Sinistral
From Wikipedia, the free encyclopedia
- This article is about the geologic usage, for human physiology usage see the articles left-handed and laterality.
Sinistral or left lateral refers to the horizontal movement of blocks on either side of a geological fault or the sense of movement within a shear.
Movement is sinistral (left handed) if the block on the other side of the fault moves to the left, or if stradling the fault the left side moves toward the observer.
Sinistral gains its origins from the Latin "sinister" for left-handed. The opposite sense of movement dextral gains its name from the Latin "dexter" for right-handed.
Schematic illustration of the two strike-slip fault types. The view is of the Earth's surface as from space.
[edit] Identifying sense of throw
Identifying the sense of throw of a fault or the sense of shear can be achieved via several methods:
- Mappable offset of rock units
- Offset of visible bedding, cross cutting dykes
- Folding of strata proximal to a fault caused by frictional drag
- Shear sense indicators in sheared rocks such as
- Mica fish
- Extensional veins
- Shear deflections and stair-stepping of shear folia
