Slickenside

A slickenside can occur as a single surface at a fault between two hard surfaces. Alternatively, the gouge between the fault surfaces may contain many anastamosing slip surfaces that host slickensides.{{cite book |last1=Scholz |first1=Christopher H. |title=The Mechanics of Earthquakes and Faulting |date=2019 |publisher=Cambridge University Press |isbn=978-1-107-16348-5 |page=128 |url=https://books.google.com/books?id=ynWIDwAAQBAJ&pg=PA128 }} These slip surfaces are on the order of 100 micrometers thick,{{cite journal |last1=Sagy |first1=Amir |last2=Brodsky |first2=Emily E. |title=Geometric and rheological asperities in an exposed fault zone |journal=Journal of Geophysical Research: Solid Earth |date=February 2009 |volume=114 |issue=B2 |doi=10.1029/2008JB005701 |bibcode=2009JGRB..114.2301S }} and the size of the grains that constitute the surface are ultra-fine (0.01–1 micrometers in diameter).{{cite journal |last1=Power |first1=William L. |last2=Tullis |first2=Terry E. |title=The relationship between slickenside surfaces in fine-grained quartz and the seismic cycle |journal=Journal of Structural Geology |date=January 1989 |volume=11 |issue=7 |pages=879–893 |doi=10.1016/0191-8141(89)90105-3 |bibcode=1989JSG....11..879P }} These grains are unlike typical grains of fault rock in that they have irregular grain boundaries and few crystal lattice defects (termed dislocations).

Slickensides have conspicuous shapes that can be used to determine the direction of movement along the fault.{{cite journal |last1=Doblas |first1=Miguel |title=Slickenside kinematic indicators |journal=Tectonophysics |date=September 1998 |volume=295 |issue=1–2 |pages=187–197 |doi=10.1016/S0040-1951(98)00120-6 |bibcode=1998Tectp.295..187D }} Straight slickenlines indicate linear-translational fault motion. They are parallel to the direction of fault motion and serve as a kinematic indicator.{{cite journal |last1=Mandal |first1=Nibir |last2=Chakraborty |first2=Chandan |title=Fault motion and curved slickenlines: A theoretical analysis |journal=Journal of Structural Geology |date=January 1989 |volume=11 |issue=4 |pages=497–501 |doi=10.1016/0191-8141(89)90026-6 |bibcode=1989JSG....11..497M }} Curved slickenlines have recently been studied for their potential to preserve the direction of earthquake rupture propagation.{{cite journal |last1=Kearse |first1=Jesse |last2=Kaneko |first2=Yoshihiro |last3=Little |first3=Tim |last4=Van Dissen |first4=Russ |title=Curved slickenlines preserve direction of rupture propagation |journal=Geology |date=September 2019 |volume=47 |issue=9 |pages=838–842 |doi=10.1130/G46563.1 |bibcode=2019Geo....47..838K }}

Slickenside formation results in unique roughness on a slip surface. Fault surface roughness (or topography) is characterized by the aspect ratio of asperity height to scale of observation, and this roughness is a key parameter in the study of fault slip.{{cite journal |last1=Brodsky |first1=Emily E. |last2=Kirkpatrick |first2=James D. |last3=Candela |first3=Thibault |title=Constraints from fault roughness on the scale-dependent strength of rocks |journal=Geology |date=January 2016 |volume=44 |issue=1 |pages=19–22 |doi=10.1130/G37206.1 |bibcode=2016Geo....44...19B |doi-access=free }} In general, a fault surface appears rougher at smaller scales (i.e., rough and bumpy at approximately millimetre scales and smaller, and increasingly smooth with larger fields of view).{{cite journal |last1=Candela |first1=Thibault |last2=Renard |first2=François |last3=Klinger |first3=Yann |last4=Mair |first4=Karen |last5=Schmittbuhl |first5=Jean |last6=Brodsky |first6=Emily E. |title=Roughness of fault surfaces over nine decades of length scales |journal=Journal of Geophysical Research: Solid Earth |date=August 2012 |volume=117 |issue=B8 |doi=10.1029/2011JB009041 |bibcode=2012JGRB..117.8409C }} This smoothing with larger observation scales is more pronounced in the slip-parallel direction than the slip-perpendicular direction and is commonly a result of slickenside formation.

File:Fairview Fault mirror at Dixie Valley Nevada.jpg

The unique geometry of a slickenside can be created in a variety of ways, but the precise mechanisms that create them is not well understood. The grinding between two rocks produces granular material, and there is a change in the behaviour of wear material when the particle size is reduced to nanometers.{{cite journal |last1=Toy |first1=Virginia G. |last2=Niemeijer |first2=André |last3=Renard |first3=Francois |last4=Morales |first4=Luiz |last5=Wirth |first5=Richard |title=Striation and slickenline development on quartz fault surfaces at crustal conditions: Origin and effect on friction |journal=Journal of Geophysical Research: Solid Earth |date=May 2017 |volume=122 |issue=5 |pages=3497–3512 |doi=10.1002/2016JB013498 |bibcode=2017JGRB..122.3497T |hdl=1874/351354 |hdl-access=free }} When the particle size is reduced so dramatically that the surface becomes shiny, it can be characterized as a fault mirror.

A fault mirror may also be the result of fluid being present at the fault surface during slip.{{cite journal |last1=Kirkpatrick |first1=J.D. |last2=Rowe |first2=C.D. |last3=White |first3=J.C. |last4=Brodsky |first4=E.E. |title=Silica gel formation during fault slip: Evidence from the rock record |journal=Geology |date=September 2013 |volume=41 |issue=9 |pages=1015–1018 |doi=10.1130/G34483.1 |bibcode=2013Geo....41.1015K }} Once slip has stopped, this fluid solidifies as a silica gel, which appears shiny and hosts slickenlines.

An asperity on a fault surface is a bump or point with higher relief than the area around it. The asperity, when pressed into the opposing rock surface and then moved, digs into the opposing rock, forming troughs, grooves, and scratches.{{cite journal |last1=Means |first1=W.D. |title=A newly recognized type of slickenside striation |journal=Journal of Structural Geology |date=1987 |volume=9 |issue=5–6 |pages=585–590 |doi=10.1016/0191-8141(87)90143-X |bibcode=1987JSG.....9..585M }} Asperity plowing is thus a result of permanent deformation in the brittle regime at a small scale.{{cite journal |last1=Kirkpatrick |first1=James D. |last2=Brodsky |first2=Emily E. |title=Slickenline orientations as a record of fault rock rheology |journal=Earth and Planetary Science Letters |date=December 2014 |volume=408 |pages=24–34 |doi=10.1016/j.epsl.2014.09.040 |bibcode=2014E&PSL.408...24K |doi-access=free }}

When an asperity plows into the opposing rock, it wears itself and the opposing rock down and produces fine debris. This debris, or wear product, accumulates both in front of and behind the asperity in a long, elongated shape. If the asperity is relatively hard, the debris will accumulate in front of the asperity. If the asperity is relatively soft, the debris will trail behind. This debris hardens over time and is preserved as a form of slickenline.

Some rocks may contain particles that are harder than the rest of the rock. When these rocks are worn, the harder particles will resist wear more than the softer rock, the rock on the lee side of the hard particle will be protected from wear. This creates a tail that starts abruptly as a crag where the hard particle was located and is elongated parallel to the direction of movement down-slip from the particle.

File:Slicks.png

The fault plane may be coated by mineral fibres that grew in during the fault movement, known as slickenfibres. Due to irregularities in the fault plane, exposed slickenfibres typically have a stepped appearance that can be used to determine the sense of movement across the fault.

File:Calcite-chlorite slickenfibres on a small fault slickenside.jpg

Slickenfibres are secondary minerals that make up the slickensides rather than the rock itself. Slickenfibres form in areas where the rock slowly creep past one another rather than sliding suddenly as a result of an earthquake.{{cite journal |last1=Ishii |first1=Eiichi |title=Estimation of the highest potential transmissivity of discrete shear fractures using the ductility index |journal=International Journal of Rock Mechanics and Mining Sciences |date=December 2017 |volume=100 |pages=10–22 |doi=10.1016/j.ijrmms.2017.10.017 |bibcode=2017IJRMM.100...10I }} Unlike slickenlines, which give two possibilities for slip direction, slickenfibres preserve the true slip direction.

Slickensides provide useful insight into earthquake processes. Calcite slickenfibres have recently been used to constrain the depth of aseismic creep in the Zagros Mountains as well as the orientation of stress acting on the fault.{{cite journal |last1=Sarkarinejad |first1=Khalil |last2=Mottahedi |first2=Maryam |last3=Nori |first3=Maryam |title=Aseismic slip on the active Sabz-Pushan and Sepidar thrusts, Iran: microstructural and kinematics evidence of the slickenline fibre creep |journal=International Journal of Earth Sciences |date=November 2021 |volume=110 |issue=8 |pages=2831–2848 |doi=10.1007/s00531-021-02081-1 |bibcode=2021IJEaS.110.2831S }} It has also been suggested that when multiple slickenfibre or slickensteps orientations are present, it can indicate that the ongoing shear is not strain softening so slip does not have a constant direction.

In addition to the direction of slip, slickenlines have also been used to constrain the timing of fault slip.{{cite journal |last1=Norris |first1=D.K. |title=Slickenlines and the kinematics of the Crowsnest Deflection in the southern Rocky Mountains of Canada |journal=Journal of Structural Geology |date=June 2001 |volume=23 |issue=6–7 |pages=1089–1102 |doi=10.1016/S0191-8141(00)00180-2 |bibcode=2001JSG....23.1089N }} They also preserve any complexity in the geometry of the earthquake rupture.{{cite journal |last1=Macklin |first1=Clarrie |last2=Kaneko |first2=Yoshihiro |last3=Kearse |first3=Jesse |title=Coseismic slickenlines record the emergence of multiple rupture fronts during a surface-breaking earthquake |journal=Tectonophysics |date=June 2021 |volume=808 |pages=228834 |doi=10.1016/j.tecto.2021.228834 |bibcode=2021Tectp.80828834M }}

In pedology, the study of soils in their natural environments, a slickenside is a surface of the cracks produced in soils containing a high proportion of swelling clays. Slickensides are a type of cutan.

In the Australian Soil Classification, slickensides, along with lenticular structural aggregates, are an indicator of a vertisol.{{cite book |last1=Isbell |first1=R. F. |title=The Australian Soil Classification |date=1996 |publisher=CSIRO Australia |isbn=978-0-643-05813-2 }}{{pn|date=March 2024}}

On the Moon, a boulder with slickensides, discovered in a debris-strewn small crater at Station 9 near Rima Hadley, was photographed during a moonwalk by the crew of Apollo 15.https://www.lpi.usra.edu/resources/apollo/catalog/70mm/magazine/?82 Apollo Image Atlas (Lunar and Planetary Institute), 70 mm Hasselblad Image Catalog, Apollo 15 photographs AS15-82-11101, AS15-82-11102, AS15-82-11103 and AS15-82-11104https://www.hq.nasa.gov/alsj/a15/a15.sta9.html Apollo 15 Lunar Surface Journal – Instant Rock at Station 9https://history.nasa.gov/alsj/a15/A15SampleCat_1.pdf Catalog of Apollo 15 Rocks – Part 1. 15015-15299

File:FaultLineScarp.JPG|An exposed reverse fault plane with large slickenlines. Gobi, Mongolia.

File:PySlick.JPG|Dextral slickenside of pyrite

File:Slickensides.JPG|Slickensides developed on the surface of a small fault in quartzite in the Alpujarras

Image:Bear Valley Slickensides.jpg|Slickensides on a fault plane, south wall of Bear Valley Strip Mine. Lens cap 5.8cm wide.

File:East Kilve slickenfibres.JPG|Calcite slickenfibres on the surface of a normal fault, east of Kilve, Somerset.

File:Slickenside - Corona Heights, San Francisco.jpg|Slickensides on a fault plane in Corona Heights Park, San Francisco

{{reflist}}

• {{cite book |chapter-url=https://www.oxfordreference.com/view/10.1093/acref/9780199211944.001.0001/acref-9780199211944-e-7762 |isbn=978-0-19-921194-4 |title=A Dictionary of Earth Sciences |chapter=Slickenside |date=2008 |publisher=Oxford University Press |editor1-first=Michael |editor1-last=Allaby }}
• {{cite book |last1=McDonald |first1=Ronald C. |title=Australian Soil and Land Survey: Field Handbook |date=1998 |publisher=CSIRO |isbn=978-0-643-06356-3 }}
• {{cite book |last1=Passchier |first1=Cees W. |last2=Trouw |first2=Rudolph A. J. |title=Microtectonics |date=2005 |publisher=Springer Science & Business Media |isbn=978-3-540-64003-5 |doi=10.1007/3-540-29359-0 }}

• {{Cite Americana|wstitle=Slickensides|year=1920|short=x}}

{{Structural geology}}

Category:Pedology

Category:Structural geology