Ramp Geometry Research Articles

Constraining the strength of megathrusts from fault geometries and application to the Alpine collision zone

Using Coulomb wedge solutions, we show that the effective strength of megathrusts (μb′) can be determined from the geometry of out-of-sequence thrusts cutting through an accretionary or orogenic wedge. The method is first tested on central Chilean margin for which it yields a frictional strength of μb′=0.053 (+0.043/−0.024). The inferred value agrees well with previous strength estimates and with the tectonic response of the central Chilean wedge to 2010 Mw 8.8 Maule earthquake. We then use the approach to constrain the strength of the collision megathrust of the central European Alps ∼30–20 million years ago. We find that the collision megathrust had a strength of μb′=0.065 (+0.035/−0.026), which is similarly low than the strength of subduction megathrusts. The result is integrated into a static force balance model to examine potential implications of a weak megathrust for the Alpine orogeny. The model results suggest that the Alpine megathrust supported a mean maximum elevation of ∼2,000 m and that growth of the wedge up to this elevation supported a switch from contractional to extensional tectonics in the interior of the Alps around 20 Ma. Finally, using the example of the Himalayas, we show how the strength of megathrusts may be also derived from the geometry of crustal ramps, which provides a valuable alternative if details on out-of-sequence thrusts are missing.

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.

Mechanical models favor a ramp geometry for the Ventura‐pitas point fault, California

AbstractRecent investigations have provided new and significantly revised constraints on the subsurface structure of the Ventura‐Pitas Point fault system in southern California; however, few data directly constrain fault surfaces below ~6 km depth. Here, we use geometrically complex three‐dimensional mechanical models driven by current geodetic strain rates to test two proposed subsurface models of the fault system. We find that the model that incorporates a ramp geometry for the Ventura‐Pitas Point fault better reproduces both the regional long term geologic slip rate data and interseismic GPS observations of uplift in the Santa Ynez Mountains. The model‐calculated average reverse slip rate for the Ventura‐Pitas Point fault is 3.5 ± 0.3 mm/yr, although slip rates are spatially variable on the fault surface with > 8 mm/yr predicted on portions of the lower ramp section at depth.

Multidisciplinary inferences on a newly recognized active east‐dipping extensional system in Central Italy

AbstractWe use a multidisciplinary approach to gather preliminary evidence for a Quaternary east‐dipping extensional detachment in Central Italy. This structure crops out in the Sabini‐Eastern Simbruini (SES) and would be hidden at mid‐crustal depths beneath the L'Aquila 2009 (Mw6.3) epicentral area. TheSESgeometry is reconstructed through geological mapping, structural analysis and seismic line interpretation. The geometry of the mid‐crustal segment, referred to as the Ocre Segment (OS), is interpreted through seismological analyses of the largest aftershock (Mw5.4) of the L'Aquila 2009 sequence. The kinematic compatibility between theSESand theOSunder a commonSW–NEtensional field is tested through stress inversion of both geological and seismological data. The reliability ofOSactivation is tested through slip tendency analysis. Like other Italian cases, theSESand theOSare preliminarily interpreted as expressions at different depths of the same unknown east‐dipping extensional detachment, characterized by a ramp–flat–ramp geometry.

Alpine tectonic wedging and crustal delamination in the Cantabrian Mountains (NW Spain)

Abstract. The Cantabrian Mountains have been interpreted as a Paleozoic basement block uplifted during an Alpine deformation event that led to the partial closure of the Bay of Biscay and the building of the Pyrenean range in the Cenozoic. A detailed interpretation of deep seismic reflection profile ESCIN-2 and the two-dimensional seismic modelling of the data allowed us to construct a N–S geological cross section along the southern border of the Cantabrian Mountains and the transition to the Duero Cenozoic foreland basin, highlighting the Alpine structure. The proposed geological cross section has been constrained by all geophysical data available, including a 2-D gravity model constructed for this study as well as refraction and magnetotelluric models from previous studies. A set of south-vergent thrusts dipping 30 to 36° to the north, cut the upper crust with a ramp geometry and sole in the boundary with the middle crust. These thrusts are responsible for the uplift and the main Alpine deformation in the Cantabrian Mountains. A conspicuous reflective Moho shows that the crust thickens northwards from the Duero basin, where subhorizontal Moho is 32 km deep, to 47 km in the northernmost end of ESCIN-2, where Moho dips to the north beneath the Cantabrian Mountains. Further north, out of the profile, Moho reaches a maximum depth of 55 km, according to wide-angle/refraction data. ESCIN-2 indicates the presence of a tectonic wedge of the crust of the Cantabrian margin beneath the Cantabrian Mountains, which is indented from north to south into the delaminated Iberian crust, forcing its northward subduction.

Pressure sensitive paint measurements at high Mach numbers

Depending on the case study examined, different PSPs may be used, each applied using a different method onto the model. For polymer PSP the paint is sprayed on. In contrast, the model may first be anodised or covered with a thin-layer chromatography plate and then dipped in PSP. The objective of the present study is to analyse the characteristics of different PSP substrates at high Mach numbers which use two well-known PSP molecules: (i) tris-Bathophenanthroline Ruthenium (II) Perchlorate and (ii) Platinum-tetrakis (pentafluorophenyl) Porphyrin. Using a double ramp geometry under a Mach 5 hypersonic flow the feasibility of applying each of the aforementioned PSP methods is investigated and compared to discrete pressure measurements. The flow over a 3D bump under a Mach 1.3 flow is also studied to give a broader Mach number range. In the hypersonic tunnel, all PSP techniques and formulations were able to capture the complex flowfield with the results quantitatively agreeing with the discrete measurements. For the transonic bumps however, it was found that the polymer based Platinum PSP could map the flowfield more accurately.

Constructal Design de um dispositivo de galgamento onshore em escala real para uma profundidade fixa

O estudo a respeito das tecnologias e princípios de funcionamento de dispositivos de conversão de energia das ondas em energia elétrica (WEC) tem crescido sensivelmente. Entre os WECs estudados está o dispositivo de galgamento. O seu princípio físico de funcionamento consiste em uma rampa que guia a água das ondas incidentes para um reservatório localizado acima do nível médio do mar. A água acumulada no reservatório escoa através de uma turbina de baixa queda gerando energia elétrica. No presente trabalho é realizado um estudo numérico relacionado ao efeito da geometria da rampa sobre o desempenho de um dispositivo de galgamento <em>onshore</em> em escala real, empregando <em>Constructal Design</em>. O principal propósito aqui é avaliar a razão entre altura e comprimento da rampa (<em>H</em><sub>1</sub>/<em>L</em><sub>1</sub>) que maximiza a quantidade de água que entra no reservatório do dispositivo para uma distância entre o fundo do dispositivo e o fundo do tanque de <em>S</em> = 6.0 m. Nas presentes simulações, as equações de conservação de massa, quantidade de movimento e uma equação para o transporte da fração volumétrica são resolvidas com o método dos volumes finitos (MVF). Para abordar a mistura água e ar, o modelo multifásico <em>Volume of Fluid</em> (VOF) é empregado. Os resultados mostraram que as melhores geometrias são obtidas para as menores razões de <em>H</em><sub>1</sub>/<em>L</em><sub>1</sub> para a profundidade analisada, contrariamente ao que foi observado em estudos preliminares da literatura para um dispositivo no meio do canal em escala de laboratório que simulava um dispositivo de galgamento do tipo <em>offshore</em>.

Variations in petrophysical properties along a mixed siliciclastic carbonate ramp (Upper Jurassic, Ricla, NE Spain)

A multi-scale petrophysical study was performed on an Upper Jurassic siliciclastic – carbonate ramp system near the village of Ricla (Spain). A combination of textural (field observations, thin section and grain-size analysis), chemical – mineralogical (thermo gravimetric analysis) and physical (porosity, gamma ray and velocity measurements) properties was used to capture the heterogeneity of this mixed sedimentary system. Subsequently, synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp-structures. The translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic. Although upscaling problems are a recurring issue, the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties.Acoustic properties are generally controlled by the amount and type of pore spaces. Due to the low porosities (ϕ < 7.2%) of this mixed ramp system the influence on the acoustic properties is limited; therefore other controlling parameters come into play. One of the primary controlling factors is the mineral composition, thus the presence of clay and the ratio between siliciclastic and carbonate components. A dominant presence of carbonate relates to relative high P- and lower S-wave velocities, a high percentage of quartz relates to relative lower P- and higher S-wave velocities, the presence of clay reduces the overall velocities even more. Carbonate infill of intergranular space (micrite or cement) slightly influences the acoustic properties. In general, the infill of microporous micrite shows lower velocities compared to the cemented samples. Finally microcracks may significantly reduce the velocity, although these cannot be quantified, their presence can be estimated using elastic property models.The ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity. Textural, sedimentological and stratigraphic transitions in the outcrop are related to the defined facies, each has its own unique mineralogical signature. Amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions.

Constructal design of an onshore overtopping device in real scale for two different depths

In this work, a 2D numerical study was performed on the effect of the ramp geometry on the performance of an onshore overtopping device in real scale employing constructal design. More precisely, it evaluates the effect of ratio between height and length of the ramp (H 1/L 1) over the mass of water (m) entering the reservoir for two different depths (S = 5.0 m and 6.0 m). For all simulations, the ramp device area is maintained constant. A computational model based on the finite volume method and volume of fluid to tackle with the mixture of water/air was employed. The once maximized mass entering reservoir (m m) increases with S, as expected. However, the best geometries changed with the device depth (S), showing that there is no universal shape that maximizes the performance of the wave energy converter device. The submergence also presented a strong influence over the transient behavior of the mass flow rate of water entering the reservoir of the overtopping device.

Magnetic susceptibility and facies relationship in Bajocian–Bathonian carbonates from the Azé caves, southeastern Paris Basin, France

Abstract This study focuses on three Bajocian and Bathonian carbonate sections from the southeastern part of the Paris Basin (Mâconnais area, in the east of France). The main goals of the study are to propose a palaeoenvironmental model, to get insight into vertical and lateral facies evolution, to improve correlations and to better understand the origin of the magnetic susceptibility (MS) signal in these deposits. The sedimentological setting corresponds to a ramp, with two types of geometries: (1) a homoclinal carbonate ramp with oolitic shoals; and (2) a multiple-slopes carbonate ramp with reef complexes. The MS signal appears to be influenced by facies and ramp geometry. The evolution of MS seems to be mainly related to changes in carbonate productivity and water agitation: oolitic facies and reef complexes, with high carbonate production show the lowest signal, while storm deposits are characterized by higher values. In addition, the MS signal from proximal tempestites have higher values than distal ones. MS appears to be a useful complementary proxy for palaeoenvironmental interpretations, correlations and sequential stratigraphy. The facies evolution, supported by MS curves, shows at least nine successive depositional sequences, which were inserted into the regional sequential canvas.

Predicting Crashes on Expressway Ramps with Real-Time Traffic and Weather Data

Limited research has been conducted on real-time crash analysis of expressway ramps, although there have been many studies in recent years on estimating real-time crash prediction models for main lines. This study presents Bayesian logistic regression models for single-vehicle (SV) and multivehicle (MV) crashes on expressway ramps by using real-time microwave vehicle detection system data, real-time weather data, and ramp geometric information. The results find that the logarithm of the vehicle count, average speed in a 5-min interval, and visibility are significant factors for the occurrence of SV and MV crashes. The Bayesian logistic regression models show that curved ramps and wet road surfaces would increase the possibility of an SV crash, and off-ramps would result in high risk of MV crashes. The high standard deviation of speed in a 5-min interval would significantly increase MV crash likelihood. Random Forests software was applied in variable importance analysis, and the results revealed that the most important factors influencing crashes on ramps were traffic variables, the second most important factors are weather variables, and the least important but still significant factor was the ramp geometry.

Shock boundary layer interactions in a low aspect ratio duct

Experimental data acquired using high resolution two-component particle image velocimetry (PIV) are presented for shock boundary layer interactions (SBLIs) generated by a compression–expansion ramp geometry. The incident oblique shock wave is generated by a sub-boundary layer height ramp inclined 20° to the M∞=2.05 inflow. Results are presented for two different ramp sizes (hramp/δ0=0.56 and hramp/δ0=0.93), and compared to a previously documented hramp/δ0=0.20 case. For each case, mean velocitiy and turbulent statistics for both the SBLI at the foot of the compression ramp and the incident/reflected SBLI on the opposite wall are analyzed. Data are acquired in several streamwise-vertical planes across the span of the low aspect ratio duct in order to document spanwise non-uniformities and confinement effects, with the specific goal of producing a high quality experimental database for CFD validation. The angles of the incident and reflected shock waves become steeper as the side wall is approached, due to the lower velocities within the side wall boundary layer. Mean flow reversal is observed near the spanwise centerline of the duct, but only instantaneous flow reversal is seen closer to the side walls. These spanwise non-uniformities are more prominent for the stronger interactions caused by the larger ramp geometry. For this case there is no nominally two-dimensional region of the flow, and a Mach stem occurs in the core of the flow, causing a significant subsonic wake. The shock excursion length scale relative to the incoming boundary layer thickness, Lex/δ0, is measured for all of the shock features and found to be significantly lower than values reported in the literature for similar flows. Furthermore, Lex/δ0 for the reflected shock does not depend on the strength of the incident shock or the size of the separated zone.

3D structure and evolution of folds during normal fault dip linkage

Understanding the 3D geometry and evolution of extension-related folds is important because they may document the geometry and evolution of the associated faults, influence sediment routing and accommodation development, and may represent targets for hydrocarbon exploration or CO 2 storage. Previous work on extension-related folds has largely been restricted to a 2D plane of observation; in this study we use 3D seismic reflection data from the Gulf of Suez, Egypt to determine the 3D geometry and evolution of fault-parallel folds during dip linkage of a vertically segmented extensional fault array that is locally decoupled across a salt-bearing interval. The 3D geometry of individual faults in the array and adjacent hanging-wall folds varies along strike; rollover structures occur above listric faults, whereas fault-bend folds occur above faults that have a ramp–flat–ramp geometry. Quantitative analysis of fault–fold attributes (e.g. fold amplitude) and the growth history of the fault array indicate that fault shape is controlled by the style of dip linkage, which in turn is controlled by the lateral separation of sub- and supra-salt segments prior to linkage. Small lateral separation yields a relatively subtle change in the overall convexity of the listric fault, whereas larger lateral separation results in a ramp–flat–ramp fault geometry, with the layer-parallel detachment lying within the salt. This study provides a link between fault spacing, style of dip linkage, final fault shape and, ultimately, the style of hanging-wall folding in mechanically layered stratigraphy. Our study indicates that 3D seismic reflection data have the ability to provide us with new 3D insights into the variability of, and controls on, the geometry and evolution of fault-related folds.

Numerical Study of the Effect of the Relative Depth on the Overtopping Wave Energy Converters According to Constructal Design

The conversion of wave energy in electrical one has been increasingly studied. One example of wave energy converter (WEC) is the overtopping device. Its main operational principle consists of a ramp which guides the incoming waves into a reservoir raised slightly above the sea level. The accumulated water in the reservoir flows through a low head turbine generating electricity. In this sense, it is performed a numerical study concerned with the geometric optimization of an overtopping WEC for various relative depths: d/λ = 0.3, 0.5 and 0.62, by means of Constructal Design. The main purpose is to evaluate the effect of the relative depth on the design of the ramp geometry (ratio between the ramp height and its length: H1/L1) as well as, investigate the shape which leads to the highest amount of water that insides the reservoir. In the present simulations, the conservation equations of mass, momentum and one equation for the transport of volumetric fraction are solved with the finite volume method (FVM). To tackle with water-air mixture, the multiphase model Volume of Fluid (VOF) is used. Results showed that the optimal shape, (H1/L1)o, has a strong dependence of the relative depth, i.e., there is no universal shape that leads to the best performance of an overtopping device for several wave conditions.

Effect of height of microvortex generators on swept shock wave boundary layer interactions

A numerical study to evaluate the critical height of microvortex generators in controlling swept shock wave boundary layer interactions is carried out. The planar shock wave is generated by placing a 20° sharp fin in a supersonic flow at Mach 4. The ramp and thick vane microvortex generator geometries were considered. The device heights were varied from 30 to 90 % of the incoming boundary layer thickness. The efficacy of the devices was observed to increase with increasing device height up to a height of 70 % of the incoming boundary layer thickness beyond which no further improvement was achieved.

Geometry and kinematics of the Montelanico-Carpineto Backthrust (Lepini Mts., Latium) in the hangingwall of the early Messinian thrust front of the central Apennines: implications for the Apennine chain building

The paper updates knowledge on the Montelanico-Carpineto Backthrust, which is confined in the Lepini Mts. thrust sheet, at the hangingwall of the Neogene Latina Valley Thrust Front.The local stratigraphic setting consists of a pre-orogenic succession of Mesozoic carbonates from the Latium-Abruzzi platform Auct. The carbonates are paraconformably overlain by Miocene ramp limestones, which evolve upwards into planktonic marls. The Sub-Ligurian unit thrusted over this dominantly carbonate succession.In the Latina Valley, siliciclastic turbidites (Frosinone Formation Auct.), which evolved from the above-mentioned Miocene units, constitute the upper Tortonian foredeep deposits, now preserved in the footwall of the Lepini Mts. thrust sheet. In the Segni-Montelanico area, conglomerates, unconformably overlying the carbonatebedrock and coeval with the Frosinone Formation, are interpreted as late Tortonian thrust-top deposits (Gavignano and Gorga unit). The Lepini Mts. ridge has two series of distinctive tectonic features: the first is related to the Neogene shortening events due to the Apennine chain building; the other results from Plio-Quaternary extensional events associated with the collapse of the Tyrrhenian margin.The Montelanico-Carpineto Backthrust, as evidenced by the structural survey, is a compressive fault plane dipping 45°-50° towards NE with a SW-verging dip-slip kinematics. The fault has an offset of about 700 m, ramp geometries and a cut-off of about 20°. The Montelanico-Carpineto Backthrust and the Latina Valley Thrust Front define a pop-up structure. The presumable age of the Montelanico-Carpineto Backthrust is the early Messinian, because the lateTortonian Gavignano and Gorga unit is involved in its brittle shear zone. This implies that the formation of the Montelanico-Carpineto Backthrust and of the related pop-up structure is coeval with the early Messinian thrusting of the Lepini Mts. thrust sheet upon the geodynamic propagation of the central Apennine chain-foredeep-foreland system.

Josephson φ-junctions based on structures with complex normal/ferromagnet bilayer

We demonstrate that Josephson devices with a nontrivial phase difference 0 < φg < π in the ground state can be realized in structures composed of longitudinally oriented normal metal (N) and ferromagnet (F) films in the weak link region. Oscillatory coupling across the F-layer makes the first harmonic in the current–phase relation relatively small, while coupling across the N-layer provides a negative sign of the second harmonic. To derive quantitative criteria for a φ-junction, we have solved the two-dimensional boundary-value problem in the frame of Usadel equations for overlap and ramp geometries of S–NF–S structures. Our numerical estimates show that φ-junctions can be fabricated using up-to-date technology.

Upper‐crustal extension during oblique collision: the Temsamane extensional detachment (eastern Rif, Morocco)

Terra Nova, 24, 505–512, 2012AbstractThe subducted North Maghrebian passive margin was exhumed in the Tortonian (11–7 Ma) by an upper‐crustal brittle‐ductile extensional detachment and brittle low‐angle normal faults in a continental subduction transform setting. The Temsamane detachment in the eastern Rif is defined by a ductile shear zone approximately 100‐m thick with a low‐angle ramp geometry that cuts down into the Temsamane fold‐nappe stack. The shear zone shows south‐westward kinematics and separates lower‐greenschist (≈400 °C) metapelites of the Temsamane units below from the anchizone and diagenetic rocks (&lt;300–200 °C) of the Ketama‐Aknoul units above. To the east, the detachment becomes brittle, branching into a listric‐fan that cuts through 10–6 Ma sediments and volcanoclastics in the Tres Forcas cape. Both the North Maghrebian and the South Iberian subducted passive margins were exhumed in the Betic and Rif branches of the Gibraltar arc by SW‐directed brittle‐ductile detachments during the late Miocene in an oblique collisional setting.

Sea‐level and ocean‐current control on carbonate‐platform growth, Maldives, Indian Ocean

AbstractMultichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region.

The Triassic platform of the Gador-Turon unit (Alpujarride complex, Betic Cordillera, southeast Spain): climate versus tectonic factors controlling platform architecture

A litho-biostratigraphic analysis has been carried out in the Gador-Turon unit of the Sierra de Gador (Alpujarride complex, Betic Cordillera, SE Spain). The Triassic succession of this unit is composed of a lower meta-detrital formation overlain by an upper meta-carbonate formation divided in six members. In the latter, a Ladinian–Carnian-rich fossil association has been found (foraminifers, algae, bivalves, microproblematica, trace fossils). Facies analysis has enabled the recognition of 22 facies of platform origin. This succession accumulated as a subsiding margin-type carbonate platform with homoclinal ramp geometry (Anisian?–Ladinian) evolving into a fault-block-type platform with a steeper-margined geometry (Ladinian–Carnian). Slope deposits of this latter platform show a prism-like geometry with progradational patterns and include syn-sedimentary structures associated with normal faults capped by younger beds. The results of the present research indicate that the architecture of the platform studied has been controlled mainly by climate and oceanic factors during the development of the ramp, and by syn-sedimentary extensional tectonics during the development of the steeper-margined platform. The Ladinian–Carnian tectonic activity was probably also responsible for the siliciclastic input and the shift to a mixed terrigenous-carbonate platform.