scholarly journals Throw variations and strain partitioning associated with fault-bend folding along normal faults

2019 ◽  
Author(s):  
Efstratios Delogkos ◽  
Muhammad Mudasar Saqab ◽  
John J. Walsh ◽  
Vincent Roche ◽  
Conrad Childs
Keyword(s):  
Large Scale ◽  
Full Range ◽  
Quantitative Model ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Fault Surface ◽  
Irregular Geometries ◽  
Surface Irregularities ◽  
Fault Bend ◽  
Constant Displacement

Abstract. Normal faults have irregular geometries on a range of scales arising from different processes including refraction and segmentation. A fault with an average dip and constant displacement on a large-scale, will have irregular geometries on smaller scales, the presence of which will generate fault-related folds, with major implications for across-fault throw variations. A quantitative model has been presented which illustrates the range of deformation arising from movement on fault surface irregularities, with fault-bend folding generating geometries reminiscent of normal drag and reverse drag. The model highlights how along-fault displacements are partitioned between continuous (i.e. folding) and discontinuous (i.e. discrete displacement) strain along fault bends characterised by the full range of fault dip changes. Strain partitioning has a profound effect on measured throw values across faults, if account is not taken of the continuous strains accommodated by folding and bed rotations. We show that fault throw can be subject to errors of up to ca. 50 % for realistic fault bend geometries (up to ca. 40°), even on otherwise sub-planar faults with constant displacement. This effect will provide apparently more irregular variations in throw and bed geometries that must be accounted for in associated kinematic interpretations.

scholarly journals Throw variations and strain partitioning associated with fault-bend folding along normal faults

Solid Earth ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 935-945
Author(s):  
Efstratios Delogkos ◽  
Muhammad Mudasar Saqab ◽  
John J. Walsh ◽  
Vincent Roche ◽  
Conrad Childs
Keyword(s):  
Large Scale ◽  
Full Range ◽  
Quantitative Model ◽  
Normal Faults ◽  
Strain Partitioning ◽  
Potential Significance ◽  
Irregular Geometries ◽  
Fault Bend ◽  
Ca 50 ◽  
Constant Displacement

Abstract. Normal faults have irregular geometries on a range of scales arising from different processes including refraction and segmentation. A fault with constant dip and displacement on a large-scale will have irregular geometries on smaller scales, the presence of which will generate fault-related folds and down-fault variations in throw. A quantitative model is presented which illustrates the deformation arising from movement on irregular fault surfaces, with fault-bend folding generating geometries reminiscent of normal and reverse drag. Calculations based on the model highlight how fault throws are partitioned between continuous (i.e. folding) and discontinuous (i.e. discrete offset) strain along fault bends for the full range of possible fault dip changes. These calculations illustrate the potential significance of strain partitioning on measured fault throw and the potential errors that will arise if account is not taken of the continuous strains accommodated by folding and bed rotations. We show that fault throw can be subject to errors of up to ca. 50 % for realistic down-dip fault bend geometries (up to ca. 40∘), on otherwise sub-planar faults with constant displacement. This effect will provide irregular variations in throw and bed geometries that must be accounted for in associated kinematic interpretations.

Geometrical characterisation of fault arrays in three dimensions

2021 ◽  
Author(s):  
Vincent Roche ◽  
Giovanni Camanni ◽  
Conrad Childs ◽  
Tom Manzocchi ◽  
John Walsh ◽  
...  
Keyword(s):  
Full Range ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Normal Faults ◽  
Fault Geometry ◽  
Surface Geometry ◽  
Fault Surface ◽  
Mechanical Stratigraphy ◽  
Quantitative Basis ◽  
Geometry Analysis

<p>Normal faults are often complex three-dimensional structures comprising multiple sub-parallel segments separated by intact or breached relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution. Relay zones are classified according to whether they step in the strike or dip direction and whether the relay zone-bounding fault segments are unconnected in 3D or bifurcate from a single surface. Complex fault surface geometry is then described in terms of the relative numbers of different types of relay zones to allow comparison of fault geometry between different faults and different geological settings. A large database of 87 fault arrays compiled primarily from mapping 3D seismic reflection surveys and classified according to this scheme, reveals the diversity of 3D fault geometry. Analysis demonstrates that mapped fault geometries depend on geological controls, primarily the heterogeneity of the faulted sequence and the presence of a pre-existing structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy. In addition, mapped segmentation depends on resolution limits and biases in fault mapping from seismic data. In particular, the results suggest that the proportion of bifurcating relay zones increases as data resolution increases. Overall, where a significant number of relay zones are mapped on a single fault, a wide variety of relay zone geometries occurs, demonstrating that individual faults can comprise segments that are both bifurcating and unconnected in three dimensions. Models for the geometrical evolution of fault arrays must therefore account for the full range of relay zone geometries that appears to be a characteristic of all faults.</p>

Strain partitioning around an indenter during oroclinal bending: kinematics of the Circum-Moesian fault system of the Carpatho-Balkanides

2021 ◽  
Author(s):  
Nemanja Krstekanic ◽  
Liviu Matenco ◽  
Uros Stojadinovic ◽  
Ernst Willingshofer ◽  
Marinko Toljić ◽  
...  
Keyword(s):  
Large Scale ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Strain Partitioning ◽  
The South ◽  
The Carpathians ◽  
The North ◽  
Moesian Platform ◽  
Parallel Extension

<p>The Carpatho-Balkanides of south-eastern Europe is a double 180° curved orogenic system. It is comprised of a foreland-convex orocline, situated in the north and east and a backarc-convex orocline situated in the south and west. The southern orocline of the Carpatho-Balkanides orogen formed during the Cretaceous closure of the Alpine Tethys Ocean and collision of the Dacia mega-unit with the Moesian Platform. Following the main orogen-building processes, the Carpathians subduction and Miocene slab retreat in the West and East Carpathians have driven the formation of the backarc-convex oroclinal bending in the south and west. The orocline formed during clockwise rotation of the Dacia mega-unit and coeval docking against the Moesian indenter. This oroclinal bending was associated with a Paleocene-Eocene orogen-parallel extension that exhumed the Danubian nappes of the South Carpathians and with a large late Oligocene – middle Miocene Circum-Moesian fault system that affected the orogenic system surrounding the Moesian Platform along its southern, western and northern margins. This fault system is composed of various segments that have different and contrasting types of kinematics, which often formed coevally, indicating a large degree of strain partitioning during oroclinal bending. It includes the curved Cerna and Timok faults that cumulate up to 100 km of dextral offset, the lower offset Sokobanja-Zvonce and Rtanj-Pirot dextral strike-slip faults, associated with orogen parallel extension that controls numerous intra-montane basins and thrusting of the western Balkans units over the Moesian Platform. We have performed a field structural study in order to understand the mechanisms of deformation transfer and strain partitioning around the Moesian indenter during oroclinal bending by focusing on kinematics and geometry of large-scale faults within the Circum-Moesian fault system.</p><p>Our structural analysis shows that the major strike-slip faults are composed of multi-strand geometries associated with significant strain partitioning within tens to hundreds of metres wide deformation zones. Kinematics of the Circum-Moesian fault system changes from transtensional in the north, where the formation of numerous basins is controlled by the Cerna or Timok faults, to strike-slip and transpression in the south, where transcurrent offsets are gradually transferred to thrusting in the Balkanides. The characteristic feature of the whole system is splaying of major faults to facilitate movements around the Moesian indenter. Splaying towards the east connects the Circum-Moesian fault system with deformation observed in the Getic Depression in front of the South Carpathians, while in the south-west the Sokobanja-Zvonce and Rtanj-Pirot faults splay off the Timok Fault. These two faults are connected by coeval E-W oriented normal faults that control several intra-montane basins and accommodate orogen-parallel extension. We infer that all these deformations are driven by the roll-back of the Carpathians slab that exerts a northward pull on the upper Dacia plate in the Serbian Carpathians. However, the variability in deformation styles is controlled by geometry of the Moesian indenter and the distance to Moesia, as the rotation and northward displacements increase gradually to the north and west.</p>

The three-dimensional geometries of segmented normal faults

2020 ◽  
Author(s):  
John Walsh ◽  
Vincent Roche ◽  
Giovanni Camanni ◽  
Conrad Childs ◽  
Tom Manzocchi ◽  
...  
Keyword(s):  
Full Range ◽  
Three Dimensional ◽  
Normal Faults ◽  
Basement Structure ◽  
Mechanical Heterogeneity ◽  
Fault Surface ◽  
Mechanical Stratigraphy ◽  
Data Resolution ◽  
3D Geometry ◽  
Quantitative Basis

<p>Normal faults are often complex three dimensional structures comprising multiple sub-parallel segments separated by intervening relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution.</p><p>Individual relay zones can be assigned to one of four types according to their form (i.e. whether the bounding segments are unconnected in 3D or merge into a single surface) and their orientation (i.e. whether they are slip-parallel or slip-perpendicular). From the detailed analysis of 84 fault arrays mapped from 3D seismic reflection surveys (including 63 from our mapping of 8 different study areas and 21 derived from the literature), we show that the 3D geometry of fault arrays can be quantitatively defined on the basis of the relative numbers of these types of relay zones.</p><p>Detailed mapping of fault zones indicates that whilst they can individually contain all four types of relay zone, their relative proportions varies between different study areas. Differences in the proportions of relay zone types are attributed to two primary controls, the mechanical heterogeneity of the faulted sequence and the presence of basement structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy. </p><p>Fault arrays in the literature generally do not contain the full range of possible relay zone type but tend to comprise either all bifurcating relay zones or all unconnected relay zones. These end-member fault geometries have led to contrasting conceptual models for the growth of faults. The mapping conducted here suggests that the proportion of bifurcating relay zones increases as data resolution increases and that fault surface bifurcation is ubiquitous. Models for the geometrical evolution of fault arrays must account for the full range of relay zone geometries that appears to be a characteristic of all faults.</p>

scholarly journals Linked thick- to thin-skinned inversion in the central Kirthar Fold Belt of Pakistan

Solid Earth ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 425-446 ◽  
Author(s):  
Ralph Hinsch ◽  
Chloé Asmar ◽  
Muhammad Nasim ◽  
Muhammad Asif Abbas ◽  
Shaista Sultan
Keyword(s):  
Structural Control ◽  
Large Scale ◽  
Sedimentary Cover ◽  
Motion Vector ◽  
Focal Mechanisms ◽  
Plate Motion ◽  
Normal Faults ◽  
Accretionary Wedge ◽  
Strain Partitioning ◽  
Fold Belt

Abstract. The Kirthar Fold Belt is part of the transpressive transfer zone in Pakistan linking the Makran accretionary wedge with the Himalaya orogeny. The region is deforming very obliquely, nearly parallel to the regional S–N plate motion vector, indicating strong strain partitioning. In the central Kirthar Fold Belt, folds trend roughly N–S and their structural control is poorly understood. In this study, we use newly acquired 2-D seismic data with pre-stack depth migration, published focal mechanisms, surface and subsurface geological data, and structural modelling with restoration and balancing to constrain the structural architecture and kinematics of the Kirthar Fold Belt. The central Kirthar Fold Belt is controlled by Pliocene to recent linked thick-skinned to thin-skinned deformation. The thick-skinned faults are most likely partially inverting rift-related normal faults. Focal mechanisms indicate dip-slip faulting on roughly N–S-trending faults with some dip angles exceeding 40∘, which are considered too steep for newly initiated thrust faults. The hinterland of the study area is primarily dominated by strike-slip faulting. The inverting faults do not break straight through the thick sedimentary column of the post-rift and flexural foreland; rather, the inversion movements link with a series of detachment horizons in the sedimentary cover. Large-scale folding and layer-parallel shortening has been observed in the northern study area. In the southern study area progressive imbrication of the former footwall of the normal fault is inferred. Due to the presence of a thick incompetent upper unit (Eocene Ghazij shales) these imbricates develop as passive roof duplexes. In both sectors the youngest footwall shortcut links with a major detachment and the deformation propagates to the deformation front, forming a large fault-propagation fold. Shortening within the studied sections is calculated to be 18 %–20 %. The central Kirthar Fold Belt is a genuine example of a hybrid thick- and thin-skinned system in which the paleogeography controls the deformation. The locations and sizes of the former rift faults control the location and orientation of the major folds. The complex tectonostratigraphy (rift, post-rift, flexural foreland) and strong E–W gradients define the mechanical stratigraphy, which in turn controls the complex thin-skinned deformation.

scholarly journals Mantle-derived helium released through the Japan trench bend-faults

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jin-Oh Park ◽  
Naoto Takahata ◽  
Ehsan Jamali Hondori ◽  
Asuka Yamaguchi ◽  
Takanori Kagoshima ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Large Scale ◽  
Japan Trench ◽  
Helium Isotope ◽  
Normal Faults ◽  
Circulation System ◽  
Deep Penetration ◽  
Oceanic Plate ◽  
Seismic Reflection Data ◽  
Reflection Data

AbstractPlate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

High-frequency ground-motion variability for rough-fault ruptures  

2021 ◽  
Author(s):  
Jagdish Chandra Vyas ◽  
Martin Galis ◽  
Paul Martin Mai
Keyword(s):  
Ground Motion ◽  
Large Scale ◽  
Earthquake Ground Motion ◽  
Small Scale ◽  
Dynamic Rupture ◽  
Roughness Effects ◽  
Ground Shaking ◽  
Fault Surface ◽  
Fault Roughness ◽  
Ground Motion Variability

<p>Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited.  </p><p>In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites  to carry out statistical analysis.  </p><p>Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of  distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.</p>

Design of the viaducts for the Line 3 of the Riyadh Metro LRT in Saudi Arabia

2018 ◽  
Author(s):  
Paul-Emile Durand ◽  
Lucas Wise ◽  
Emmanuel Joy ◽  
Alain Rossetto
Keyword(s):  
Saudi Arabia ◽  
Large Scale ◽  
Parametric Design ◽  
Full Range ◽  
Design Approach ◽  
Construction Site ◽  
Box Girder ◽  
Construction Engineering ◽  
Long Span ◽  
Metro Project

<p>In June 2013, three consortia were awarded the three construction packages that constitute the whole Riyadh Metro Project in Saudi Arabia for a total of 6 lines and 180 kilometres.</p><p>International Bridge Technologies was in charge, as a subconsultant of Idom, of the complete structural scope of services for the 25.6 km of elevated viaduct that Riyadh Metro Package 2 comprises (Line 3, around 41.6 km, out of which 25.6 km are elevated). This scope consisted of the full range of services from conceptual tender design to final detailed design, including shop drawings production, construction engineering and construction site support.</p><p>The Line 3 elevated viaduct consists of a three-cells precast segmental box-girder with typical simply-supported spans of 37 m and special continuous spans of 50 m. Six long span structures with spans varying from 60 m to 95 m were required for the special crossings over existing interchanges. Typical and continuous spans are erected span-by-span with an overhead truss while long spans are erected in balanced cantilever with cranes on the ground or lifting frames on the deck.</p><p>The present paper is centred on the design of the elevated viaduct and presents the different structures with key features and how they were constructed to permit large scale standardisation and speed of construction. Some key design aspects are developed, in particular the design approach for the 3-cells box-girder as the most effective solution to satisfy the imposed aesthetic criteria. This paper also exposes the design approach adopted to produce a “design-for-demand” by relying as much as practically possible on a realistic modelling of the alignment and by limiting parametric design. This allowed for an optimisation of material quantities.</p>

Self-Undermining Rhetoric in the Past and Present

2015 ◽  
Author(s):  
Adam Seth Levine
Keyword(s):  
Collective Action ◽  
Policy Change ◽  
Large Scale ◽  
Political Change ◽  
Political Action ◽  
Full Range ◽  
Economic Insecurity ◽  
The Past ◽  
Broad Concept ◽  
The Face

This chapter considers the prospects for political change in the face of communicative barriers to collective action. It begins to address this question by identifying several of the most well-known historical and recent moments in which there was large-scale mobilization on some economic insecurity issues. This discussion, in concert with the empirical findings in this book, helps clarify the prospects for political action (and policy change) on these issues. The chapter then uses the findings from the book to identify three types of people that are most likely to become active. It also talks about the implications of having this (narrower) set of people active as opposed to the full range of people that find the issues to be important. It concludes by reiterating how self-undermining rhetoric is a broad concept that can apply in many different situations beyond those considered herein.

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