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The principal characterized features of earth’s crust within regional strike-slip zones
Published in Vladimir Litvinenko, Advances in Raw Material Industries for Sustainable Development Goals, 2020
Aleksei Ageev, Aleksei Egorov, Nikita Krikun
Nowadays, the most detail-studied by complex geological and geophysical methods is the San Andreas faults system. This tectonic zone is considered as the boundary between the North American craton and the Pacific lithospheric plate. Scientists attribute its foundation to a change in the geodynamic situation on the western edge of the North American continent from subduction to transform, which occurred in the Paleogene (Armstrong, Ward, 1991; Humphreys, 2003). Currently, the dextral strike-slip component predominates in the San Andreas fault system.
Earthquake prediction
Published in Ömer Aydan, Earthquake Science and Engineering, 2023
As noted from Figure 10.26, compressive principal strain rates are perpendicular to the plate boundary between the Indian and Euro-Asian plates. It is interesting to note that the principal strain rates in the vicinity of Kabul are high and are close to the strain rate variations in the vicinity of sinistral faults. Furthermore, the strain rate to the north of the Hari-rud (Herat) Fault implies dextral-type straining in accordance with the deformation sense of this fault.
Seismic anisotropy for understanding the dynamics of crust and upper mantle
Published in Rajib Biswas, Recent Developments in Using Seismic Waves as a Probe for Subsurface Investigations, 2023
Figure 12.14 shows the average FPDs for the entire crust beneath nine stations obtained through Ps splitting. The orientation of the bar represents FPD whereas the length of the bar is proportional to delay times. The Ps-splitting analysis (Figure 12.14) shows more consistent FPDs compared to S-wave splitting. The FPDs are parallel or sub-parallel to the Karakoram Fault and other NW-SE trending tectonic features existing in the region. The strength of anisotropy estimated for the whole crust is higher (maximum delay time δt: 0.75 s) in comparison to the upper crust. This indicates that the dominant source of anisotropy in the Trans-Himalayan crust is confined within the middle and lower crustal depths. The predominant NW-SE trending FPDs consistently observed in the upper crust as well as in the middle and lower crust near the Karakoram Fault zone support the fact that the Karakoram Fault is a crustal-scale fault that extends at least up to the lower crust. Dextral shearing of the Karakoram Fault creates shear fabric and preferential alignment of mineral grains along the strike of the fault, resulting in the observed FPDs. A similar observation in the Indus Suture Zone (ISZ) also suggests crustal-scale deformation owing to the India-Asia collision. NW-SE trend of FPDs observed in upper as well as middle and lower crust near the KFZ suggests coherent deformation throughout the crust. This also indicates that the Karakoram Fault is a crustal-scale fault that extends at least up to the lower crust. Dextral shearing of the Karakoram Fault creates shear fabric and preferential alignment of mineral grain along the fault which causes the observed FPD. The results suggest the predominance of structure-induced anisotropy rather than anisotropy originated due to compressive stress (Paul et al., 2017).
Strain localisation and transcurrent reactivation in the granulite facies Kalinjala Shear Zone at Port Neill, South Australia
Published in Australian Journal of Earth Sciences, 2022
C. J. L. Wilson, J. R. Stewart, P. G. Betts
There is an increase in the long-wavelength magnetic gradient towards the east, which corresponds to a gradient in the Bouguer gravity data (Figure 23a–c). These gradients are interpreted to reflect a transition from an inferred thick sequence of non-outcropping Hutchison Supergroup rocks and non-magnetic granite in the west to high-grade, denser amphibolites and gneisses of the Sleaford Complex, adjacent to the Kalinjala Shear Zone. Discrete linear and elliptical high-amplitude aeromagnetic anomalies to the west of the Kalinjala Shear Zone show complex and Type III interference patterns, and possible sheath folds have been recognised (cf. Vassallo & Wilson, 2002, figure 15). The earliest generation of folds (KF1) trend approximately east–west to north–south and are tight to isoclinal (Vassallo & Wilson, 2001). These are overprinted by north–south-trending KF2 folds (Figure 21a). The axial traces of the north–south folds are perturbed by the Kalinjala Shear Zone, indicating dextral kinematics along the shear zone (Figure 21a). Overprinting, west-northwest- to east-southeast-trending large-scale open folds (Figure 21a) correlate with KD3 in the Port Neil area. Sets of northwest- and northeast-trending conjugate faults in the central part of the Kalinjala Shear Zone are interpreted to overprint KF2 axial traces and formed during approximate east–west shortening associated with the brittle/ductile deformation phase late in KD2.
Map-view restorations of the South Island, New Zealand: a reappraisal of the last 10 Myr of evolution of the Alpine and Wairau faults
Published in New Zealand Journal of Geology and Geophysics, 2022
Strike-slip separation of c. 150 km is restored on the Alpine Fault for this stage, as measured between the southern and northern cut-offs (C and C’) of the reverse faults 1–5 from Otago to the Glenroy-Matakitaki Block (Figure 10 and Table S2). If dextral slip on the Alpine Fault started at c. 25–23 Ma (Table S1), this separation implies average slip rates ≤ 10–12 mm/yr over the first 15–13 Myr of fault activity. Reverse faults 1–5 are reconstructed with sub-parallel NNW-SSE orientation (Figure 10), but the correlation of fault 5 from Otago to Marlborough (see also Figure 5) and its inferred cross-cutting of fault 4 (Moonlight fault) are speculative. A panel of Caples units bounded by faults 3 and 4 has been added above the Rakaia units in Otago and Marlborough, and the Caples-Rakaia boundary has been inferred to extend between the Marlborough and Wellington-Wairarapa blocks.
Has the tectonic regime of the Baltic Shield always remained the same?
Published in GFF, 2022
The Karelian craton (Fig. 6) is considered Archean with only insignificant Proterozoic reworking, whereas the Norrbotten lithotectonic unit (Fig. 6) is strongly reworked, involving significant Proterozoic magmatism and metamorphism leading to a complicated picture (Bergman & Weihed 2020). The boundary towards the Bothnia-Skellefte lithotectonic unit (Fig. 6) is drawn according to Öhlander et al. (1993), but it is not well constrained (Bergman & Weihed 2020). Sedimentary rocks intruded by granitoids characterize the Bothnia-Skellefte unit. In its central part, schist is the dominated rock type (Lundqvist et al. 1990; Lindh 2014), whereas in central Finland, close to the Archean boundary, the metamorphism reaches low-pressure granulite facies (Hölttä 1988). Ore-associated, silicic volcanic rocks are important at the northern boundary. To the south follows the Ljusdal tectonic unit with metamorphism locally reaching low-pressure granulite facies (Fig. 6, Högdahl & Bergman 2020). Its boundaries are defined by dextral transpressive zones, the Hassela Shear zone in the north and the Hagsta Gneiss and Storsjön-Edsbyn zones in the south (Fig. 6).