Analogue Models Research Articles

Multiscale Analogue Modelling of Clinching Process to Investigate Thickness Tolerance and Tool Misalignment

NEED—The effect of dimensional variability of sheet thickness (tolerance) and tool misalignment is poorly understood for the clinching process. Finite element analysis (FEA) is valuable but requires a lot of and is difficult to verify in this situation due to the asymmetrical geometry and nonlinear plasticity. OBJECTIVE—The objective of this work was to determine the effect of thickness tolerance, tool misalignment and sheet placement (top vs. bottom) in the clinching process, by use of analogue modelling with plasticine. METHOD—Experiments used a scaled-up punch and die, with plasticine as the analogue. Thickness tolerances were represented by sheet thicknesses of 11 and 7 mm, 12 and 8 mm, 8 and 12 mm and 13 and 9 mm for upper and lower sheets, respectively. Two types of lubricant were tested between sheets: glycerine and silicone oil. Angular variability was also introduced. Measured parameters were interlock (also called undercut) and neck thickness. Analogue results for deformation were compared with microscopy of metal clinching. FINDINGS—The results reveal that the multiscale analogue model is an efficient tool for studying the effect of dimensional deviation on a clinch joint. Thickness tolerance showed a critical relationship with interlock, namely a reduction to about half that of the nominal, for both maximum and least material conditions. Increased angular misalignment also reduced the interlock. Compared with glycerine, silicone oil tests showed reduced interlock, possibly the result of a lower coefficient of friction. ORIGINALITY—This work demonstrates the usefulness of analogue modelling for exploring process variability in clinching. The results also show that significant effects for sheet placement are ductility, lubricant (friction), thickness of samples and tool misalignment.

Application of The Classical Soliton Theory to Study the Dynamics in PassiveDispersed and Active-Relaxation Media During the Formation of a Twist in A Toroidal Plasma

In this paper we consider the possibility of using analog models to study the behavior of the evolution and dynamics of toroidal vortex flows. The current model based on coupled van der Pol generators is used as the main one. In this robot, based on nonlinear dynamics display Bernoulli presented the evolution of the Torus. The use of analog models makes it possible to trace the dynamics of vortex flows. In General, the presented results allow us to confidently assert that both in the experiment and in the theoretical consideration we are dealing with the same object - a strange attractor of the Smale – Williams type in a non-Autonomous oscillatory system. The available data suggest that it is an attractor of hyperbolic type, although, strictly speaking, this statement needs mathematical proof. The appearance of an example of a physical system with a hyperbolic chaotic attractor is of fundamental importance for the further development of nonlinear dynamics and its applications. This is, in a sense, a "breakthrough into the hyperbolic realm." Based on the inherent property of coarseness of hyperbolic attractors, we can build other examples of systems with hyperbolic chaos. The presence of such physical systems opens up opportunities for the application of a deeply studied branch of mathematics – hyperbolic theory, and also translates into practice the problem of comparative study of hyperbolic and non-hyperbolic chaos in theory and experiment. This system can be used to study toroidal vortex processes.

From Analog to Digital Computing: Is Homo sapiens’ Brain on Its Way to Become a Turing Machine?

The abstract basis of modern computation is the formal description of a finite state machine, the Universal Turing Machine, based on manipulation of integers and logic symbols. In this contribution to the discourse on the computer-brain analogy, we discuss the extent to which analog computing, as performed by the mammalian brain, is like and unlike the digital computing of Universal Turing Machines. We begin with ordinary reality being a permanent dialog between continuous and discontinuous worlds. So it is with computing, which can be analog or digital, and is often mixed. The theory behind computers is essentially digital, but efficient simulations of phenomena can be performed by analog devices; indeed, any physical calculation requires implementation in the physical world and is therefore analog to some extent, despite being based on abstract logic and arithmetic. The mammalian brain, comprised of neuronal networks, functions as an analog device and has given rise to artificial neural networks that are implemented as digital algorithms but function as analog models would. Analog constructs compute with the implementation of a variety of feedback and feedforward loops. In contrast, digital algorithms allow the implementation of recursive processes that enable them to generate unparalleled emergent properties. We briefly illustrate how the cortical organization of neurons can integrate signals and make predictions analogically. While we conclude that brains are not digital computers, we speculate on the recent implementation of human writing in the brain as a possible digital path that slowly evolves the brain into a genuine (slow) Turing machine.

The integrated history of repeated caldera formation and infill at the Okataina Volcanic Centre: Insights from 3D gravity and magnetic models

Multistage collapse caldera create complex geological structures that are often buried by kilometers of pyroclastic infill and late stage lava domes, making study of their origins difficult from outcrop alone. Here we present new gravity and aeromagnetic data compilations derived from terrestrial, lake and airborne surveys to investigate the buried internal structure of the Okataina Volcanic Centre (OVC) and interpret its stages of development. Magnetic highs (1300 nT) are caused by a combination of thick lava flows and domes that infill the collapse structures, and a deeper feeder structure/dyke complex that extends below the basement to at least 6 km depth. Magnetic lows caused by hydrothermal alteration are associated with topographically low areas near the topographic and structural collapse margins suggesting fluid circulation within the caldera exploits both deep and shallow structures. Several large rhyolite lava flows contain low magnetisation rims reflecting the glassy outer carapace and crystalline core.The gravity data show a − 62 mGal residual gravity low associated with the OVC, with the steepest gradients occurring inside the topographic margins. The gradient of the gravity low is stepped towards its lowest point near the outlet of Lake Tarawera. Each step is interpreted as relating to the buried structural collapse margins of the Utu, Matahina, Rotoiti and possibly Kawerau, catastrophic caldera forming eruptions, creating an overlapping and nested caldera structure, however there is no evidence for an OVC encircling ring structure. Buried caldera margins associated with oldest Utu eruption may play a role in the location of the youngest Tarawera eruptions. We propose smaller amplitude gravity lows that extend outside the topographic margins of the caldera are related to lateral magma migration to the south-west, exploiting regional tectonic stress regimes, towards eruption vents within the caldera. 3D gravity inversion, including models numerically constrained by a 3D magnetotelluric model, suggest a caldera depth of 5000 ± 500 m that accumulated over multiple collapse episodes along with rifting induced subsidence in the past 550 ka.Our multiphysics approach to investigating caldera structure has revealed buried structural margins and their relationships to eruptive vents and hydrothermal features at the OVC. Detailed geophysical models of caldera structure are rare globally, and our findings are consistent with analogue and numerical models of caldera formation that accompanies the most violent volcanic eruptions on Earth.

The influence of back-arc extension direction on the strain partitioning associated with continental indentation: Analogue modelling and implications for the Circum-Moesian Fault System of South-Eastern Europe

Continental indentation is associated with deformation transfer from shortening to strike-slip faulting and is often affected by subduction related processes such as slab roll-back driven back-arc extension. We use crustal-scale analogue modelling to investigate the effects of extension direction on the strain partitioning and deformation transfer during indentation. The modelling results show that extension parallel to the strike-slip margin of the indenter creates subsidence distributed in several areas which may connect to form a large sedimentary basin behind the indenter. This transtensional basin with v-shape geometry narrows gradually towards the strike-slip margin of the indenter. In contrast, models with extension perpendicular to the strike-slip margin distributes transtensional deformation away from the indenter. Our results are in good correlation with the evolution of the Carpatho-Balkanides orocline of South-Eastern Europe, where the Circum-Moesian Fault System accommodates oroclinal bending during indentation against the Moesian Platform. In this area, the modelling explains the coeval and contrasting extensional features observed along the strike-slip margin and behind the indenter (i.e. the Getic Depression and the Morava Valley Corridor), driven by the roll-back of the Carpathian embayment and Adriatic slabs.

Timescales of subduction initiation and evolution of subduction thermal regimes

Subduction zones are first-order features of plate tectonics on Earth, yet the mechanisms by which subduction initiates remain enigmatic and controversial. Here, we reappraise the timing of metamorphism of the rock units first detached from the leading edge of the downgoing slab during initiation of the Neotethys subduction, now preserved in the metamorphic sole of the Semail ophiolite (Oman–United Arab Emirates). Using petrochronology and phase equilibrium modeling, we demonstrate that subduction initiated prior to 102–100 Ma at a slow rate (< 1 cm/yr). Subduction stagnated at relatively warm conditions (15–20°C/km) for > 5 Myr before evolving into a faster (≥ 2–5 cm/yr) and colder (∼7°C/km) self-sustained regime. Subduction acceleration (i.e. “unlocking” stage) triggered the onset of slab retreat, large-scale corner flow and fast ocean spreading in the overriding plate at 96–95 Ma, through the progressive change of thermo-mechanical structure of the plate interface. This study reconciles conflicting analogue and numerical subduction initiation models, shedding light on the thermal, mechanical and kinematic complexity of subduction initiation.

Gravitational analog of Faraday rotation in the magnetized Kerr and Reissner-Nordström spacetimes

It is known that the gravitational analog of the Faraday rotation arises in the rotating spacetime due to the nonzero gravitomagnetic field. In this paper, we show that it also arises in the "nonrotating" Reissner-Nordstr\"om spacetime, if it is immersed in a uniform magnetic field. The non-zero angular momentum (due to the presence of electric charge and magnetic field) of the electromagnetic field acts as the twist potential to raise the gravitational Faraday rotation as well as the gravitational Stern-Gerlach effect in the said spacetimes. The twisting can still exist even if the mass of the spacetime vanishes. In other words, the massless charged particle(s) immersed in a uniform magnetic field are able to twist the spacetime in principle, and responsible for the rotation of the plane of polarization of light. This, in fact, could have applications in the basic physics and the analog models of gravity. Here, we also study the effect of magnetic fields in the Kerr and Reissner-Nordstr\"om spacetimes, and we derive the exact expressions for the gravitational Faraday rotation and the gravitational Stern-Gerlach effect in the magnetized Kerr and Reissner-Nordstr\"om spacetimes. Calculating the lowest order of the gravitational Faraday effect arisen due to the presence of a magnetic field, we show that the logarithm correction of the distance of the source and observer in the gravitational Faraday rotation and gravitational Stern-Gerlach effect for the said spacetimes is an important consequence of the presence of the magnetic field. From the astrophysical point of view, our result could be helpful to study the effects of (gravito)magnetic fields on the propagation of polarized photons in the strong gravity regime of the collapsed object.

Mechanisms for the Generation of Complex Fracture Networks: Observations From Slant Core, Analog Models, and Outcrop

We use observations of hydraulic fractures in core, outcrop attributes of natural hydraulic fractures, and analogue models, to address how hydraulic fracture networks evolve. A slant core from the Wolfcamp Formation—an unconventional shale hydrocarbon reservoir in the Permian Basin of West Texas—collected within 18 m and 30 m of two hydraulically stimulated horizontal wells, provided an opportunity to examine hydraulic fractures directly. In approximately 183 m of core, 309 calcite-sealed natural opening-mode fractures and 375 hydraulic fractures were identified. Many hydraulic fractures in the core show complex morphology, including twist-hackle segmentation, diversion, and bifurcation; these structures most commonly develop at lithological bed boundaries and mechanical heterogeneities such as natural fractures and concretions. An outcrop of bed-parallel pavements in the Cretaceous Boquillas Formation in West Texas contains opening-mode fractures that likely formed by natural hydraulic fracturing. Fracture traces provide evidence of twist-hackle segmentation, and are typically associated with bed boundaries and preexisting bed-parallel stylolites. A laboratory study of hydraulic fracturing of 33 synthetic blocks of gypsum and hydrostone revealed fracture steps, diversions, twist hackles, and multiple overlapping fractures together with information on fracture growth directions. These complexities in the fracture network were dominantly nucleated at inclusions used to simulate pre-existing fractures, and as a result of mechanical heterogeneity introduced by the wellbore and perforations. Collectively, our results show that complex fracture networks are produced in hydraulic fracturing of self-sourced reservoir strata. Mechanical stratigraphic boundaries and other heterogeneities are likely to enhance fracture network complexity through the processes of segmentation, diversion, and bifurcation. These processes create multiple fracture strands, resulting in an increased number of hydraulic fractures over those initiated, thereby increasing total fracture surface area. Our study provides insight into hydraulic fracture network propagation, and has applications for evaluation, completion, production, and fracture modeling of unconventional reservoirs.

Application of The Classical Soliton Theory to Study the Dynamics in PassiveDispersed and Active-Relaxation Media During the Formation of a Twist in A Toroidal Plasma

In this paper we consider the possibility of using analog models to study the behavior of the evolution and dynamics of toroidal vortex flows. The current model based on coupled van der Pol generators is used as the main one. In this robot, based on nonlinear dynamics display Bernoulli presented the evolution of the Torus. The use of analog models makes it possible to trace the dynamics of vortex flows. In General, the presented results allow us to confidently assert that both in the experiment and in the theoretical consideration we are dealing with the same object - a strange attractor of the Smale – Williams type in a non-Autonomous oscillatory system. The available data suggest that it is an attractor of hyperbolic type, although, strictly speaking, this statement needs mathematical proof. The appearance of an example of a physical system with a hyperbolic chaotic attractor is of fundamental importance for the further development of nonlinear dynamics and its applications. This is, in a sense, a "breakthrough into the hyperbolic realm." Based on the inherent property of coarseness of hyperbolic attractors, we can build other examples of systems with hyperbolic chaos. The presence of such physical systems opens up opportunities for the application of a deeply studied branch of mathematics – hyperbolic theory, and also translates into practice the problem of comparative study of hyperbolic and non-hyperbolic chaos in theory and experiment. This system can be used to study toroidal vortex processes.

Modelling the 4D kinematics of extensional structures developed above discontinuous inclined ductile basal detachments

A series of scaled analogue models were used to a preliminary study on the influence of the basal detachment configuration on the evolution of extensional systems, developed above an inclined basal ductile detachment. Three different basal configurations were aimed to test extension above: i) a homogeneously distributed ductile detachment; ii) two sectors with a different distribution of the ductile detachment, separated by an abrupt, transversal boundary; ii) a laterally variable width of the ductile detachment, driven by an abrupt oblique boundary. Fault activity was monitored through a series of digital elevation models obtained from the laser scanning of the models' surface. Results of the models analysis show how the geometry, the distribution, the kinematic, and the timing of faulting is strongly controlled by the geometry and orientation of the ductile-brittle interface in respect to the extension direction. Faults close to the brittle-ductile interface develop following the interface geometry, whose effect is reduced moving away from it. In addition, we observe a major number of faults which accommodates lower amount of extension and are less closely spaced above longer ductile detachments. Our results can be compared with natural case-histories along continental passive margins, where extension occurs above a dipping salt detachment, with inhomogeneous distribution (e.g., the northern Gulf of Mexico, central Brazilian margin, Angola margin).

The rheology and deformation of the South Tibetan Detachment System as exposed at Zherger La, east-central Himalaya: Implications for exhumation of the Himalayan metamorphic core

Deformation processes and rheological changes within the South Tibetan Detachment System (STDS) played a key role in accommodating exhumation of the Greater Himalayan Sequence (GHS). We present a study for the STDS in Zherger La, Yadong region, east-central Himalaya, to better quantify the spatial and temporal variations of the shear zone's internal deformation and rheology properties. Quartz microstructures and crystallographic preferred orientations, together with quantitative estimates of deformation temperatures, differential stresses, strain rates and viscosities are deduced from the ductile segment of the detachment zone. The mylonites that comprise the exposed shear zone preserve a range of deformation conditions that are interpreted in terms of progressive exhumation. Strain localization within the STDS is indicated by the microstructural evolution from penetrative deformation of constitutive minerals to localized deformation into quartz, which exhibit interconnected networks and high strain zones. Deformation temperatures decrease from 510 ± 40 to 405 ± 50 °C and differential stresses increase from 24 to 100 MPa structurally upwards, as indicated by two-feldspar thermometry and quartz paleopiezometry, respectively. Strain rates derived from quartz dislocation creep flow law are on the order of 10−12-10−13 s−1 and are broadly consistent with macrostructurally-derived strain rates of 1.8–5.1 × 10−13 s−1, which are calculated from previously determined exhumation rates and shear zone width. The estimated differential stresses and strain rates are further utilized to determine the variation of viscosities across the STDS. The viscosities within the STDS range at 1019–1020 Pa s. In conjunction with the published numerical modelling and analog modeling studies, the estimated viscosity data are compatible with the channel flow model for exhumation.

Relationship Between Lateral/Basal Shear Stress Ratio and Structural Vergence of Thrust Wedges: Results From Analogue Modeling and Implications for the Origin of Eastern Sichuan–Xuefeng Fold‐Thrust Belt in South China

AbstractThrust wedges are common in nature, but not all of their origins can be properly explained by the classic Coulomb wedge theory, which considers only a 2D perspective. A few analogue models, however, revealed that lateral shear stress (inherent in both analogue models and nature) may strongly affect the development of thrust wedges and the lateral/basal shear stress (τs/τd) ratio might have controlled the structural vergence of thrust wedge, suggesting that origin of thrust wedges needs to be considered from a 3D perspective. The origin of the Eastern Sichuan–Xuefeng fold‐thrust belt (ESXFTB), which is characterized by two oppositely vergent thrust systems at different crustal levels and may contain another large purely backward‐vergent thrust wedge on the world, is still problematic. Revealing the relationship between τs/τd ratio and structural vergence may prompt a deep understanding of the origin of thrust wedges as well as the ESXFTB. This relationship, however, is still not very clear due to the lack of systematic experiments. For these reasons, we performed systematic experiments of two types of analogue models under different τs/τd ratios. Our model results revealed, for the first time, that structural vergence of thrust wedges lying on a weak décollement may progressively change from frontward (when τs/τd &lt;0.09) to dual (when τs/τd = 0.09–1.15) and then to backward (when τs/τd &gt;1.15) and the two oppositely vergent thrust systems in the ESXFTB can be produced simultaneously by the single northwestward Mesozoic shortening probably due to their apparently different τs/τd ratios.

Analogue Models and Universal Machines. Paradigms of Epistemic Transparency in Artificial Intelligence

The problem of epistemic opacity in Artificial Intelligence (AI) is often characterised as a problem of intransparent algorithms that give rise to intransparent models. However, the degrees of transparency of an AI model should not be taken as an absolute measure of the properties of its algorithms but of the model’s degree of intelligibility to human users. Its epistemically relevant elements are to be specified on various levels above and beyond the computational one. In order to elucidate this claim, I first contrast computer models and their claims to algorithm-based universality with cybernetics-style analogue models and their claims to structural isomorphism between elements of model and target system (in: Black, Models and metaphors, 1962). While analogue models aim at perceptually or conceptually accessible model-target relations, computer models give rise to a specific kind of underdetermination in these relations that needs to be addressed in specific ways. I then undertake a comparison between two contemporary AI approaches that, although related, distinctly align with the above modelling paradigms and represent distinct strategies towards model intelligibility: Deep Neural Networks and Predictive Processing. I conclude that their respective degrees of epistemic transparency primarily depend on the underlying purposes of modelling, not on their computational properties.

Foamquake: A Novel Analog Model Mimicking Megathrust Seismic Cycles

AbstractIn the last decades, seismotectonic analog models have been developed to better understand many aspects of the seismic cycle. Differently from other lab‐quake experiments, seismotectonic models mimic the first order characteristics of the seismic cycle in a scaled fashion. Here we introduce Foamquake: A novel seismotectonic model with a granular frictional interface that as a whole behaves elastoplastically. The model experiences cycles of elastic loading and release via spontaneous nucleation of frictional instabilities at the base of an elastic foam wedge, hereafter called foamquakes. These analog earthquakes show source parameters (i.e., moment‐duration and moment‐rupture area) scaling as great interplate earthquakes and a coseismic displacement of few tens of meters when scaled to nature. Models with two asperities separated by a barrier can be performed with Foamquake given the 3D nature of the setup. Such model configuration generates sequences of full and partial ruptures with different recurrence intervals as well as rupture cascades. By tuning the normal load acting on individual asperities, Foamquake reproduces superimposed cycles rupture patterns such as those observed along natural megathrusts. The physical properties of asperities and barriers affect model seismic behavior. Asperities with similar properties and low yield strength fail preferentially in a simultaneous manner. The combination of all those characteristics suggests that Foamquake is a valuable tool for investigating megathrust seismicity and seismic processes that depend on the 3D nature of the subduction environment.

Hanging-wall deformation at the active Sierra Palomera extensional fault (Jiloca basin, Spain) from structural, morphotectonic, geophysical and trench study

The NNW-SSE trending Sierra Palomera fault is characterized as an active, nearly pure extensional fault with mean transport direction towards N230°E, consistent with the ENE-WSW extension trajectories of the recent to present-day regional stress field. Its macrostructure is described from surface geology and magnetometric and electromagnetic surveys, which have allowed identifying two subsidiary, nearly parallel normal faults (antithetic and synthetic, respectively). The structural contour map of an extensive planation surface, dated to 3.8 Ma, provides a maximum fault throw s.s. of 330 m for the main fault (480 m including bending), and a net slip rate of 0.09–0.10 mm/a (0.13–0.15 mm/a including bending). Trench study focussed on the subsidiary antithetic fault shows evidence of its activity during Middle-Late Pleistocene times, offsetting ca. 2.5 m the slope of a well-preserved alluvial fan. Detailed analysis and retrodeformation of the antithetic fault and other minor ruptures in the trench has allowed defining seven deformation events. The lack of a consistent age model for the involved sedimentary sequence makes them almost meaningless in terms of paleoseismic history. However, geometry and sequential development of meso-scale faults (intermediate between seismic-scale and analogue models) allows unravelling the extensional deformation history within the hanging-wall block of the Sierra Palomera fault. Progressive rupture patterns reveal shifting from dominantly synthetic to dominantly antithetic faulting, suggesting both kinematical control linked to rollover growth, and dynamical control by the regional stress field.

Participatory Modeling: A Methodology for Engaging Stakeholder Knowledge and Participation in Social Science Research

Participatory modeling (PM) is an engaged research methodology for creating analog or computer-based models of complex systems, such as socio–environmental systems. Used across a range of fields, PM centers stakeholder knowledge and participation to create more internally valid models that can inform policy and increase engagement and trust between communities and research teams. The PM process also presents opportunities for knowledge co-production and eliciting cross-sectional and longitudinal data on stakeholders’ worldviews and knowledge, risk assessment, decision-making, and social learning. We present an overview of the stages for PM and how it can be used for community-based, stakeholder-engaged social science research.

Sediment Recycling and the Evolution of Analog Orogenic Wedges

AbstractIn convergent systems, the interplay between tectonics, erosion, and sedimentation controls the orogenic evolution. The nature of the interactions between these factors is still elusive due to the complex feedbacks that operate across different temporal and spatial scales. Here, we investigate these feedbacks with analog models of landscape evolution designed to account for both tectonic forcing and surface processes, using a water‐saturated granular material that allows to simulate contemporary brittle deformation and surface processes. The deformation is imposed by the movement of a rigid backstop, and surface processes are triggered by simulated rainfall and runoff. We vary the convergence velocity, rainfall rate, and basal angle of the box, testing how different boundary conditions affect the balance between tectonics and surface processes. We measure the competition between input fluxes (tectonics) and output fluxes (erosion) of material, showing how sedimentation strongly affects the balance between these fluxes. The results suggest that the experimental equilibrium between tectonics and erosion can be achieved, in the analog models, only for low convergence rates (about 10 mm hr−1) and/or for high basal angle (&gt;2°, limited sedimentation). If the foreland is overfilled with sediments and/or if convergence velocity is higher, channels decrease their erosional efficiency, moving the dynamic equilibrium between tectonics and erosion toward the former.

Overriding Plate Deformation and Topography During Slab Rollback and Slab Rollover: Insights From Subduction Experiments

AbstractSome subduction zones in nature show mainly overriding plate (OP) extension and low topography, and others show mainly shortening and elevated topography. Here we investigate how end‐member subduction modes (trench retreat with slab rollback and trench advance with slab rollover) affect overriding plate deformation (OPD), topography, and mantle flow with time‐evolving three‐dimensional fully‐dynamic analog models using particle image velocimetry. We conduct two sets of experiments, one of which is characterized by trench retreat, and the other characterized by trench advance. Experiments showing continuous trench retreat experience overall OP extension, while experiments dominated by trench advance experience overall shortening. Both subduction modes present fore‐arc shortening and intra‐arc extension. Our experiments indicate that the overall OPD is mainly driven by the horizontal mantle flow at the base of the OP inducing a viscous drag force (FD), and is determined by the horizontal gradient of the horizontal mantle shear rate , which controls the horizontal trench‐normal gradient in FD. Furthermore, a large‐scale trenchward OP tilting and overall subsidence are observed in the experiments showing continuous trench retreat, while a landward OP tilting and an overall uplift are observed during long‐term trench advance. The two types of topography during the two different subduction modes can be ascribed to the downward component of the large‐scale trenchward mantle flow and the upward component of the landward mantle flow, respectively, and thus represent forms of dynamic topography. Our models showing trench advance provide a possible mechanism for OPD and topography at the Makran subduction zone.

Explaining Structural Difference Between the Eastern and Western Zones of the Qiongdongnan Basin, Northern South China Sea: Insights From Scaled Physical Models

AbstractThe western and eastern zones of the Qiongdongnan Basin (China) show clear contrasts in sub‐basin distribution, fault orientation, and structural styles. Generally, pre‐existing structures are considered to control such differences, that is, NE‐striking main faults in the western zone underwent orthogonal stretching, while E–W‐ and NE‐striking faults in the eastern zone underwent oblique stretching. In addition to the influence of the pre‐existing structures, we suggest that depth‐dependent stretching controlled by the strength of the lower crust together with a change in extension direction may also affect the structural differences of the western and eastern Qiongdongnan Basin. In this study, we use physical analog modeling to explain the structural differences between the eastern and western zones of the Qiongdongnan Basin with the main variables being the strength of the lower crust and a change in extension direction. The model with weak lower crust is successful in accounting for the observed first‐order structural characteristics of this basin. This finding indicates that the rift formation is depth‐dependent and controlled by the orientation of the velocity discontinuities (VDs) and thus the extension direction. Experiment with a change of the extensional direction and weak lower crust reveal that the pre‐existing VDs mainly control the structural belts’ location and fault strikes; some minor structures (late features) respond to the extension change, whereas the main faults are inherited and developed from the previous stage of deformation.

Is the Anti-Atlas of Morocco still uplifting?

Topographic elevation of orogenic belts in the results of several processes and contributions occurring at different temporal and spatial scales, from short-to long-term and from the surface up to the mantle. Disentangle surface evolution on key areas may then encode for deeper ongoing processes. In this concern, the Anti Atlas of Morocco is a prominent mountain belt with moderate relief and with a long deformation history not recorded during the Cenozoic. The modern topography of the Anti-Atlas is resulted from late Miocene uplift driven by mantle processes. In this study, we address the question if mantle processes are still affecting the topography of the Anti-Atlas by providing new clues on the late Miocene-Quaternary uplift history of the north-western margin of the mountain belt.We analyze and compare the river long profiles and related morphometric features of channels draining the Souss Basin of the Anti-Atlas in western Morocco with analog and numeric similar scenarios. We find that the steepness of the rivers, the χ, ksn, slope and local relief show limited values. Moreover, the channels are characterized by Quaternary fluvial conglomerates lying at high elevation. The projection of the non-re-equilibrated river profile runs below the lower part of the channel. We explore the mechanism that could produce this feature by both numerical and analog models. The analogue and numerical long river profiles from modeling show similar morphometric features compared to the natural case when the uplift rate is diminished or set to zero. We speculate that in the Anti Atlas, uplift may have waned over Quaternary time leading to a spatial change in the critical point of sedimentation, triggering valley infilling at high elevation, and in turn a slow burying of the Anti-Atlas.