction Zone, Waimarama coast, eastern New Zealand.ĭisplaced rocks on either side of a fault are described as footwall and hanging wall blocks, the relative displacement of which are important for fault classification. Multiple thrusts (arrows) in relatively weak sandstone and bentonitic mudstone have reduced the once coherent strata to fault breccia and cataclastite.
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