Strike-slip tectonics

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Strike-slip tectonics or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust (and lithosphere). Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, this is known as a transform or conservative plate boundary. Areas of strike-slip tectonics are characterised by particular deformation styles including: stepovers, Riedel shears, flower structures and strike-slip duplexes. Where the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either transpressional or transtensional 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 zones of continental collision. [1] [2]

Contents

Deformation styles

Development of Riedel shears in a zone of dextral shear Riedel.jpg
Development of Riedel shears in a zone of dextral shear
Flower structures developed along minor restraining and releasing bends on a dextral (right-lateral) strike-slip fault Flowerstructure1.png
Flower structures developed along minor restraining and releasing bends on a dextral (right-lateral) strike-slip fault

Stepovers

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 km, or possibly more are feasible. This is backed up by evidence that the rupture of the 2001 Kunlun earthquake jumped more than 10 km across an extensional stepover. [3] The presence of stepovers during the rupture of strike-slip fault zones has been associated with the initiation of supershear propagation (propagation in excess of the S-wave velocity) during earthquake rupture. [4]

Riedel shear structures

In the early stages of strike-slip fault formation, displacement within basement rocks produces characteristic fault structures within the overlying cover. This will also be the case where an active strike-slip zone lies within an area of continuing sedimentation. At low levels of strain, the overall simple shear causes a set of small faults to form. The dominant set, known as R shears, forms at about 15° to the underlying fault with the same shear sense. The R shears are then linked by a second set, the R' shears, that forms at about 75° to the main fault trace. [5] These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. With further displacement, the Riedel fault segments will tend to become fully linked until a throughgoing fault is formed. The linkage often occurs with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears relative to the overall shear direction. [6] The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry. [7]

Flower structures

In detail, many strike-slip faults at surface consist of en echelon 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 transpressional (i.e. with a small component of shortening) or transtensional (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. [8]

An exposure of highy deformed bedded chert in Busuanga, Philippines, containing a flower structure (yellow dashed lines) Deformed bedded chert with flower structures, Busuanga, Palawan (annotated).png
An exposure of highy deformed bedded chert in Busuanga, Philippines, containing a flower structure (yellow dashed lines)

Strike-slip duplexes

Strike-slip duplexes occur at the stepover regions of faults, forming lens-shaped near parallel arrays of horses. These occur between two or more large bounding faults which usually have large displacements. [9]

An idealized strike-slip fault runs in a straight line with a vertical dip and has only horizontal motion, thus there is no change in topography due to motion of the fault. In reality, as strike-slip faults become large and developed, their behavior changes and becomes more complex. A long strike-slip fault follows a staircase-like trajectory consisting of interspaced fault planes that follow the main fault direction. [10] These sub-parallel stretches are isolated by offsets at first, but over long periods of time, they can become connected by stepovers to accommodate the strike-slip displacement. [9] In long stretches of strike-slip, the fault plane can start to curve, giving rise to structures similar to step overs. [11]

Right lateral motion of a strike-slip fault at a right stepover (or overstep) gives rise to extensional bends characterised by zones of subsidence, local normal faults, and pull-apart basins. [9] 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 stepovers which are displayed by local reverse faults, push-up zones, and folds. [11] On contractional duplex structures, thrust faults will accommodate vertical displacement rather than being folded, as the uplifting process is more energy-efficient. [11]

Strike-slip duplexes are passive structures; they form as a response to displacement of the bounding fault rather than by the stresses from plate motion. [10] Each horse has a length that varies from half to twice the spacing between the bounding fault planes. Depending on the properties of the rocks and the fault, the duplexes will have different length ratios and will develop on either major or subtle offsets, although it is possible to observe duplex structures that develop on nearly straight fault segments. [11] Because the motion of the duplexes may be heterogeneous, the individual horses can experience a rotation with a horizontal axis, which results in the formation of scissor faults. Scissor faults exhibit normal motion at one end of the horse and a thrust motion at the other end. [11] Because strike-slip duplexes structures have more horizontal motion than vertical motion, they are best observed on a map rather than a vertical projection and are a good indication that the main fault has a strike-slip motion. [9]

An example of strike-slip duplexes is observed in the Lambertville sill, New Jersey. [12] Flemington and the Hopewell faults, the two main faults in the region, experienced 3 km of dip-slip and over 20 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. [12] 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. [12]

Geological environments associated with strike-slip tectonics

San Andreas Transform Fault on the Carrizo Plain Aerial-SanAndreas-CarrizoPlain.jpg
San Andreas Transform Fault on the Carrizo Plain

Areas of strike-slip tectonics are associated with:

Oceanic transform boundaries

Mid-ocean ridges are broken into segments offset from each other by transform faults. The active part of the transform links the two ridge segments. Some of these transforms can be very large, such as the Romanche fracture zone, whose active portion extends for about 300 km.

Continental transform boundaries

Transform faults within continental plates include some of the best-known examples of strike-slip structures, such as the San Andreas Fault, the Dead Sea Transform, the North Anatolian Fault and the Alpine Fault.

Lateral ramps in areas of extensional or contractional tectonics

Major lateral offsets between large extensional or thrust faults are normally connected by diffuse or discrete zones of strike-slip deformation allowing the transfer of the overall displacement between the structures.

Zones of oblique collision

In most zones of 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 accommodating all the strike-slip component along the boundary. Examples include the Main Recent Fault along the boundary between the Arabian Plate and Eurasian Plate behind the Zagros fold and thrust belt, [13] the Liquiñe-Ofqui Fault that runs through Chile and the Great Sumatran fault that runs parallel to the subduction zone along the Sunda Trench.

The deforming foreland of a zone of continent-continent collision

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 Plate as it responds to collision with the Indian Plate, such as the Kunlun fault and Altyn Tagh fault. [14]

Related Research Articles

<span class="mw-page-title-main">Transform fault</span> Plate boundary where the motion is predominantly horizontal

A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone. A transform fault is a special case of a strike-slip fault that also forms a plate boundary.

<span class="mw-page-title-main">Fault (geology)</span> Fracture or discontinuity in displaced rock

In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Faults may also displace slowly, by aseismic creep.

<span class="mw-page-title-main">Tectonics</span> Process of evolution of the Earths crust

Tectonics are the processes that result in the structure and properties of the Earth's crust and its evolution through time.

<span class="mw-page-title-main">Shear (geology)</span> Response of rock to deformation

In geology, shear is the response of a rock to deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics.

<span class="mw-page-title-main">Transpression</span> Type of strike-slip deformation

In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. It is generally very unlikely that a deforming body will experience "pure" shortening or "pure" strike-slip. The relative amounts of shortening and strike-slip can be expressed in the convergence angle alpha which ranges from zero to 90 degrees. During shortening, unless material is lost, transpression produces vertical thickening in the crust. Transpression that occurs on a regional scale along plate boundaries is characterized by oblique convergence. More locally, transpression occurs within restraining bends in strike-slip fault zones.

<span class="mw-page-title-main">Fault trace</span> Intersection of a geological fault with the Earths surface

A fault trace describes the intersection of a geological fault with the Earth's surface, which leaves a visible disturbance on the surface, usually looking like a crack in the surface with jagged rock structures protruding outward. The term also applies to a line plotted on a geological map to represent a fault. These fractures tend to occur when a slip surface expands from a fault core, especially during an earthquake. This tends to occur with fault displacement, in which surfaces on both sides of a fault, known as fault blocks, separate horizontally or vertically.

<span class="mw-page-title-main">Queen Charlotte Fault</span> Active transform fault in Canada and Alaska

The Queen Charlotte Fault is an active transform fault that marks the boundary of the North American plate and the Pacific plate. It is Canada's right-lateral strike-slip equivalent to the San Andreas Fault to the south in California. The Queen Charlotte Fault forms a triple junction south with the Cascadia subduction zone and the Explorer Ridge. The Queen Charlotte Fault (QCF) forms a transpressional plate boundary, and is as active as other major transform fault systems in terms of slip rates and seismogenic potential. It sustains the highest known deformation rates among continental or continent-ocean transform systems globally, accommodating greater than 50mm/yr dextral offset. The entire approximately 900 km offshore length has ruptured in seven greater than magnitude 7 events during the last century, making the cumulative historical seismic moment release higher than any other modern transform plate boundary system.

<span class="mw-page-title-main">Dead Sea Transform</span> Fault system between the African and Arabian plates

The Dead Sea Transform (DST) fault system, also sometimes referred to as the Dead Sea Rift, is a series of faults that run for about 1,000 km from the Maras Triple Junction to the northern end of the Red Sea Rift. The fault system forms the transform boundary between the African Plate to the west and the Arabian Plate to the east. It is a zone of left lateral (sinistral) displacement, signifying the relative motions of the two plates. Both plates are moving in a general north-northeast direction, but the Arabian Plate is moving faster, resulting in the observed left lateral motions along the fault of approximately 107 km at its southern end. A component of extension is also present in the southern part of the transform, which has contributed to a series of depressions, or pull-apart basins, forming the Gulf of Aqaba, Dead Sea, Sea of Galilee, and Hula basins. A component of shortening affects the Lebanon restraining bend, leading to uplift on both sides of the Beqaa valley. There is local transtension in the northernmost part of the fault system, forming the Ghab pull-apart basin. The southern part of the fault system runs roughly along the political border of Lebanon and Israel on its western side, and southern Syria and Jordan on the eastern side.

<span class="mw-page-title-main">East Anatolian Fault</span> Fault line between the Anatolian Plate and the northward-moving Arabian Plate

The East Anatolian Fault is a ~700 km long major strike-slip fault zone running from eastern to south-central Turkey. It forms the transform type tectonic boundary between the Anatolian sub-plate and the northward-moving Arabian Plate. The difference in the relative motions of the two plates is manifest in the left lateral motion along the fault. The East and North Anatolian faults together accommodate the westward motion of the Anatolian sub-plate as it is squeezed out by the ongoing collision between the Arabian Plate and the Eurasian Plate.

<span class="mw-page-title-main">2001 Kunlun earthquake</span> 2001 earthquake in western China

An earthquake occurred in China on 14 November 2001 at 09:26 UTC, with an epicenter near Kokoxili, close to the border between Qinghai and Xinjiang in a remote mountainous region. With a magnitude of 7.8 Mw, it was the most powerful earthquake in China for 5 decades. No casualties were reported, presumably due to the very low population density and the lack of high-rise buildings. This earthquake was associated with the longest surface rupture ever recorded on land, ~450 km.

<span class="mw-page-title-main">1911 Kebin earthquake</span> Earthquake in Kazakhstan on 3 January 1911

The 1911 Kebin earthquake, or Chon-Kemin earthquake, struck Russian Turkestan on 3 January. Registering at a moment magnitude of 8.0, it killed 452 people, destroyed more than 770 buildings in Almaty, Kazakhstan, and resulted in 125 miles (201 km) of surface faulting in the valleys of Chon-Kemin, Chilik and Chon-Aksu.

<span class="mw-page-title-main">Marlborough fault system</span> Active fault system in New Zealand

The Marlborough fault system is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island, New Zealand, which transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary of the Kermadec Trench, and together form the boundary between the Australian and Pacific Plates.

The 1932 Changma earthquake occurred at 10:04:27 local time on 25 December. With an estimated magnitude of 7.6 on the surface wave magnitude scale, and a maximum felt intensity of X (Extreme) on the Mercalli intensity scale, the quake destroyed 1,167 houses and caused 275 to 70,000 deaths and 320 injuries.

<span class="mw-page-title-main">El Tigre Fault</span>

The El Tigre Fault is a 120 km long, roughly north-south trending, major strike-slip fault located in the Western Precordillera in Argentina. The Precordillera lies just to the east of the Andes mountain range in South America. The northern boundary of the fault is the Jáchal River and its southern boundary is the San Juan River. The fault is divided into three sections based on fault trace geometry, Northern extending between 41–46 km in length, Central extending between 48–53 km in length, and Southern extending 26 km in length. The fault displays a right-lateral (horizontal) motion and has formed in response to stresses from the Nazca Plate subducting under the South American Plate. It is a major fault with crustal significance. The Andes Mountain belt trends with respect to the Nazca Plate/South American Plate convergence zone, and deformation is divided between the Precordilleran thrust faults and the El Tigre strike-slip motion. The El Tigre Fault is currently seismically active.

<span class="mw-page-title-main">Leaky transform fault</span> Transform fault producing new crust

A leaky transform fault is a transform fault with volcanic activity along a significant portion of its length producing new crust. In addition to the regular strike-slip motion observed at transform boundaries, an oblique extensional component is present, resulting in motion of the plates that is not parallel to the plate boundary. This opens the fault, allowing melt to break through and cool on the ocean floor, producing new crust. This extensional component can come from a slight shift in the position of a plate's Euler Pole. In order to accommodate oblique motion along the plate boundary, these leaky transform faults can break up into a series of small transforms linked by short segments of spreading ridges. These new transforms will follow small circles centred on the new Euler Pole.

On July 17, 2017, an earthquake struck near the Komandorski Islands, east of the Kamchatka Peninsula in the Bering Sea at. Although there were no casualties from this earthquake, it was notable for a rare characteristic known as supershear, and is one of the few times a large supershear earthquake has been observed. It was preceded by a few foreshocks months earlier, and aftershocks that continued for nearly six months.

<span class="mw-page-title-main">Oblique subduction</span> Tectonic process

Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.

The 1850 Xichang earthquake rocked Sichuan Province of Qing China on September 12. The earthquake which caused major damage in Xichang county had an estimated moment magnitude of 7.3–7.9 Mw  and a surface wave magnitude of 7.5–7.7 Ms . An estimated 20,650 people died.

The 1997 Bojnurd earthquake occurred on 4 February at 14:07 IRST in Iran. The epicenter of the Mw 6.5 earthquake was in the Kopet Dag mountains of North Khorasan, near the Iran–Turkmenistan border, about 579 km (360 mi) northeast of Tehran. The earthquake is characterized by shallow strike-slip faulting in a zone of active faults. Seismic activity is present as the Kopet Dag is actively accommodating tectonics through faulting. The earthquake left 88 dead, 1,948 injured, and affected 173 villages, including four which were destroyed. Damage also occurred in Shirvan and Bojnord counties. The total cost of damage was estimated to be over US$ 30 million.

Magmatism along strike-slip faults is the process of rock melting, magma ascent and emplacement, associated with the tectonics and geometry of various strike-slip settings, most commonly occurring along transform boundaries at mid-ocean ridge spreading centres and at strike-slip systems parallel to oblique subduction zones. Strike-slip faults have a direct effect on magmatism. They can either induce magmatism, act as a conduit to magmatism and magmatic flow, or block magmatic flow. In contrast, magmatism can also directly impact on strike-slip faults by determining fault formation, propagation and slip. Both magma and strike-slip faults coexist and affect one another.

References

  1. ↑ Acocella, V. (2021). Volcano-Tectonic Processes. Springer International Publishing. p. 74. ISBN   9783030659684.
  2. ↑ Burg, J.-P. (2017). "Strike-slip and Oblique-slip tectonics" (PDF). Retrieved 26 September 2022.
  3. ↑ Zabci, C.; Akyüz, H. S.; Karabacak, V.; Sançar, T.; Altunel, E.; Gürsoy, H.; Tatar, O. (2011). "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". Turkish Journal of Earth Sciences. 20: 411–427.
  4. ↑ Feng, H.; Jiankuan, X.; Zhenguo, Z.; Xiaofei, C. (2016). "Supershear transition mechanism induced by step over geometry". Journal of Geophysical Research: Solid Earth. 121 (12): 8738–8749. doi:10.1002/2016JB013333. S2CID   133444922.
  5. ↑ Katz, Y.; Weinberger R.; Aydin A. (2004). "Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah" (PDF). Journal of Structural Geology. 26 (3): 491–501. Bibcode:2004JSG....26..491K. doi:10.1016/j.jsg.2003.08.003 . Retrieved 6 May 2011.[ permanent dead link ]
  6. ↑ Tchalenko, J.S. (1970). "Similarities between Shear Zones of Different Magnitudes". Geological Society of America Bulletin. 81 (6): 1625–1640. Bibcode:1970GSAB...81.1625T. doi:10.1130/0016-7606(1970)81[1625:SBSZOD]2.0.CO;2.
  7. ↑ Ueta, K.; Tani, K. 2001. Ground Surface Deformation in Unconsolidated Sediments Caused by Bedrock Fault Movements: Dip-Slip and Strike-Slip Fault Model Test and Field Survey. American Geophysical Union, Fall Meeting 2001, abstract #S52D-0682
  8. ↑ Harding, T. P. 1990. Bulletin American Association of Petroleum Geologists. 74
  9. 1 2 3 4 Keary, P. (2009), Global Tectonics, vol. 3, John Wiley & Sons, ISBN   978-1-118-68808-3
  10. 1 2 Woodcock, Nigel (1986), "Strike-slip duplexes", Journal of Structural Geology, 8 (7): 725–735, Bibcode:1986JSG.....8..725W, doi:10.1016/0191-8141(86)90021-0
  11. 1 2 3 4 5 Burg (1986), Strike-slip and oblique-slip tectonics (PDF)
  12. 1 2 3 Laney, A. (1996), "Three-dimensional shuffling of horses in a strike-slip duplex: an example from the Lambertville sill, New Jersey", Tectonophysics, 258 (1–4): 53–70, Bibcode:1996Tectp.258...53L, doi:10.1016/0040-1951(95)00173-5
  13. ↑ Talebian, M. Jackson, J. 2004. A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran Geophysical Journal International, 156, pages 506–526
  14. ↑ 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. Archived 2011-06-06 at the Wayback Machine
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