Strike-slip tectonics: Difference between revisions

{{short description|StructureDeformation anddominated processesby associatedhorizontal with zones of lateral displacementmovement in the Earth's crustlithosphere}}

'''Strike-slip tectonics''' isor concerned'''wrench withtectonics''' theis structuresa formedtype by, and theof [[Tectonics|tectonictectonics]] processesthat associatedis withdominated other zones ofby lateral displacement(horizontal) movements within the Earth's [[Crust (geology)|Earth's crust]] or(and [[lithosphere]], such as ''[[transform boundary|transform boundaries]]''). ItWhere isa onezone of thestrike-slip threetectonics mainforms typesthe ofboundary [[platebetween tectonic]] regime (and respectivetwo [[platePlate boundarytectonics|platetectonic boundariesplates]]), thethis othersis beingknown [[extensionalas tectonics]]a ([[divergenttransform boundaryfault|transform]]) andor [[thrustconservative tectonics]] ([[convergentplate boundary]]). Areas of strike-slip tectonics are associatedcharacterised withby particular deformation styles including: ''stepovers'', ''Riedel shears'', ''flower structures'' and ''strike-slip duplexes''. This typeWhere the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either [[transpression]]al or [[transtension]]al depending on the sense of deviation. Strike-slip tectonics is characteristic of several geological environments, including oceanic and continental transform faults, zones of oblique collision and the deforming foreland of a zonezones of [[continental collision]].<ref>{{Cite book |last=Acocella |first=V. |title=Volcano-Tectonic Processes |publisher=Springer International Publishing |year=2021 |isbn=9783030659684 |pages=74}}</ref><ref name="Burg_2017">{{Cite web |last=Burg |first=J.-P. |date=2017 |title=Strike-slip and Oblique-slip tectonics |url=https://www.files.ethz.ch/structuralgeology/jpb/files/english/5wrench.pdf |access-date=26 September 2022}}</ref>

When strike-slip fault zones develop, they typically form as several separate fault segments that are offset from each other. The areas between the ends of adjacent segments are known as ''stepovers''. In the case of a dextral fault zone, a right-stepping offset is known as an extensional stepover as movement on the two segments leads to extensional deformation in the zone of offset, while a left-stepping offset is known as a compressional stepover. For active strike-slip systems, earthquake ruptures may jump from one segment to another across the intervening stepover, if the offset is not too great. Numerical modelling has suggested that jumps of at least 8 &nbsp;km, or possibly more are feasible. This is backed up by evidence that the rupture of the [[2001 Kunlun earthquake]] jumped more than 10 &nbsp;km across an extensional stepover.<ref name="Zabci_etal_2011">{{Cite journal |last1=Zabci |first1=C. |last2=Akyüz |first2=H. S. |last3=Karabacak |first3=V. |last4=Sançar |first4=T. |last5=Altunel |first5=E. |last6=Gürsoy |first6=H. |last7=Tatar |first7=O. |year=2011 |title=Palaeoearthquakes on the Kelkit Valley Segment of the North Anatolian Fault, Turkey: Implications for the Surface Rupture of the Historical 17 August 1668 Anatolian Earthquake |url=https://journals.tubitak.gov.tr/earth/vol20/iss4/4/|journal=Turkish Journal of Earth Sciences |volume=20 |pages=411–427}}</ref> The presence of stepovers during the rupture of strike-slip fault zones has been associated with the initiation of [[supershear earthquake|supershear]] propagation (propagation in excess of the [[S- wave]] velocity) during earthquake rupture.<ref name="Feng_etal_2016">{{Cite journal |last1=Feng |first1=H. |last2=Jiankuan |first2=X. |last3=Zhenguo |first3=Z. |last4=Xiaofei |first4=C. |date=2016 |title=Supershear transition mechanism induced by step over geometry |journal=Journal of Geophysical Research: Solid Earth |volume=121 |issue=12 |pages=8738–8749 |doi=10.1002/2016JB013333|s2cid=133444922 }}</ref>

In detail, many strike-slip faults at surface consist of [[en echelon]] and/or braided segments, which in many cases were probably inherited from previously formed Riedel shears. In cross-section, the displacements are dominantly reverse or normal in type depending on whether the overall fault geometry is [[transpression]]al (i.e. with a small component of shortening) or [[transtension]]al (with a small component of extension). As the faults tend to join downwards onto a single strand in basement, the geometry has led to these being termed ''flower structure''. Fault zones with dominantly reverse faulting are known as ''positive flowers'', while those with dominantly normal offsets are known as ''negative flowers''. The identification of such structures, particularly where positive and negative flowers are developed on different segments of the same fault, are regarded as reliable indicators of strike-slip.<ref>[http://search.datapages.com/data/doi/10.1306/0C9B2533-1710-11D7-8645000102C1865D Harding, T. P. 1990. Bulletin American Association of Petroleum Geologists. 74]</ref>

[[Sinistral and dextral|Right lateral]] motion of a strike-slip fault at a right step overstepover (or overstep) gives rise to [[Extensional tectonics|extensional]] bends characterised by zones of [[subsidence]], local [[normal fault]]s, and [[pull-apart basin]]s.<ref name = "D"/> On extensional duplexes, normal faults will accommodate the vertical motion, creating negative relief. Similarly, left stepping at a dextral fault generates contractional bends; this shortens the step oversstepovers which are displayed by local [[Fault (geology)|reverse faults]], push-up zones, and [[Fold (geology)|folds]].<ref name = "C"/> On contractional duplex structures, thrust faults will accommodate vertical displacement rather than being folded, as the uplifting process is more energy-efficient.<ref name = "C"/>

An example of strike-slip duplexes wasis observed in the Lambertville sill, New Jersey.<ref name = "B"/> Flemington and the Hopewell faults, the two main faults in the region, experienced 3&nbsp;km of dip-slip and over 20&nbsp;km of strike-slip motions to accommodate regional extension. It is possible to trace the lensoidal structures which are interpreted as horses that form duplexes.<ref name = "B"/> The lens structures observed in the 3M quarry are 180 meters long and 10 meters wide. The main duplex is 30 m in length and other smaller duplexes are also present.<ref name = "B">{{Citation

[[File:Aerial-SanAndreas-CarrizoPlain.jpg|thumb|160px|San Andreas Transform Fault on the [[Carrizo Plain]]]]

In most zones of [[continental collision|continent-continent collision]], the relative movement of the plates is oblique to the plate boundary itself. The deformation along the boundary is normally partitioned into dip-slip contractional structures in the foreland with a single large strike-slip structure in the [[hinterland (geology)|hinterland]] accommodating all the strike-slip component along the boundary. Examples include the ''Main Recent Fault'' along the boundary between the [[Arabian plate|Arabian]] and Eurasian platesplate behind the [[Zagros]] [[fold and thrust belt]],<ref>Talebian, M. Jackson, J. 2004. [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?db_key=AST&bibcode=2004GeoJI.156..506T&letter=0&classic=YES&defaultprint=YES&whole_paper=YES&page=506&epage=506&send=Send+PDF&filetype=.pdf A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran] [[Geophysical Journal International]], 156, pages 506–526</ref> the [[Liquiñe-Ofqui Fault]] that runs through [[Chile]] and the [[Great Sumatran fault]] that runs parallel to the [[subduction]] zone along the [[Java Trench|Sunda Trench]].

The process sometimes known as [[indenter tectonics]], first elucidated by [[Paul Tapponnier]], occurs during a collisional event where one of the plates deforms internally along a system of strike-slip faults. The best known active example is the system of strike-slip structures observed in the [[Eurasian Plateplate]] as it responds to collision with the [[Indian Plateplate]], such as the [[Kunlun fault]] and [[Altyn Tagh fault]].<ref>[http://www.colorado.edu/GeolSci/faculty/molnarpdf/1979JGR.Tapponnier&M.TienShan.pdf Tapponnier, P. & Molnar, P. 1979. Active faulting and Cenozoic tectonics of the Tien Shan, Mongolia and Baykal regions. Journal Geophysical Research, 84, B7, 3425 – 3459.] {{webarchive|url=https://web.archive.org/web/20110606093349/http://www.colorado.edu/GeolSci/faculty/molnarpdf/1979JGR.Tapponnier%26M.TienShan.pdf |date=2011-06-06 }}</ref>