A new experimental approach to assess the influence of gravity gliding on salt tectonics in rift basins

2021 ◽  
Author(s):  
Michael Warsitzka ◽  
Prokop Závada ◽  
Fabian Jähne-Klingberg ◽  
Piotr Krzywiec
Keyword(s):  
Cross Sections ◽  
Hanging Wall ◽  
Fault Zones ◽  
Image Correlation ◽  
Salt Tectonics ◽  
Correlation Technique ◽  
Shear Stresses ◽  
Rift Basins ◽  
Salt Flow ◽  
Extensional Structures

<p>Salt flow in rift basins is mainly driven by sub- and supra-salt extension imposing shear stresses and differential loading on the salt layer. In many rift basins, the graben flanks are tilted as a result of thermal subsidence and sediment load. Such tilt induces additional basin-ward directed stresses potentially causing downward directed salt flow and gravity gliding of the supra-salt overburden. However, sediment loading in extensional basins is usually largest in the basin centre, which would lead to an upward directed salt expulsion and might act as an effective buttress resisting downward gliding.</p><p>Our aim is to investigate the opposing influence of sub-salt extension, sedimentary loading and tilting on deformation patterns in the viscous salt and the brittle overburden. We try to assess under which geological configurations (e.g. minimum basin slope or topographic gradient) upward directed salt flow and downward directed gravity gliding are the dominating deformation processes in extensional basins. Therefore, we developed a new analogue modelling apparatus enabling to simulate the processes of tectonic extension of a graben structure and the gradual tilting of the graben flanks, acting either simultaneously or separately. Using digital image correlation technique, temporal and spatial changes of the displacement and strain patterns can be analysed. Cross sections through the final experiments enable to identify structures characteristic for specific driving processes.</p><p>Here, we present results of a preliminary experimental study in which the basic influence of flank tilting and syn-kinematic sedimentation on salt tectonics in rift basins is examined. In case that the graben flanks remain flat during extension, widespread extensional fault zones develop on the footwall sides near the graben faults. In case that the flanks are tilted simultaneously with basal extension, additional extensional fault zones evolve at the upslope basin margins resulting from downward gliding of the overburden. In the downslope basin centre, this peripheral extension is balanced by reduced amounts of extension near the graben and later by shortening above the graben bounding faults and the hanging wall graben centre. If syn-kinematic sedimentation is introduced, downslope gravity gliding is significantly reduced and extensional fault zones are rather localized. Peripheral extensional structures observed in the experiments resemble typical thin-skinned extensional structures occurring at the flanks of many salt-bearing rift basins, e.g. the Polish Basin and Norwegian-Danish Basin. Thus, such structures might serve as diagnostic indicators for the occurrence of gravity gliding in rift basins.</p>

scholarly journals Contribution of gravity gliding in salt-bearing rift basins – a new experimental setup for simulating salt tectonics under the influence of sub-salt extension and tilting

Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1987-2020
Author(s):  
Michael Warsitzka ◽  
Prokop Závada ◽  
Fabian Jähne-Klingberg ◽  
Piotr Krzywiec
Keyword(s):  
Structural Evolution ◽  
Image Correlation ◽  
Salt Tectonics ◽  
Rift Basins ◽  
Downward Movement ◽  
Basin Scale ◽  
Experimental Analogue ◽  
Pure Extension ◽  
Top View ◽  
Salt Flow

Abstract. Basin-scale salt flow and the evolution of salt structures in rift basins is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward-directed driver for salt tectonics. We designed a new experimental analogue apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup, demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting, and extension combined with tilting. Digital image correlation of top-view stereoscopic images was applied to reveal the 3D displacement and strain patterns. The results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement; i.e. the amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional faults developed as a result of gravity gliding. A comparison with natural examples reveals that such fault zones can also be observed at the margins of many salt-bearing rift basins indicating that gravity gliding played a role in these basins.

scholarly journals Contribution of gravity gliding in salt-bearing rift basins – A new experimental setup for simulating salt tectonics under the influence of sub-salt extension and tilting

2021 ◽  
Author(s):  
Michael Warsitzka ◽  
Prokop Závada ◽  
Fabian Jähne-Klingberg ◽  
Piotr Krzywiec
Keyword(s):  
Structural Evolution ◽  
Image Correlation ◽  
Salt Tectonics ◽  
Rift Basins ◽  
Downward Movement ◽  
Experimental Procedure ◽  
Basin Scale ◽  
Pure Extension ◽  
Top View ◽  
Salt Flow

Abstract. Basin-scale salt flow and the evolution of salt structures in rift basin is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward directed driver for salt tectonics. We designed a new experimental analog apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting and extension combined with tilting. Digital image correlation of top view stereoscopic images was applied to reveal the 3D displacement and strain patterns. Results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement, i.e. amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional fault developed, which resemble fault zones observed on basin flanks offset from the central graben zone.

scholarly journals Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
A. Mujdeci ◽  
D. V. Bompa ◽  
A. Y. Elghazouli
Keyword(s):  
Axial Compression ◽  
Cross Section ◽  
Cross Sections ◽  
Image Correlation ◽  
Combined Loading ◽  
Test Results ◽  
Compression Tests ◽  
Confinement Effects ◽  
Rubber Content ◽  
Dependent Modification

AbstractThis paper describes an experimental investigation into confinement effects provided by circular tubular sections to rubberised concrete materials under combined loading. The tests include specimens with 0%, 30% and 60% rubber replacement of mineral aggregates by volume. After describing the experimental arrangements and specimen details, the results of bending and eccentric compression tests are presented, together with complementary axial compression tests on stub-column samples. Tests on hollow steel specimens are also included for comparison purposes. Particular focus is given to assessing the confinement effects in the infill concrete as well as their influence on the axial–bending cross-section strength interaction. The results show that whilst the capacity is reduced with the increase in the rubber replacement ratio, an enhanced confinement action is obtained for high rubber content concrete compared with conventional materials. Test measurements by means of digital image correlation techniques show that the confinement in axial compression and the neutral axis position under combined loading depend on the rubber content. Analytical procedures for determining the capacity of rubberised concrete infilled cross-sections are also considered based on the test results as well as those from a collated database and then compared with available recommendations. Rubber content-dependent modification factors are proposed to provide more realistic representations of the axial and flexural cross-section capacities. The test results and observations are used, in conjunction with a number of analytical assessments, to highlight the main parameters influencing the behaviour and to propose simplified expressions for determining the cross-section strength under combined compression and bending.

Triassic-age salt tectonics of the Central North Sea

2014 ◽  
Vol 2 (4) ◽  
pp. SM19-SM28 ◽  
Author(s):  
John F. Karlo ◽  
Frans S. P. van Buchem ◽  
Jan Moen ◽  
Katie Milroy
Keyword(s):  
North Sea ◽  
Lateral Displacement ◽  
Salt Tectonics ◽  
Structural Relief ◽  
Tectonic Style ◽  
Thermal Doming ◽  
Central North Sea ◽  
Extensional Structures

The framework of salt tectonics in the Central North Sea was set early in the Triassic. We defined and illustrated five major domains of differing salt tectonic style. The differing structural styles were all interpreted as having evolved under a component of lateral displacement pairing extensional and contractional structures, produced by some combination of decoupled rift extension and gravity sliding. However, the extensional structures are located toward the basin center and the contractional structures near the original updip limits of salt. This suggests a framework driven by gravity sliding of the sediments overlying the Zechstein away from the Central Graben. Possible mechanisms for structural relief away from the Central Graben are the Triassic focus of rifting lying further east at the Norwegian-Danish basin, footwall uplift of a Triassic Central Graben precursor and significant thermal doming occurring much earlier than had previously been thought. The mechanisms are not mutually exclusive and may have acted in concert.

Stress concentration factors for the torsion of curved beams of arbitrary cross-section

2006 ◽  
Vol 220 (12) ◽  
pp. 1709-1726 ◽  
Author(s):  
R E Cornwell
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Cross Section ◽  
Cross Sections ◽  
Shear Stresses ◽  
Curved Beams ◽  
Finite Element Implementation ◽  
Out Of Plane ◽  
Concentration Factors ◽  
Stress Concentration Factors

There are numerous situations in machine component design in which curved beams with cross-sections of arbitrary geometry are loaded in the plane of curvature, i.e. in flexure. However, there is little guidance in the technical literature concerning how the shear stresses resulting from out-of-plane loading of these same components are effected by the component's curvature. The current literature on out-of-plane loading of curved members relates almost exclusively to the circular and rectangular cross-sections used in springs. This article extends the range of applicability of stress concentration factors for curved beams with circular and rectangular cross-sections and greatly expands the types of cross-sections for which stress concentration factors are available. Wahl's stress concentration factor for circular cross-sections, usually assumed only valid for spring indices above 3.0, is shown to be applicable for spring indices as low as 1.2. The theory applicable to the torsion of curved beams and its finite-element implementation are outlined. Results developed using the finite-element implementation agree with previously available data for circular and rectangular cross-sections while providing stress concentration factors for a wider variety of cross-section geometries and spring indices.

Using bedrock thermochronometer systems to constrain fold-thrust belt geometry and kinematics, insight from the eastern Himalayas, Arunachal Pradesh, India.

2021 ◽  
Author(s):  
Nadine McQuarrie ◽  
Mary Braza
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Hanging Wall ◽  
Vertical Component ◽  
Eastern Himalaya ◽  
Thrust Belt ◽  
Arunachal Pradesh ◽  
Eastern Himalayas ◽  
Cross Section Geometry ◽  
Geometry And Kinematics

<div> <p>One of the first order questions regarding a cross-section representation through a fold-thrust belt (FTB) is usually “how unique is this geometrical interpretation of the subsurface?”  The proposed geometry influences perceptions of inherited structures, decollement horizons, and both rheological and kinematic behavior.  Balanced cross sections were developed as a tool to produce more accurate and thus more predictive geological cross sections.  While balanced cross sections provide models of subsurface geometry that can reproduce the mapped surface geology, they are non-unique, opening the possibility that different geometries and kinematics may be able to satisfy the same set of observations. The most non-unique aspects of cross sections are: (1) the geometry of structures that is not seen at the surface, and (2) the sequence of thrust faulting.  We posit that integrating sequentially restored cross sections with thermokinematic models that calculate the resulting subsurface thermal field and predicted cooling ages of rocks at the surface provides a valuable means to assess the viability of proposed geometry and kinematics.  Mineral cooling ages in compressional settings are the outcome of surface uplift and the resulting focused erosion.  As such they are most sensitive to the vertical component of the kinematic field imparted by ramps and surface breaking faults in sequential reconstructions of FTB.  Because balanced cross sections require that the lengths and locations of hanging-wall and footwall ramps match, they provide a template of the ways in which the location and magnitude of ramps in the basal décollement have evolved with time.  Arunachal Pradesh in the eastern Himalayas is an ideal place to look at the sensitivity of cooling ages to different cross section geometries and kinematic models. Recent studies from this portion of the Himalayan FTB include both a suite of different cross section geometries and a robust bedrock thermochronology dataset. The multiple published cross-sections differ in the details of geometry, implied amounts of shortening, kinematic history, and thus exhumation pathways. Published cooling ages data show older ages (6-10 Ma AFT, 12-14 Ma ZFT) in the frontal portions of the FTB and significantly younger ages (2-5 Ma AFT, 6-8 Ma ZFT) in the hinterland. These ages are best reproduced with kinematic sequence that involves early forward propagation of the FTB from 14-10 Ma.  The early propagation combined with young hinterland cooling ages require several periods of out-of-sequence faulting. Out-of-sequence faults are concentrated in two windows of time (10-8 Ma and 7-5 Ma) that show systematic northward reactivation of faults.  Quantitative integration of cross section geometry, kinematics and cooling ages require notably more complicated kinematic and exhumation pathways than are typically assumed with a simple in-sequence model of cross section deformation.  While also non-unique, the updated cross section geometry and kinematics highlight components of geometry, deformation and exhumation that must be included in any valid cross section model for this portion of the eastern Himalaya.</p> </div>

Predicting strains in embedded reinforcement based on surface deformation obtained by digital image correlation technique

2021 ◽  
Author(s):  
Ali Mirzazade ◽  
Cosmin Popescu ◽  
Thomas Blanksvärd ◽  
Björn Täljsten
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Surface Deformation ◽  
Local Strain ◽  
Surface Strain ◽  
Image Correlation ◽  
Correlation Technique ◽  
Proposed Model ◽  
Structural Inspection ◽  
Semi Empirical

<p>This study is carried out to assess the applicability of using a digital image correlation (DIC) system in structural inspection, leading to deploy innovative instruments for strain/stress estimation along embedded rebars. A semi-empirical equation is proposed to predict the strain in embedded rebars as a function of surface strain in RC members. The proposed equation is validated by monitoring the surface strain in ten concrete tensile members, which are instrumented by strain gauges along the internal steel rebar. One advantage with this proposed model is the possibility to predict the local strain along the rebar, unlike previous models that only monitored average strain on the rebar. The results show the feasibility of strain prediction in embedded reinforcement using surface strain obtained by DIC.</p>

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