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Damage zone about 6 m long at the tip of a left-lateral strike-slip fault. The segmented master fault strikes about N1008, with antithetic faults and extension fractures striking about N0408 and N0708, respectively.
Source publication
Well-exposed strike-slip faults in limestones in the north-western part of Gozo show damage zones that can be grouped into three categories based on their location along faults; tip damage, linking damage and distributed damage. The predominant fracture types within damage zones include extension fractures and secondary faults. Tip damage zones usu...
Contexts in source publication
Context 1
... antithetic faults shown in Fig. 7 show several extension fractures with smaller antithetic faults. Antithetic faults dominate away from the tip of the master fault, with several wedge-shaped zones of higher order (i.e. smaller) antithetic faults developed at some fault tips. Several second-order synthetic faults crosscut antithetic faults (Fig. 7). Various studies ...
Context 2
... antithetic faults shown in Fig. 7 show several extension fractures with smaller antithetic faults. Antithetic faults dominate away from the tip of the master fault, with several wedge-shaped zones of higher order (i.e. smaller) antithetic faults developed at some fault tips. Several second-order synthetic faults crosscut antithetic faults (Fig. 7). Various studies (McKinstry, 1953;Moody and Hill, 1956;Chinnery, 1966b;Arboleya and Engelder, 1995;Willemse et al., 1997;Davis et al., 2000) have described higher-order faults and extension fractures, which are similar to those developed around secondary antithetic faults in the study area (Figs. 5 -7). ...
Citations
... Conjugate faults may be combined with branch faults (see below) and create block rotation (e.g. Nicholson et al., 1986;Kim et al., 2003). d) Branch faults: They represent shear fractures having similar sense of motion as the main strike-slip zone (dextral strike-slip in our case, blue patch in Figure 7). ...
The two moderate earthquakes that occurred close and to the north of the North Aegean Trough (NAT) on 26 September 2020 (Mw5.3) and 16 January 2022 (Mw5.4), both followed by aftershock activity, are examined. Seismic activity along the NAT and its parallel branches is continuous and remarkable, with numerous strong instrumental (M≥6.0) earthquakes. Yet, the frequency of moderate (5.0≤M<6.0) earthquakes outside these major fault branches is rather rare and therefore their investigation provides the optimal means to decipher the seismotectonic properties of the broader area. The temporal and spatial proximity of the two seismic excitations from late September of 2020 through early 2022, intrigues for exhaustive investigation of seismic activity with the employment of earthquake relocation techniques, moment tensor solutions and statistical analysis. Our research revealed that this seismic activity purely falls inside the Mainshock-Aftershock type, with fast aftershock decay rates and moderate productivity. According to our findings, the two seismic sequences, despite their close proximity, exhibit distinctive features as a result of the intricate stress field generated at the western termination of the NAF system in an extensional domain.
... Some prominent strike-slip faults reported around the world do have branch fractures combined with antithetic faults at their tips or where multiple stepping strike-slip features interact (e.g. Kim et al. 2003), but these are small and result in a series of parallel rotated blocks. Large-scale strike-slip faults can have normal faults at their tips, for example, the La Tet Fault, eastern Pyrenees (Cabrera et al. 1988), which are commonly straight and have an angle of c. 40-50° to the master fault (Kim and Sanderson 2006). ...
The Sibela Mountains of the island of Bacan in eastern Indonesia contain one of the Earth’s youngest metamorphic complexes that is now exposed at elevations up to 2000 m. New mica ⁴⁰ Ar/ ³⁹ Ar and apatite (U–Th–Sm)/He data from metamorphic and igneous rocks indicate that these rocks were rapidly exhumed in the Pleistocene (c. 0.7 Ma). Exhumation of the metamorphosed Permo-Triassic basement (c. 249–257 Ma) was accompanied by metamorphism (recorded by schists) as well as partial melting (recorded by c. 1.4 Ma granitic dykes). These processes must have occurred at extremely high cooling and exhumation rates. The rapid exhumation on land was associated with significant subsidence in adjacent basins offshore that reach depths up to 2.4 km. Neogene metamorphic core complexes and other metamorphic complexes are well-known from eastern Indonesia, but they usually record much higher exhumation rates than those reported from older classic metamorphic core complexes found in other parts of the world and require a different formation mechanism. Unlike classic metamorphic core complexes that are characterized by low-angle detachment faults, the Bacan metamorphic rocks were exhumed on steep bounding normal faults forming a rectilinear block pattern. We suggest such complexes are termed metamorphic block complexes (MBC). The Bacan MBC is exceptionally young and like the other east Indonesian complexes was rapidly exhumed during subduction rollback. A flexure formed during arc-arc collision as the Sangihe forearc loaded the Halmahera forearc which reactivated steeply-dipping faults in a rectilinear chocolate block pattern.
Graphical abstract
... Shear fractures and faults are widespread in the brittle Earth's crust and are documented by earthquake activity in the compressive stress regime (Kim et al. 2003). In contrast, tensile fractures require specific geological conditions with low confining stresses, such as dike intrusion, volcanic magma rise, and geothermal unrest (Einstein 2021). ...
The distinction between the shear behavior of tensile- and shear-induced fractures is critical to understanding the deformation and failure of geologic discontinuities at different scales. To investigate these differences, a series of direct shear tests were performed on sandstone specimens with a continuous fracture created by either splitting or shearing. The acoustic emission (AE) technique was used to examine variations in grain-size cracking behavior between specimens with tensile- and shear-induced fractures. An increase in normal stress for both fracture types correlates with increased microcrack density and energy release. However, there are notable differences: during the shear process, tensile-induced fractures produce AE sequences similar to the seismic patterns observed along natural tectonic faults, with foreshocks, mainshocks, and aftershocks. In contrast, the AE sequence for shear-induced fractures during the shear process lacks prominent mainshocks and deviates progressively from the power-law function with time as normal stress increases. In addition, the AE b-value for tension-induced fractures initially shows a gradual decrease as the mainshock approaches and then slowly increases during the aftershock period. In contrast, the b-value remains nearly constant for shear-induced fractures due to the low roughness and heterogeneity of the fracture surface. These differences highlight the strong correlation between AE responses and fault heterogeneity, paving the way for fault characterization and risk assessment in subsurface energy extraction.
... There, the faults display characteristics of strike-slip faults formed by shear failure in an intact medium (neoformed faults) (Nkodia et al., 2020). They appear in a similar way as the mesoscale strike-slip faults and associated fractures observed by Kim et al. (2003) in limestone are further generalized for various lithotypes (Kim et al., 2004): branching faults or extension fractures at a fault tip, damage zones with extension fractures and secondary faults linking damage zones between offset fractures forming pull-aparts in a strike-slip fault system, and distributed damage zones typical of the Riedel shear pattern ( Fig. 9d; Nkodia et al., 2020). In cross-section, they often display a typical duplex and flower structure (e.g. ...
The history of brittle faulting and associated paleostress states has been investigated in the rapids of the Congo
River at the outlet of the Malebo Pool between Kinshasa (Democratic Republic of the Congo) and Brazzaville
(Republic of the Congo). The aim of this study was to unravel the Meso-Cenozoic tectonic evolution of the
western margin of Central Africa, as well as to investigate the dynamic evolution of the Pool and the capture of
the Congo Basin drainage system by the Lower Congo River through the Central African Atlantic swell that
formed between the Congo Basin and the Atlantic Ocean. We reviewed the geological evolution of the Pool area
using recent data and new field observations to develop a consistent stratigraphic model for both sides of the
Congo River. We collected a significant amount of data faults and fractures in the early Paleozoic Inkisi arkosic
sandstones, identified four successive data subsets and determined their related paleostress tensors trough an
iterative process utilizing relative chronological indications. All paleostress states exhibit a a strike-slip faulting
regime, with varying orientation of horizontal principal compression. The timing of faulting was constrained by
indirect observations based on the updated understanding of the Pool’s evolution. The geodynamic interpretation of the brittle stages considered potential sources of compressional stress arising from plate boundaries and
from the oceanic ridge push. A polyphase brittle tectonic history was identified, characterized by the gradual
appearance of newly formed faults and reactivation of the existing ones, leading to the gradual saturation of the
host rock with fractures. The most recent event let to a significant imprint on the current landscape and is
believed to have facilitated the connection of the drainage system of the Congo Basin to the Atlantic coast in the
Oligocene period. The current stress state, determined from earthquake focal mechanisms, aligns with the most
recent paleostress state identified determined from fault-slip data, displaying similar stress axis orientations but
with consistent with a transpressional stress regime instead of a strike-slip one.
... This group consists mainly of shear fractures (R, R', and P shear fractures) as well as extensional fractures (T). Each fracture type forms at different stages and conditions during the development of a strike-slip fault (Davis et al., 2000;Kim, 2001;Kim et al., 2003;Fossen, 2010). ...
We describe the orientation, number, size, distribution, and fracture spatial arrangement in the central part of the kilometric Tuxtla-Malpaso fault system, one of the largest in the south of Mexico which cuts Cretaceous calcareous rocks. In this area, there are two sub-vertical extensional fracture sets (T1 and T2). The T1 fractures have ∼ N–S orientation and recorded 4.48 % of extension. The T2 fractures cut the T1 fractures, have NE-SW orientation, and accommodate an amount of extension of 3.87 %. These two fracture sets are parallel to two normal fault groups. The youngest normal faults (F2) have NE-SW strike and cut the N–S normal faults (F1). The F1 faults record a reactivation as strike-slip faults contemporaneous with F2.
The T1 and T2 fractures have a fracture intensity between 9.08 and 9.39 (P10) on mesoscopic scale. In the case of the spacing, the value of this parameter (0.28–1) is related to fracture clustering. This behavior agrees with the values of fractal box dimension (0.72–0.81), correlation dimension (0.24–0.6), Lyapunov exponent (1.31–2.42), and coefficient of variation (0.94–1.85) on mesoscopic scale. The cumulative aperture vs. distance shows that T1 and T2 fractures have heterogeneous strain distribution. The fracture spatial arrangement is verified with the normalized correlation count analysis (NCC). The NCC graphs show a clustering behavior for T1 and T2 fractures, which are related to a regulary-spaced fractal clusters pattern. We suggest that this pattern is related to the mechanical stratigraphy and the strain location in the fault zones, while the fracture intensity depends on the degree of fracture clustering and rock type more than the amount of strain.
Finally, the T1 fractures were associated with the right strike-slip kinematic for the NW-SE Tuxtla-Malpaso fault. This activity recorded a transtension behavior during the middle Miocene. The T2 fractures were formed during the reactivation (Pliocene) of the Tuxtla-Malpaso fault as the left strike-slip fault behind wrenching-transpression kinematics.
... The study of unconnected, discontinuous fractures can be traced back to the macroscopic scale, where scholars extensively research natural phenomena such as en echelon faults, segmented fractures, and en echelon vein array ( Figure 3) [40][41][42]. Early studies investigated the generation and evolution mechanisms of en echelon faults at the macroscopic scale based on exposed joints, fissures, and fault zones [43]. ...
The fracture network generated by hydraulic fracturing in unconventional shale reservoirs contains numerous microfractures that are connected to macroscopic fractures. These microfractures serve as crucial pathways for shale gas to flow out from micro- and nano-scale pores, playing a critical role in enhancing shale gas recovery. Currently, more attention is being given by academia and industry to the evolution of macroscopic fracture networks, while the understanding of the microfracture mechanisms and evolution is relatively limited. A significant number of microfractures are generated during the hydraulic fracturing process of shale. These microfractures subsequently propagate, merge, and interconnect to form macroscopic fractures. Therefore, studying the fracture process of rock masses from a microscale perspective holds important theoretical significance and engineering value. Based on the authors’ research experience and literature review, this paper provides a brief overview of current progress in shale microfracture research from five aspects: in situ observation experiments of microfractures in shale, formation and evolution processes of discontinuous microfractures, the impact of inhomogeneity on microfracture propagation, measurement methods for microscale mechanical parameters and deformation quantities in shale, and numerical simulation of shale microfractures. This paper also summarizes the main challenges and future research prospects in shale microfracture studies, including: (1) quantitative characterization of in situ observation experimental data on shale microfractures; (2) formation and evolution laws of macroscopic, mesoscopic, and microscopic multi-scale discontinuous fractures; (3) more in-depth and microscale characterization of shale heterogeneity and its deformation and fracture mechanisms; (4) acquisition of shale micro-mechanical parameters; (5) refinement and accuracy improvement of the numerical simulation of microfractures in shale. Addressing these research questions will not only contribute to the further development of microfracture theory in rocks but also provide insights for hydraulic fracturing in shale gas extraction.
... Thereafter, the formation of diapiric pointing as an intersection/linking damage zone and cross-node (Kelly et al., 1998;Manzocchi, 2002;Nixon et al., 2012;Sanderson and Nixon, 2015;Peacock et al., 2016), resulting along E-W principal right slip motion displacement zone (PDZ) can be explained by the linking conjugate pre-existing faults and the East-tending right-slip shear motion. Instead, a long E-W shear zone, cross-node resulting from the EW and NE-SW Connecting faults, assists a link damage zone (McGrath and Davison, 1995;Kim et al., 2003Kim et al., , 2004Choi et al., 2016;Wu et al., 2018). This is what mobilizes the Triassic extrusions at these points of weakness. ...
This scientific study aims to investigate the geological characteristics and tectonic processes of the central Tunisian Atlas region, focusing on the influence of tectonic events related to the Jurassic-Early Cretaceous Tethyan rifting and the subsequent Cenozoic tectonic inversion and uplift. In particular, this research emphasizes the strong control of tectono-sedimentary events on the geology of the central Tunisian Atlas, with specific attention given to the understudied isolated salt-related structures. To gain insights into the relationship between deep-seated faults, salt tectonism, and the conjugate strikes-slip faults, this study is based on subsurface data, including 2D seismic reflection and gravity data. The analysis investigates, the location of salt extrusions in relation to fault intersections. Results derived from subsurface data indicate that diapiric intrusions primarily occur at the junctions of major fault systems likely inherited from the Triassic-Jurassic Tethyan period. Notably, salt migration was remarkably active during the early Cretaceous, as evidenced by halotectonic sequences and salt-related mini-basins. Furthermore, fault blocks display sedimentary infill above tilted blocks, where salt structures appear to occur at their peripheries. During the subsequent tertiary compressions, the structural configurations of the basin (i.e., Z-shape basin) promote the strike-slip movement along pre-existing faults. This new structural interpretation suggests a closely relationship between fault zones inherited from the Jurassic-Early Cretaceous Tethyan Opening and isolated salt-related structures. The subsequent Cenozoic shortening events, including the Atlassic and Alpine events, have led to uplift of the deep-seated faults, facilitating the ascension and deformation of Triassic evaporitic sediments within subcircular isolated structures. Field observations and seismic sections indicate the presence of sedimentary gaps resulting from these processes. The findings of this study contribute to a comprehensive understanding of the deep tectonic framework and shallow salt-related structures in the central Tunisian Atlas.
... Numerous studies describe that during deformation events, the geometric development of fractures and their relative abundance expressed as density (fracture number per unit length or unit area) and intensity (fracture length per unit area or unit volume) can be controlled by lithology and mechanical stratigraphy as well as structural position (e.g., [4][5][6][7][8][9][10][11][12][13][14][15][16]). An increase in fracturing and relative complexity is typically observed within the damage zone of faults due to nucleation, propagation, and offset accommodation of the different brittle structures that are related to the faulting mechanism (e.g., [17][18][19][20][21][22][23][24][25][26]). ...
In the frame of a regional study that is aimed at defining the landslide susceptibility in the upper Susa Valley (Western Italian Alps), this paper investigated the variation in the fracture network of rock masses in correspondence to faults zones. Fracture networks were characterized at sites located along transects that are oriented normally to fault traces and scattered in their adjacent sectors with the scope to be able to define and estimate the variation in fracture abundance in the bedrock. Fracture collection using a traditional geomechanical survey was combined with topological analysis to estimate the degree of fracturing of rock masses in terms of fracture intensity (P21) and connectivity. Several sites were selected, and the variation in fracturing intensity values and degree of connectivity allowed for the defining of “high fracturing zones” (HFZ) near fault traces moving from the background values of adjacent rock masses. Considering the variation in fracture intensity, a range of 400 m to 150 m HFZ can be defined, with considerable differences between the areas analysed. The values recorded show a high irregular variability in fracture intensity in correspondence to the mapped faults due to the interference and overlay of structures related to the complexity setting of the fault damage zone.
... Thereafter, the formation of diapiric pointing as an intersection/linking damage zone and cross-node (Kelly et al., 1998;Manzocchi, 2002;Nixon et al., 2012;Sanderson and Nixon, 2015;Peacock et al., 2016), resulting along E-W principal right slip motion displacement zone (PDZ) can be explained by the linking conjugate pre-existing faults and the East-tending right-slip shear motion. Instead, a long E-W shear zone, cross-node resulting from the EW and NE-SW Connecting faults, assists a link damage zone (McGrath and Davison, 1995;Kim et al., 2003Kim et al., , 2004Choi et al., 2016;Wu et al., 2018). This is what mobilizes the Triassic extrusions at these points of weakness. ...
This scientific study aims to investigate the geological characteristics and tectonic processes of the central Tunisian Atlas region, focusing on the influence of tectonic events related to the Jurassic-Early Cretaceous Tethyan rifting and the subsequent Cenozoic tectonic inversion and uplift. In particular, this research emphasizes the strong control of tectono-sedimentary events on the geology of the central Tunisian Atlas, with specific attention given to the understudied isolated salt-related structures. To gain insights into the relationship between deep-seated faults, salt tectonism, and the conjugate strikes-slip faults, this study is based on subsurface data, including 2D seismic reflection and gravity data. The analysis investigates, the location of salt extrusions in relation to fault intersections. Results derived from subsurface data indicate that diapiric intrusions primarily occur at the junctions of major fault systems likely inherited from the Triassic-Jurassic Tethyan period. Notably, salt migration was remarkably active during the early Cretaceous, as evidenced by halotectonic sequences and salt-related mini-basins. Furthermore, fault blocks display sedimentary infill above tilted blocks, where salt structures appear to occur at their peripheries. During the subsequent tertiary compressions, the structural configurations observed in this fold-and-thrust belt incorporate the pre-existing salt structures. This new structural interpretation suggests a closely relationship between fault zones inherited from the Jurassic-Early Cretaceous Tethyan Opening and isolated salt-related structures. The subsequent Cenozoic shortening events, including the Atlassic and Alpine events, have led to uplift of the deep-seated faults, facilitating the ascension and deformation of Triassic evaporitic sediments within subcircular isolated structures. Field observations and seismic sections indicate the presence of sedimentary gaps resulting from these processes. The findings of this study contribute to a comprehensive understanding of the deep tectonic framework and shallow salt-related structures in the central Tunisian Atlas.
... This material produces fractures which are observable at the model surface, as < 20 mm long and <1 mm open troughs (see supplementary material, Fig. S1), that generally correspond at depth in the model to very small disaggregation shears (<1 mm, see Supplementary Material Fig. S2). These fractures are qualified in this study as small segments or secondary faults (in the sense of Maerten et al., 2002;Kim et al., 2003Kim et al., , 2004, often having a shear component whose shear/opening ratio increases with their development and similar to those observed on rocks in shear box tests (Wibberley et al., 2000). Major faults developed further by a cumulative displacement of several millimeters (>100 m in nature) and a length of several tens of centimeters (>10 km in nature). ...
