Lateral Gravity Research Articles

Insights on Lateral Gravity Wave Propagation in the Extratropical Stratosphere From 44 Years of ERA5 Data

AbstractThe study presents (a) a 44‐year wintertime climatology of resolved gravity wave (GW) fluxes and forcing in the extratropical stratosphere using ERA5, and (b) their composite evolution around gradual (final warming) and abrupt (sudden warming) transitions in the wintertime circulation, focusing on lateral fluxes. The transformed Eulerian mean equations are leveraged to provide a glimpse of the importance of GW lateral propagation (i.e., horizontal propagation) toward driving the wintertime stratospheric circulation by analyzing the relative contribution of the vertical versus meridional flux dissipation. The relative contribution from lateral propagation is found to be notable, especially in the Austral winter stratosphere where lateral (vertical) momentum flux convergence provides a peak climatological forcing of up to −0.5 (−3.5) m/s/day around 60°S at 40–45 km altitude. Prominent lateral propagation in the wintertime midlatitudes also contributes to the formation of belts of GW activity in both hemispheres.

Static strength design of local thickened plate joints between multi-cell concrete-filled steel tubular column and steel beam

A new-type local thickened plate joint (LTPJ) between multi-cell concrete-filled steel tubular columns (CSTC) and steel beams is adopted in residential building structures. However, no available strength design method for such beam-column joints is reported. This paper presents the mechanical behavior and static strength design of such joints. The local thickened plates are adopted to replace the normal thickness plates of the CSTCs within the LTPJ region. The rectangular section and L-shaped section of the multi-cell CSTC are involved in the joint study, respectively. Firstly, a finite element model (FEM) of the LTPJ between CSTCs and steel beams is established, which is then adopted to investigate the mechanical behaviour and static load-bearing capacity of the LTPJ. Codirectional and inverse bending moments are applied on the beams on two opposite sides of the LTPJ to simulate lateral loads (arise from wind or earthquake) and dead gravity loads, respectively. It is revealed that the LTPJ experiences shear failure when subjected to lateral loads, whereas it succumbs to bending failure when under dead gravity loads. The shear-bearing capacity of the LTPJ results from the three-part contribution of the steel tube web, the steel tube flange, and the core concrete. The bending-bearing capacity of the LTPJ is determined by the plate normal tension-bearing capacity of the steel tubes, which is predicted by adopting the theory of yielding line and numerical fitting. Finally, the load-bearing capacities of LTPJ under bidirectional bending moment are investigated numerically, and accordingly, some strength design recommendations are proposed in practical application. To conclude, these results provide a method for accurately predicting the load-bearing capacity of the LTPJ subjected to lateral loads and gravity loads, which holds the potential to expand and enhance the application of LTPJs and CSTCs in the design of high-rise residential buildings.

Emulating lateral gravity wave propagation in a global chemistry–climate model (EMAC v2.55.2) through horizontal flux redistribution

Abstract. The columnar approach of gravity wave (GW) parameterisations in weather and climate models has been identified as a potential reason for dynamical biases in middle-atmospheric dynamics. For example, GW momentum flux (GWMF) discrepancies between models and observations at 60∘ S arising through the lack of horizontal orographic GW propagation are suspected to cause deficiencies in representing the Antarctic polar vortex. However, due to the decomposition of the model domains onto different computing tasks for parallelisation, communication between horizontal grid boxes is computationally extremely expensive, making horizontal propagation of GWs unfeasible for global chemistry–climate simulations. To overcome this issue, we present a simplified solution to approximate horizontal GW propagation through redistribution of the GWMF at one single altitude by means of tailor-made redistribution maps. To generate the global redistribution maps averaged for each grid box, we use a parameterisation describing orography as a set of mountain ridges with specified location, orientation and height combined with a ray-tracing model describing lateral propagation of so-generated mountain waves. In the global chemistry–climate model (CCM) EMAC (ECHAM MESSy Atmospheric Chemistry), these maps then allow us to redistribute the GW momentum flux horizontally at one level, obtaining an affordable overhead of computing resources. The results of our simulations show GWMF and drag patterns that are horizontally more spread out than with the purely columnar approach; GWs are now also present above the ocean and regions without mountains. In this paper, we provide a detailed description of how the redistribution maps are computed and how the GWMF redistribution is implemented in the CCM. Moreover, an analysis shows why 15 km is the ideal altitude for the redistribution. First results with the redistributed orographic GWMF provide clear evidence that the redistributed GW drag in the Southern Hemisphere has the potential to modify and improve Antarctic polar vortex dynamics, thereby paving the way for enhanced credibility of CCM simulations and projections of polar stratospheric ozone.

Seismic Comparison of Diagrid and X-Bracing System in Highrise Building

Abstract: The diagrid (diagonal grid) structural design is one of the fascinating structural design ideas for sturdy tall constructions. Diagrid, a new design style for tall, intricate structures, has emerged due to its aesthetic appeal and structural effectiveness. Diagrid's façade structural system resists both lateral loads and gravity loads by utilizing a small grid of diagonal components. As it uses less structural steel than a conventional steel frame, making the structure more environmentally friendly. This study makes use of ETABS to assess tall structures built of Diagrid steel and tall structures using different bracing techniques. Being thin makes high-rise structures extremely vulnerable to lateral forces, thus they must be constructed to provide safety and comfort in accordancewith user needs. In order to combat the lateral stresses that are most common in high-rise structures, diagrid and X-bracing systems have been created. In this study, the seismic behaviors of diagrid and X-braced systems are compared.

Loess erosion change modeling during heavy rainfall

A typical gully sub-basin with a complex geomorphological form is used to do a model test of gravity erosion of loess by considering the sequence of slopes in a prototype gully creating a sequence of underlying surface forms in the upper reaches. The results show that the runoff from heavy rainfall is the main external force for the erosion of loess, and also is an important influencing factor to stimulate and intensify the development of gravity erosion. The soil structure and the height of the critical surface have a direct impact on the possibility of gravity erosion. Spatially, the upper section of the drainage channel mainly experiences undercutting and headcut erosion, the middle section mainly experiences lateral erosion and gravity erosion, and the lower section alternately experiences sedimentation or alluvial erosion. Rainfall splash erosion produces a large amount of sand to yield high concentration mud flows in the middle and lower sections of the channel. Because of the mud flows the flood flow is obviously larger than the runoff volume formed by rainfall in a small watershed. The flood formed by high-intensity rainfall brings a large amount of sediment into the downstream rivers along the channel, indicating that under the condition that high-intensity rainfall on the Loess Plateau, lots sediment will enter the Yellow River, and the erosion deformation occurs on all slopes. Further the steep slope drainage flow causes undercutting and lateral erosion, and the soil body moves down along the slope under the action of gravity. The gully in the middle section still experience sediment washing in both depth and width, and the downstream gully continues to experiences sedimentation due to the reduction of the gradient, reflecting the adaptive adjustment of water flow and the boundary. Headcut erosion occurred on almost all slopes during different periods of rainfall, while gravity erosion mostly occurred on steep slope sections during periods of high-intensity rainfall.

Numerical simulations of the spread of point‐source liquid spills in inclined and rolling rectangular packed beds

AbstractLiquid spreading in thin rectangular vertical/inclined and oscillating porous media was simulated using a two‐fluid dynamic model as a preliminary step in the design of fixed‐bed reactors dedicated to marine applications. The model assessed the influence of capillary pressure and mechanical dispersion forces arising from the spatial inhomogeneity of point‐source liquid injections in packed beds with different particle sizes, liquid and gas flow rates, liquid viscosity, static bed tilts, and rolling amplitudes and periods. In mildly static inclined beds, the lateral gravity force component and the capillary pressure force were the main factors affecting the liquid spreading. However, at considerable bed inclinations, the liquid phase accumulation in the lowermost regions of the packed bed tended to shrink the liquid spreading. Dynamic oscillatory evolutions of the liquid spills in the rolling bed enlarged the liquid spreading length as compared to the static vertical bed due to combined lateral liquid flow and increased liquid residence time.

Diagrid and Bracing System Comparative Structural Performance and Sustainability Concept

Abstract: One of the intriguing structural design concepts for robust tall structures is the diagrid (diagonal grid) structural design. Due to its attractiveness and structural efficiency, Diagrid, a new design trend for tall, complicated structures, has arisen. Using a compact grid of diagonal members, Diagrid's façade structural system resists both lateral loads and gravity loads. As opposed to a traditional steel frame, it employs less structural steel, resulting in a more environmentally friendly building. This research uses ETABS to examine the structural performance of tall structures made of Diagrid steel and tall buildings with various bracing systems. Therefore, the purpose of this study is to contrast the lateral displacement brought on by wind and earthquake load between high-rise structures (buildings) using the diagrid system and those using other bracing systems. The use of diagrid and other bracing systems in relation to the natural frequency of high-rise structures (buildings) is also investigated in this study. A 40-story building model has been taken for analysis in E-Tabs 2016, with a plan area of 1296m2 (36- meters x 36-meters) and 144 meters tall.

Resistivity imaging from magnetotelluric soundings of the Rio Preto Belt (NE Brazil): The role of lateral variations in the Precambrian basement on the evolution of phanerozoic basins

We present a resistivity model for the boundary of the Paleozoic Parnaíba Basin and the Cretaceous Sanfranciscana Basin (NE Brazil). The boundary underlies the Neoproterozoic Rio Preto belt, whose basement consists of reworked Archean and Paleoproterozoic rocks. In order to characterize the subsurface geoelectrically, 17 broadband magnetotelluric (MT) soundings were acquired and distributed along a ∼90 km profile across Rio Preto belt. The transfer functions were obtained with a robust code, thus obtaining reliable results for all four components of the impedance tensor. Some apparent resistivity and phase curves were shown to be heavily contaminated by local electromagnetic noise at low frequencies, and others showed minimal radio signals associated with the deadband frequency range. In this study, the MT data set was interpreted using 2D and 3D inversion procedures. Comparing the two MT models, the crustal-scale structure is well resolved in the 2D model, but the 3D model explains significantly better the measured data related to deep/shallow structures and proved to be more sensitive to conductive anomalies. The final resistivity image derived from the 3D inversion denotes a resistive basement with vertical conductive anomalies in the SE portion and a conductive domain in the NW portion. The homogeneous conductive block corresponds to the Archean domain of the Rio Preto belt, and the heterogeneous resistive block has the morphology and physical properties of the Paleoproterozoic block. Lateral geological correlation and gravity data support that the basement of the Parnaíba Basin in the study area is formed by the Archean block of the Rio Preto Belt. The boundary between the resistive blocks is a reverse fault that is also the tectonic front of a sub-horizontal detachment fault. In the Paleoproterozoic block, the conductors are associated with graphitic and volcano-sedimentary sequences, the dome and keel structures explain the geometry of the conductors. Additionally, graben-likes features were revealed in this block, interpreted as Cambrian basins filled by Cretaceous sediments of the Urucuia and Areado formations. These structures have a good correlation with those defined in the eastern edge of the Parnaíba Basin in previous studies. Towards the NW end of the section, the resistive blocks abruptly turn into a high conductivity domain (HCD) covered by a shallow conductive layer of Parnaíba Basin sandstones that modifies the electrical properties of the basement by interaction of basal fluids.

Effect of transverse circular and helical reinforcements on the performance of circular RC column under high explosive loading

Columns are primary load-carrying members of the framed structure which transfer external lateral loads and gravity load of the structure to the foundation. Columns under extreme loadings such as blast may become a local hazard, failure of which can lead to the disproportionate or progressive collapse of the building. Not only the subversive reasons but accidental explosions may also cause the failure of the column(s) or building, resulting in a huge loss of economy and human lives. Blast resistance of the columns in the building is of serious concern under explosive loadings. Following the validation of experimentally tested square RC column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT equivalent) at a scaled distance of 1.00 m/kg1/3 with 10 mm mesh size using ABAQUS/CAE software equipped with concrete damage plasticity model, equivalent circular columns to the experimentally tested one having seismic circular transverse reinforcement, and column with helical transverse reinforcement carrying the same axial load under the blast are considered. Additional transverse reinforcement of CFRP is also considered over confining regions. Additional wrappings of CFRP and mild steel sheets are also used to study their effect on the blast performance of the columns. Blast performance in terms of maximum displacement, stresses, and damage to the columns are compared and discussed. The present research provides insight into the blast performance of the circular RC columns and provisions to reduce the explosive-induced failure risk.

Comparison of spherical cap and rectangular harmonic analysis of airborne vector gravity data for high-resolution (1.5 km) local geopotential field models over Tanzania

SUMMARYThis study examines local geopotential field modelling over a mountainous region in Tanzania using vector airborne gravity data. We use the adjusted spherical cap and rectangular harmonic analyses. Both methods are based on expansion of gravitational potential into a series of orthogonal harmonic basis functions of local support in such a way that the expansion coefficients are determined by gravity observations. All three components of gravity vector are simultaneously inverted to derive the geopotential coefficients. In order to evaluate the accuracy of the local models, independent checkpoints are selected within the study region and around its boundary and the computed gravity vectors are compared with the independent gravity observations. The results show an excellent agreement with root mean square error (RMSE) of < 1.6 mGal over the study area. On the contrary, the RMSEs of global geopotential models against the checkpoints data are 7 mGal for the models up to the maximum degree of 2190 (a resolution of ∼9.1 km) and 5 mGal to 5399 (∼3.7 km). Our local models are significantly more accurate than the state-of-the-art global models and fully exploit the airborne vector data with the measurement error of ∼1 mGal. We also present the regional models constrained only by radial (vertical) or by lateral (horizontal) gravity observations. Those models are considerably less accurate than the one from 3-D gravity data inversion. Lastly, the regional models are validated against topography data. It is found that the gravity–topography correlation is 0.8–0.9 at 100 km, 0.5 at 20 km and higher than the correlations of the global models at all frequencies. The gravity–topography admittances estimated from our regional models indicate ∼130 mGal km−1 and imply the effective density of 2500 kg m−3 for topographical mass.

Layered crustal azimuthal anisotropy beneath the northeastern Tibetan Plateau revealed by Rayleigh-wave Eikonal tomography

The uplift of the Tibetan Plateau in the Cenozoic has greatly affected the tectonics in Asia. But the evolution of the plateau is still unclear. The northeastern Tibetan Plateau is under ongoing expansion and is therefore essential for understanding the tectonic evolution of the plateau. Using data from 675 stations deployed by the ChinArray project, we obtained an anisotropic shear-wave velocity model by Rayleigh-wave phase-velocity Eikonal tomography and further investigated layered anisotropy and deformation patterns in the northeastern Tibetan Plateau. In the upper crust (<20 km depth), the fast directions are parallel with major strike-slip faults. In the lower crust, the fast directions are mostly margin-parallel along the plateau margin (at depths of ∼20 km to Moho), but they are perpendicular to the plateau margin while parallel to the topographic gradient under the high plateau (at depths of ∼40 km to Moho). Our result indicates that there is lower crustal flow under the high plateau due to the differential lateral gravity potential. However, the deep crustal flow is blocked by the surrounding blocks, which results in pure shear along the plateau margin in the northeastern Tibetan Plateau.

Design and optimization of integrated flexure mounts for unloading lateral gravity of a lightweight mirror for space application.

This paper presents an integrated flexure mount (IFM) to unload the lateral gravity of a lightweight mirror. The significance of the position relationship between the plane of mirror centroid and the center of flexure pivot is analyzed using the coupling kinematic stiffness model of the flexure mounts derived in this paper. Based on the analysis, an IFM with S-type flexure hinges was designed, and the structure and assembly are described. Then, the optimal position and size parameters of an S-type flexure hinge were obtained by optimization. The optimization results attained by finite element analysis (FEA) indicate that the optimization objectives and constraints were satisfied. Moreover, the degradation of the mirror's optical performance caused by lateral gravity was minimized, and the effects of temperature variation and assembly tolerance were reduced. The IFMs were fabricated based on the optimization results and assembled with a mirror prototype for a pointing precision test and sine-frequency sweep test. A FEA and test results for the IFMs confirm the validity and feasibility of the flexure mounts model and structure design, and we believe the IFM meets the requirements of a lightweight mirror for space application.

Analyzing different configurations of variable angle diagrid structures

Abstract Diagrid structures are popular among engineers and architects. The reason for this is its structural efficiency due to carrying both lateral loads and gravity loads and aesthetic attributes. Recent research has shown that using variable angle diagrids for a structure can be more efficient than using diagrid structures with constant angle of inclination. This paper provides an analysis of different configurations of the variable angle diagrid structures. For this purpose, the parameters of variable angle diagrid structures such as angle of inclination of diagrids and the ratio of heights for which angle of inclination of diagrids are varied to study its effect on the structure. Different patterns of variable angle diagrid structures are generated for a 60 storied building which are modelled and analysed in ETABS under gravity and wind loads. The optimum configuration is selected from these diagrid configurations based on the structural weights of diagrids and performances of the building.

Post-earthquake fire behavior and performance-based fire design of steel moment frame buildings

This paper presents an assessment of steel buildings subjected to post-earthquake fire, illustrated through the implementation of a ten-story case study building, which was designed in accordance with U.S. design codes. The building is located in a high seismic region (Los Angeles, CA), and designed for the associated seismic hazard levels using perimeter special moment frames (SMFs) to resist lateral (wind and seismic) loading and gravity interior frames with composite floor systems to resist gravity (dead and live) loading. The entire 3D building structure was idealized and analyzed using finite element models capable of modeling inelastic deformations, instability failures, and connection damage due to earthquakes and fire. The building models were subjected to eleven earthquakes followed by three different fire scenarios to simulate the effects of post-earthquake fires. The results from post-earthquake fire analyses were used to assess the impact of earthquake-induced damage on structural behavior and stability during fire. Assessments indicate that, for the type and design of structure considered in this research, earthquake-induced damage is generally limited to the perimeter moment frames and has limited influence on post-earthquake fire performance, which is governed by the strength and stability of gravity columns and floor systems. Analytical parametric studies were conducted to further assess and develop performance-based design guidelines for improving structural behavior and stability during post-earthquake fires. These studies indicate that partial or full collapse of the building structure can be prevented by sufficiently increasing the structural design (size) or fire protection (fireproofing thickness) of the critical gravity columns.

A Case Study on the Selection of Optimum Loop Units for the Deployable Arch Structures Exposed to Lateral and Non-uniform Gravity Loads

Radially deployable arches may be created by using various types of units. However, for any deployable structure to be constructed in real life, it should satisfy the structural regulations and codes. Despite various advantages from architectural perspective, deployable structures are weak to satisfy the operational code limits when compared to trusses with similar height and span. Therefore, weight minimization is very important to reduce the dead loads of the structure which facilitates the code-conformance of the structure. The optimization of the deployable structures requires an initial selection of the loop types to define the structure parametrically. An initial selection strategy depending on the loads on the structure is important to increase the efficiency of optimization process. Under uniform gravity loads, optimum arrangement for each unit type converges to a similar point. However, in the real world, the loads on the arches are not always uniform and the structure is exposed to non-uniform loadings such as point loads or lateral loads. This work focuses on the performance of various arches with different unit types under lateral and non-uniform vertical loads. Different lateral load and non-uniform gravity loading scenarios are created. For each scenario, the arches with different units are analyzed. In all cases, clear span and height are kept as same. The performance of an arch with a specific unit type for a given load is measured with a score that includes the deformations and the weight of the structure. All the members are assumed to be circular hollow sections with variable diameter and thickness to have a meaningful weight comparison between structures. This work intends to define an initial selection guide for deployable arches under typical non-uniform and lateral loading conditions.

Reduction in Shear Lag Effects in Tall Buildings Using Exterior Bracing and Diagrid Systems (Recent Developments-review paper)

The structural and architectural aspects of the exterior bracing and diagrid systems - two systems which generally reduce building materials, enhance structural performance, and decrease overall construction cost achieve sustainability. When a structure is completed it is expected to look elegant, appealing and, above all it must be structurally correct. These structural systems, diagrids and exterior bracings can visually communicate the inherent structural logic of a building while giving artistic effect. This creates the structural elements that are aesthetically pleasing and geometrically coherent, while also respecting the laws of mechanics. The diagrid (diagonal grid) structural system has now become increasingly popular. A diagrid system consists of series of triangles and horizontal rings of beams which provide the structure support against gravity and lateral forces, while also making a building stiffer and often lighter than a traditional high-rise. Diagrids are usually composed of steel, because of its high strength and ability to resist both tensile and compressive forces. The diagrid can suffer from problems of implementation due to its complicated steel joints, but recent advances in joint detailing and prefabrication are helping to address this issue. Due to their triangular configuration, diagrids can efficiently carry the shear and moment caused by lateral loads and gravity. They are effective in minimizing shear deformation, providing maximum resistance against torsion. In this paper, shear lag effect is being studied based on various works reported and is correlated with stiffness of the building. The study is also done for the different patterns of bracing systems the blend of structural performance and aesthetics, examined to facilitate a better understanding of the aesthetic developments in skyscrapers around the world. For this purpose, different geometric patterns of bracing system are considered. For a relative study for shear lag effect, cross-sectional dimensions of beam and columns, their alignments (column) and the material properties are assumed to be same throughout the height of the building. It is found that bracing system considerably reduces the shear lag effect and hence increases the building stiffness to withstand lateral loads.

Lightweight Design of Multi-Objective Topology for a Large-Aperture Space Mirror

For a large-aperture space telescope, one of the key techniques is the method for designing the lightweight primary mirror assembly (PMA). In order to minimize the mirror surface error under axial gravity, lateral gravity, and polishing pressure at the same time, a method for topology optimization with multi-objective function combined with parametric optimization is introduced in this paper. The weighted compliance minimum is selected as the objective function to maximum the mirror structural stiffness. Then sensitivity analysis method and size optimization are used to determine the mirror structure parameters. Compared with two types of commonly used lightweight configurations, the new configuration design shows obvious superiority. In addition, the surface figure root mean square (RMS) of the mirror mounted by given bipod flexure (BF) under 1 g lateral gravity is minimized only with a value of 3.58 nm, which proves the effectiveness of the design method proposed in this paper.

Subsurface imaging of the Harrat Lunayyir 2007–2009 earthquake swarm zone, western Saudi Arabia, using potential field methods

The Harrat Lunayyir (HL) 2007–2009 earthquake swarm has attracted much scientific interest mainly due to its occurrence within the Large Igneous Province (LIP) of Saudi Arabia. Qualitative interpretation of aeromagnetic anomalies is suggestive of linear dike-like anomalies, striking NW-SE, across the earthquake swarm zone (ESZ). Residual Bouguer anomaly data for HL range between −4.3 and 1.5 mgal and show a 20 km-wide gravity low flanked by lateral gravity highs. The axial-zone of low gravity corresponds to the ESZ cluster. Employing a three-dimensional (3D) inversion of the residual gravity field with a one-dimensional (1D) P-wave velocity model as a proxy for background density variations with depth, we imaged a mid-to-upper crustal low density zone (>10 km depth). We interpret this zone as the source area of ascending magma that intruded into the upper crust underlying the HL during the 2009 seismic crisis. The inversion also highlights lower than average density rocks beneath the western parts of the HL whereas its eastern part is composed of rocks of higher density. The 3D magnetic inversions lead us to infer magmatic intrusion of lower magnetic susceptibility at this locality extending vertically from 1.57 km altitude (above sea level) to its bottom edge at 10.8 km depth (below sea level). Based on these results, the 2007–2009 ESZ is likely associated with rift-related extension associated with the Red Sea spreading, where a trans-crustal magmatic plumbing system extends to depths of about 10 km beneath the centre of HL.

Using salt tectonic structures as proxies to reveal post-rift crustal tectonics: The example of the Eastern Sardinian margin (Western Tyrrhenian Sea)

Abstract The METYSS project (Messinian Event in the Tyrrhenian from Seismic Study) is based on high-resolution seismic data acquired along the Eastern Sardinian margin, Western Tyrrhenian Sea. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigated the thinning processes of the continental crust and the timing of crustal vertical movements across this backarc domain. Our first results shown that rifting ended before the MSC, but that crustal activity persisted long after the end of the rifting. This has been particularly observed on the proximal margin, the East-Sardinia Basin, where the Mobile Unit (MU, mobile Messinian salt) is thin or absent. In this study, we examined the distal margin, the Cornaglia Terrace, where the MU accumulated during the MSC and acted as a decollement, thus potentially decoupling the basement from the sedimentary cover. Our observations provide evidence for lateral flow and gravity gliding of the salt and its brittle sedimentary overburden along local basement slopes generated by the post-MSC tilting of some basement blocks formerly generated during the rifting. We also investigated an intriguing wedge-shaped body of MU located in a narrow N-S half graben bounded to the west by a major, east-dipping, crustal normal fault. Classically, one could think that this salt wedge is related to the syn-tectonics deposition of the MU, but we propose an original scenario, in which the post-rift vertical motion of the major fault has been cushioned by lateral flow of an initially tabular salt layer, leaving the supra-salt series apparently unaffected by the crustal motions of the basement. We tested this scenario by comparing natural data and physical (analogue) modelling data. Our results reveal that salt tectonics provides a powerful tool to understand the deep crustal tectonics of the margin and to constrain the timing of vertical motions in the Western Tyrrhenian Basin, results that can be applied to rifted salt-bearing margins worldwide.

Predicting the vortex shedding frequency at the interface of the lateral cavities

The vortex shedding frequency in the mixing layer between a cavity and a main stream has been examined experimentally in absence of large oscillation of the free surface inside the cavity, called seiching. It was observed that the vortex shedding frequency follows a monotonically increasing trends with possible jumps from one to another with increasing Froude number of the main stream. These trends are obtained by solving a model based on the Rossiter approach. This model considers that the vortices shed in the mixing layer create some water depth variation at the impingement corner of the cavity. This water depth variation in turn generate pressure waves that propagates upstream and influence the vortex shedding process. Finally the measured vortex shedding frequencies correspond quite accurately to the frequencies predicted by the model. This highlights the existence of a resonant phenomena between vortices in the mixing layer of a lateral cavity and gravity waves even without any seiching phenomena.