Results Of Analogue Models Research Articles

Effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts—New insights from analogue modelling

Studying fold-and-thrust belts is crucial in geoscience; fold-and-thrust belts are rich in petroleum and natural gas. However, the effects of friction properties and rheological structures on the deformation patterns and evolution of fold-and-thrust belts with two detachment layers are less frequently discussed. Therefore, using models with a basal silicone layer, a middle silicone layer and overlying quartz sand layers, this study conducted an analogue modelling analysis of the effects of friction conditions, rheological structures and compressional velocity on the deformation and evolution of fold-and-thrust belts. The results show the following. 1) The weak layer or low friction strength of the basement forms complex deformations of the structural style, forming forward thrust, backward thrust, symmetrical pop-up structure and frontward–backward oscillating structural characteristics. 2) The friction strength ratio between the lateral and basement layers does not determine the structural style of a fold-and-thrust belt; moreover, it is closely related to the construction of strata or rheological structures. 3) The deformation of double detachment layers complicates the structural style of fold-and-thrust belts. 4) The analogue modelling results are similar to the structural style of the simple fold belt of the Zagros fold-and-thrust belt (ZFTB), indicating that deep and middle detachment layers control the current deformation of the ZFTB.

Structural evolution and mechanism of multi-phase rift basins: A case study of the Panyu 4 Sag in the Zhu Ⅰ Depression, Pearl River Mouth Basin, South China Sea

The study of changes in normal fault systems during different rift stages is important to understand the genesis and evolution of multi-phase rift basins, such as the Panyu 4 Sag in the Zhu Ⅰ Depression. Using 2D and 3D seismic data and analogue modelling, the Zhu Ⅰ Depression was characterized as a series of half-grabens bounded by NE-NEE-trending normal faults, it was found to have undergone two phases of the extension during the Paleogene. The Zhu Ⅰ Depression exhibited four fault sets with different strikes, including NNE, NE-NEE, EW, and NWW. The main controlling faults were NE-trending and EW-trending with high activity rates during Rift Phase 1 and Rift Phase 2, respectively. The average azimuths of the dominant strikes for type Ⅰa, type Ⅰb, and type Ⅱ faults were 75°, 85°, and 90°, which revealed that the minimum principal stress (σ3) directions during the rift phases 1 and 2 of the Zhu Ⅰ Depression were SSE (∼165°) and near-EW (∼180°), respectively. Two phases of structural-sedimentary evolution, with different directions and analogue modelling results, illustrated that the Panyu 4 Sag was formed as a superimposed basin under multi-phase anisotropic extension. The structural evolution of the Panyu 4 Sag since the Paleogene was mainly controlled by the combined effects of the Pacific, Eurasian, and Indian plates. Since the orientation of subduction of the Pacific plate changed from NNW to NWW, the stress field shifted from NW-SE-trending tension to S-N-trending tension, causing the superimposition of late near-E-W-oriented structural pattern on the early NE-oriented structural pattern.

Sandbox models of fault-bend folding: A new investigation with a pre-existing fault ramp

This study presents the results of analogue models of fault-bend folds (FBFs) developed over a pre-existing fault dip ramp with a non-outcropping upper fault flat. To determine the boundary conditions that control the formation of FBFs, experiments were performed with quartz sand and glass microbeads, both with and without intercalations of thin horizons of mica flakes. We varied the initial thickness, the ramp dip angle, and the basal friction coefficient of the lower fault flat. The analogue models revealed that the most important factor for the formation of FBFs was the rheological behaviour of the analogue material. The elasto-plastic frictional behaviour of the glass microbeads is fundamental for the formation of Mode I-FBFs (with interlimb angles higher than 90°), which is independent of the angle of the pre-existing fault ramp and the basal friction along the lower fault flat. In the sand models, the formation of FBFs requires a high initial stratigraphic thickness, resulting in a significant increase in the normal stress and/or in the cohesion strength. In glass microbeads, the models developed structures very similar to the FBFs described in the carbonates of the Maracaibo Basin (Venezuela) as well as those within the Appalachian thrust belt (USA).

A quantitative analysis of transtensional margin width

Continental rifted margins show variations between a few hundred to almost a thousand kilometres in their conjugated widths from the relatively undisturbed continent to the oceanic crust. Analogue and numerical modelling results suggest that the conjugated width of rifted margins may have a relationship to their obliquity of divergence, with narrower margins occurring for higher obliquity. We here test this prediction by analysing the obliquity and rift width for 26 segments of transtensional conjugate rifted margins in the Atlantic and Indian Oceans. We use the plate reconstruction software GPlates (www.gplates.org) for different plate rotation models to estimate the direction and magnitude of rifting from the initial phases of continental rifting until breakup. Our rift width corresponds to the distance between the onshore maximum topography and the last identified continental crust. We find a weak positive correlation between the obliquity of rifting and rift width. Highly oblique margins are narrower than orthogonal margins, as expected from analogue and numerical models. We find no relationships between rift obliquities and rift duration nor the presence or absence of Large Igneous Provinces (LIPs).

Tectonics-mineralisation relationships within weak continental lithospheres: a new structural framework for Precambrian cratons

Many Archaean and Paleoproterozoic cratons show deformation patterns that differ from those observed in modern orogens. On the other hand, they constitute an important part of present-day emerged continents and contain a large part of continental mineral resources known to date. On the basis of a summary of structural data from some typical field examples and of results of analogue modelling, we emphasize that pop-down tectonics marked by vertical burial of supracrustals within an underlying hot and weak crust may be the most suitable model to account for deformation patterns of many ancient deformation zones. An overview of relationships between structural patterns and mineralisation in several ancient deformation zones further emphasizes that pop-down tectonics provides a very promising structural framework for mining exploration in Precambrian cratons.

Numerical solution of fractional variable order linear control system in state-space form

Abstract The aim of this paper is to introduce a matrix approach for approximate solving of non-commensurate fractional variable order linear control systems in state-space form. The approach is based on switching schemes that realize variable order derivatives. The obtained numerical solution is compared with simulation and analog model results.

Forced folding above shallow magma intrusions: Insights on supercritical fluid flow from analogue modelling

Magma emplacing at shallow crustal levels may cause significant deformation in the overlying country rock (i.e., forced folding, fracturing and faulting), both at a local and/or regional scale. To get insights into these processes, we investigated in the laboratory the development of forced folds and associated fracture/fault networks. An analogue magma, simulated by polyglycerols, was intruded into a sand pack representing the brittle crust. The scaled analogue models reproduced different 3D deformation structures depending on the model parameters (e.g., magma viscosity, injection rate, volumetric flux, and the rheology and thickness of the host and cover rocks). However, all models support the observation that the emplacement of shallow magmatic bodies may result in the growth of dome-shaped forced folds, and associated development of tensional and compressional deformation in the host-rock. Although the models involve simplifications, these results provide useful hints for geothermal research, as fractures and faults associated with magma emplacement can significantly influence the distribution and migration of superhot geothermal fluids. These structures can therefore be considered potential targets for geothermal and/or ore deposit exploration. In this perspective, the results of analogue models may provide useful geometric constraints for field work, numerical modelling, and particularly seismic interpretation, allowing production and a better understanding of integrated conceptual models concerning the circulation of supercritical fluids.

Analogue modelling of thrust systems: Passive vs. active hanging wall strain accommodation and sharp vs. smooth fault-ramp geometries

We present new analogue modelling results of crustal thrust-systems in which a deformable (brittle) hanging wall is assumed to endure passive internal deformation during thrusting, i.e. exclusively as a consequence of having to adapt its shape to the variable geometry of a rigid footwall. Building on previous experimental contributions, we specifically investigate the role of two so far overlooked critical variables: a) concave-convex (CC) vs. flat-ramp-flat (FRF) thrust ramp geometry; and b) presence vs. absence of a basal velocity discontinuity (VD). Regarding the first variable, we compare new results for considered (CC) smoother ramp types against classical experiments in which (FRF) sharp ramp geometries are always prescribed. Our results show that the considered sharp vs. smooth variation in the thrust-ramp geometry produces important differences in the distribution of the local stress field in the deformable hanging wall above both (lower and upper) fault bends, with corresponding styles of strain accommodation being expressed by marked differences in measured morpho-structural parameters. Regarding the second variable, we for the first time report analogue modelling results of this type of experiments in which basal VDs are experimentally prescribed to be absent. Our results critically show that true passive hanging wall deformation is only possible to simulate in the absence of any basal VD, since active shortening accommodation always necessarily occurs in the hanging wall above such a discontinuity (i.e. above the lower fault bend). In addition, we show that the morpho-structural configuration of model thrust-wedges formed for prescribed VD absence conditions complies well with natural examples of major overthrusts, wherein conditions must occur that approximate a frictionless state along the main basal thrust-plane.

Analogue modeling of the role of multi-level decollement layers on the geometry of orogenic wedge: an application to the Zagros Fold–Thrust Belt, SW Iran

The presence of evaporate and incompetent formations (i.e., decollement horizons) within the sedimentary sequence of fold-thrust belts can control their structural style and deformation evolution. In the present study, the influence of the decollement layers (e.g., basal and internal decollement layers) on the deformation style of several segments of the Zagros Fold-Thrust Belt (ZFTB), SW Iran (e.g., Fars Arc, Dezful Embayment, and Izeh Zone) was investigated using a series of analogue models of accretionary wedges. The study of seismic profiles to understand the structural evolution of these segments of the belt, where several decollement intervals acted as basal and internal decollements, is complemented by the analogue model results. The experimental results reveal that the thickness of the internal decollement layers influences the creation of fold-dominated or thrust-dominated deformations, respectively. Experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation (in-sequence and/or out-of-sequence faults) into overlying strata towards southwest by fore-deformation and control the rate of deformation propagation in the ZFTB. The presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the ZFTB. In addition, the geometry, spacing, activity, and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low-frictional decollements (Geophys J Int, 165(1):336–356 2006; Geochem Geophys Geosyst, 14:1131–1155 2013). The seismic profiles of the ZFTB showed that in addition to lithological contrasts, the existence and activity of deep-seated and basement faults had a big impact on the structural styles of the region.

Topological characteristics of simple and complex normal fault networks

2-D, map-view topological analysis of ten natural and two analogue fault networks was undertaken. The fault arrays range from simple, low-displacement systems, to complex systems arising from multiple stages of deformation, or exhibiting complex local rotation of stresses. Classification of fault arrays was based on fault terminations (I-nodes), splaying and abutting geometries (Y-nodes) and cross-cutting relationships (X-nodes), which permit relatively quick and simple ways of analysing fault terminations and connectivity. Many of the fault networks are predominantly composed of I- and Y-nodes with at most only a minor X-node population, hence discrimination of significant differences between fault networks using just this type of analysis is limited. Subdividing Y-nodes into splaying (Ys), abutting (Ya) and cross-cutting (Yc) types, displaying the data on Ys-Ya-Yc node triangles, as well as generating equivalent networks defined by vertices and edges provides additional information for defining fault networks. Comparison of the Ys-Ya-Yc node triangle and the excess kurtosis of vertice degree distribution identifies seven distinct types of network that show meaningful differences. Such quantitative descriptions are useful for comparing the results of analogue and numerical models with natural examples as well as assessing fault network connectivity, which has implications for the structural interpretation of reservoirs and aquifers. A wide variety of factors contribute to variations in fault networks such as variations in strain, stress rotation with time, fabric inheritance, and stress deflection. While topology cannot be used to identify specific mechanisms, some topological characteristics can help narrow the likely mechanism particularly when used in conjunction with more traditional techniques and observations.

The structural evolution of the Radicondoli–Volterra Basin (southern Tuscany, Italy): Relationships with magmatism and geothermal implications

The Western Tuscany, in the inner sector of the Northern Apennines, is characterized by a thinned continental crust (∼20–25km), high heat flow (>100mWm−2), and the presence of magmatism. The latter produces the current geothermal activity, which is mostly localized at the large Larderello–Travale field settled above the granites with the same name. These features and the several Late Miocene sedimentary basins that developed in the area are normally related to an extensional tectonics that affected the back-arc area since the Early-Middle Miocene (∼16Ma), although, some geophysical studies image the continental crust deformed by W-dipping thrust faults. Here we present a new field survey conducted in the Radicondoli–Volterra Basin, which bounds the Larderello–Travale pluton system to the northeast. The results support former conclusions that the basin infill has been intensely shortened. Integrated analysis of other surrounding hinterland basins suggests that a phase of regional shortening affected the back-arc area approximately between 7.5 and 3.5Ma. This period partly overlaps with the emplacement of the Larderello–Travale granites that started no later than 3.8Ma, thus raising the possibility that compressive structures may have – at least in part – controlled magma emplacement, and/or also that the early emplacement of the Larderello–Travale granites occurred when the compressive stresses started to decay. In some cases, isotherms localize and elongate in the direction of subsurface anticlines in the basement, as occurs in the Travale area. Comparison with the results of analogue models indicates that the core of active and inactive fold anticlines in the basement may focus the upraising of magmatic fluids, with obvious implications for the geothermal exploration of the area.

Intrinsic versus extrinsic variability of analogue sand-box experiments – Insights from statistical analysis of repeated accretionary sand wedge experiments

Analogue models are not perfectly reproducible even under controlled boundary conditions which make their interpretation and application not always straight forward. As any scientific experiment they include some random component which can be influenced both by intrinsic (inherent processes) and extrinsic (boundary conditions, material properties) sources. In order to help in the assessment of analogue model results, we discriminate and quantify the intrinsic versus extrinsic variability of results from “sandbox” models of accretionary wedges that were repeated in a controlled environment. The extrinsic source of variability, i.e. the parameter varied is the nature of the décollement (material, friction and thickness). Experiment observables include geometric properties of the faults (lifetime, spacing, dip) as well as wedge geometry (height, slope, length).For each variable we calculated the coefficient of variance (CV) and quantified the variability as a symmetric distribution (Normal, Laplacian) or asymmetric distribution (Gamma) using a Chi squared test (χ2). Observables like fault dip/back thrust dip (CV = 0.6–0.7/0.2–0.6) are less variable and decrease in magnitude with decreasing basal friction. Variables that are time dependent like fault lifetime (CV = 0.19–0.56) and fault spacing (CV = 0.12 – 0.36) have a higher CV consequently affecting the variability of wedge slope (CV = 0.12–0.33). These observables also increase in magnitude with increasing basal friction. As the mechanical complexity of the evolving wedge increases over time so does the CV and asymmetry of the distribution. In addition, we confirm the repeatability of experiments using an ANOVA test. Through the statistical analysis of results from repeated experiments we present a tool to quantify variability and an alternative method to gaining better insights into the dynamic mechanics of deformation in analogue sand wedges.

Geological and geodetic constraints on the active deformation along the northern margin of the Hyblean Plateau (SE Sicily)

A geologic and geodetic integrated analysis of the northern margin of the Hyblean Plateau (SE Sicily) has been carried out in order to test the relationship between the active deformation, recorded by GPS data, and the long-term tectonic evolution, reconstructed by the interpretation of structural and morphological data. Our study revealed the active growth of a large antiform, as a consequence of the positive tectonic inversion of the previous flexure, bordering the Hyblean Foreland. The deformation of Middle–Late Pleistocene marine terraces and the evolution of the drainage system are consistent with a progressive regional tilting of the entire eastern sector of the Hyblean Plateau (Siracusa Domain), representing the southern limb of the active antiform. The geometry of the Late Quaternary marine strandlines, compared with the results of analogue models, is compatible with the effects of the NW-ward propagation of a detachment fault at depth. The active deformation of the Hyblean region, coherent with the Nubia–Eurasia plate convergence, suggests to candidate the inverted tectonics at the northern border of the Hyblean Plateau as potential seismogenic sources of the area.

Insights from analogue modelling into the deformation mechanism of the Vaiont landslide

The Vaiont landslide (Southern Alps, Italy) represents one of the most catastrophic landslides in the world recorded in the modern history. The landslide, occurred on 9th October 1963, involved about 3×108m3 of rock that collapsed in an artificial lake: more than 1900 people died as a consequence of the tsunami produced by the sudden fall of the mass in the water.Despite the importance of this event, many aspects of the Vaiont rockslide still remain unexplained, particularly its fast emplacement. In order to obtain a better understanding of the Vaiont disaster, this paper focuses on the results of analogue models designed to get insights into the internal and surficial deformation patterns that characterized the sliding rock mass. Plan view reconstructions of surface model displacement reveal that the rock mass is subdivided into compartments with different relative movements and differential rotations, believed to have played a significant role in causing the fast collapse. The deformation of the analogue models, compared with geological cross sections and in-situ data, suggests that sliding of the rock mass was accomplished by the development of some new (or the reactivation of pre-existing) fractures into the rock mass.

Analogue modeling of the collapse of non-homogeneous granular slopes along weak horizons

In this study, we use results of analogue models to investigate the effect of the dip, location and thickness of a weak horizon on the stability/failure, kinematics and internal deformation of a granular slope. The models are systematically designed to simulate the collapse of non-homogeneous granular slopes by focusing on the spatial and temporal distribution of their internal deformation. Model results show that the presence of a weak horizon embedded within the granular slope has a significant influence on the granular failure, which is accommodated through different generation pulses that successively decrease in volume. However, the dip and stratigraphic location of the weak horizon dictate whether the weak horizon play a role during the failure or not. When the main failure surface is contained within a weak horizon, the dip and thickness of the weak horizon have a positive effect on the displacement of the failure mass, whereas a shallow-located weak horizon causes larger displacement of the failure mass during the collapse of granular slopes. In addition, the collapse of granular slopes results in the formation of different-generation normal faults and shortening structures (folds and thrusts) within the failure mass. The first-generation normal faults with a steep dip (about 60°) cut across the entire stratigraphy of the slope, whereas the later-generation normal faults with a gentle dip (about 40°) cut across the shallow units. The distribution of these internal structures within the failure mass is affected significantly by the dip, location and thickness of the weak horizon.

3D deformation in strike-slip systems: Analogue modelling and numerical restoration

Regional and local strike-slip systems in Chile are complex and pose interesting questions, such as the interaction between strike-slip and reverse faults, how they evolve, and the relationship between shortening, rotation and uplift. Within this context, we developed a new analytical method based on analogue and numerical modelling applied to 3D, pure and transtensional-transpressional strike-slip systems. Analogue modelling results indicate that in restraining stepovers of strike-slip fault systems, where antiformal pop-up structures are usually formed, pre-existent basement structures with a high angle to the main strike-slip fault will generate a higher rotation of blocks. However, when these structures are oriented at a high angle with respect to the main stress convergence vector, the rotation will be less and therefore a higher tendency to uplift will be produced. These results were applied to NW- and SE-striking basement faults oblique to N-S mega-thrust faults in central Chile (32o-35oS), for which we propose a simultaneous development based on the analogue model results. Moreover, we propose that strike-slip movement occurred on thrust faults in central Chile. Furthermore, we performed a numerical restoration of an analogue experiment which modeled a pure strike-slip system, and concluded that the restoration is very sensitive to shortening data as well as to rotational data. These results are extremely important for future numerical and regional analysis of strike-slip systems.

Analogue Modelling of Inverted Oblique Rift Systems

The geometric evolution of brittle fault systems in inverted oblique and offset rift systems has been simulated using scaled sandbox analogue models. Dry fine-grained quartz sand was used to represent the brittle upper crust. Extensional faults geometries in the models were governed by the geometry and orientation of a stretching zone at the base of the models. Oblique rift models were characterized by segmented en-echelon border fault systems trending parallel to the rift axis and the underlying zone of basement stretching. Offset rift models promoted highly-segmented border faults as well as offset sub-basins within the rift. In both types of models, intra-rift fault arrays were oriented sub-perpendicular to the extension direction. Inversion of the oblique and offset extensional models was achieved by horizontal shortening. This resulted in partial inversion of the border and intra-rift faults as well as the formation of new reverse faults. The geometries, distribution, orientations and number of these new reverse faults were strongly controlled by the earlier-formed fault extensional architectures. At the margins of the rift zone, shortening was mainly accommodated by partial inversion of the border faults together with the formation of hanging-wall bypass faults and footwall shortcut thrusts. Inversion of the offset rift models produced reactivation of the extensional accommodation zones as soft-linked transfer zones between new thrust faults. The analogue model results have been compared with natural inversion structures in the Atlas Mountains of Morocco and the Ukrainian Donbas fold belt. The analogue modelling results suggest that the High Atlas formed as the result of oblique inversion of an oblique rift system, and the contractional structures in the Ukranian Donbas belt were generated by partial inversion of the earlier-formed Donbas extensional graben via two major newly developed short-cuts that uplifted and exhumed the basin.

Fault architecture in the Main Ethiopian Rift and comparison with experimental models: Implications for rift evolution and Nubia–Somalia kinematics

The Main Ethiopian Rift (MER) offers a complete record of the time–space evolution of a continental rift. We have characterized the brittle deformation in different rift sectors through the statistical analysis of a new database of faults obtained from the integration between satellite images and digital elevation models, and implemented with field controls. This analysis has been compared with the results of lithospheric-scale analogue models reproducing the kinematical conditions of orthogonal and oblique rifting. Integration of these approaches suggests substantial differences in fault architecture in the different rift sectors that in turn reflect an along-axis variation of the rift development and southward decrease in rift evolution. The northernmost MER sector is in a mature stage of incipient continental rupture, with deformation localised within the rift floor along discrete tectono-magmatic segments and almost inactive boundary faults. The central MER sector records a transitional stage in which migration of deformation from boundary faults to faults internal to the rift valley is in an incipient phase. The southernmost MER sector is instead in an early continental stage, with the largest part of deformation being accommodated by boundary faults and almost absent internal faults. The MER thus records along its axis the typical evolution of continental rifting, from fault-dominated rift morphology in the early stages of extension toward magma-dominated extension during break-up. The extrapolation of modelling results suggests that a variable rift obliquity contributes to the observed along-axis variations in rift architecture and evolutionary stage, being oblique rifting conditions controlling the MER evolution since its birth in the Late Miocene in relation to a constant post ca. 11 Ma ~ N100°E Nubia–Somalia motion.

3D imaging of volcano gravitational deformation by computerized X-ray micro-tomography

Analogue models are commonly used to gain insights into large-scale volcano-tectonic processes. Documenting model surface topography and the three-dimensional (3D) aspect of deformation structures remains the greatest challenge in understanding the simulated processes. Here we present the results of volcano analogue models imaged with an X-ray computerized micro-tomography (μCT) system developed at the Ghent University Centre for Tomography (UGCT). Experiments simulate volcano deformation due to gravitational loading over a ductile layer, a process affecting many natural volcanoes built over a sedimentary substratum. Results show that μCT is able to provide a 3D reconstruction of the model topography with unprecedented resolution. Virtual cross sections through reconstructed models enable us to map the main structures at depth and to document the deformation of the brittle-ductile interface due to contrasting X-ray attenuation. Results for lateral spreading and vertical sagging into thin and thick ductile layers, respectively, are illustrated for circular cones and elongated ridges. Results highlight structural patterns not seen in previous models, such as: 1) the 3D form of a polygonal brecciated zone at the center of spreading cones; 2) the complete lack of such a zone in sagging cones; and 3) relay structures between graben-bounding faults in spreading cones. In addition, detailed imaging of tension gashes and of the flexure surface below sagging cones enables the 3D strain distribution to be explored. Experiments with non-cohesive and low cohesion granular materials present striking differences in surface topography and fault characteristics. Despite limitations associated with the scan duration, μCT reconstruction of analogue models appears a powerful tool for better understanding the complex 3D deformation associated with volcano-tectonic processes.

Influence of shear angle on hangingwall deformation during tectonic inversion

AbstractTectonic inversion is a common phenomenon in island arc settings, especially in back‐arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault‐related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep‐sided half‐graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn‐extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5° during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.