Horizontal Amplitude Research Articles

Local magnitude determination for Turkey from two independent seismic networks and a consistent M4 + catalogue

SUMMARY Turkish seismicity is routinely recorded by two broad-band seismic networks: the Turkish National Seismic Network (AFAD ‘TU’ network) and the Bogazici University Kandilli Observatory And Earthquake Research Institute (KOERI ‘KO’ network). Each of them has over 200 seismic stations distributed across the country. We obtain a new uniform and consistent local magnitude (Ml) scale for Turkey using data from both networks, as well as the M4 + catalogue with Ml values that results from applying said scale to the events that occurred between 2007 and 2016 within the country. We measure the half peak-to-peak amplitude of the vertical component seismograms and estimate the attenuation parameters through an iterative procedure that fits the logarithm of the amplitude as a function of the hypocentral distance, the local magnitude, the station corrections and a constant accounting for possible systematic differences between amplitudes measured on horizontal seismographs and those measured on vertical seismographs. We additionally scale Ml to the moment magnitude measured by an independent source, obtaining a magnitude relationship accounting for attenuation adjustments, as well as differences between maximum horizontal and vertical amplitudes. The estimated Ml formula shows that station corrections from both networks regionally agree, and that non-zero corrections are centred on zero, within −0.48 and 0.46 magnitude units (corresponding to the 2.5 and the 97.5 quantiles). The new M4 + catalogue with consistent Ml values for AFAD and KOERI shows magnitude residuals that cannot be explained by a Gaussian distribution. We also show a very good agreement between our new Ml value and the original Ml values of AFAD and KOERI, with median differences below 0.1 magnitude units.

Application of the enhanced horizontal gradient amplitude (EHGA) filter in mapping of geological structures involving magnetic data in southeast Nigeria

Lineament detector and depth estimation method involving modern aeromagnetic data were employed to study parts of the Obudu Plateau and Lower Benue Trough (southeast Nigeria) with the aim of mapping thermo-tectonic geologic structures and estimating sediment thicknesses. In this investigation, the enhanced horizontal gradient amplitude (EHGA) (applied to both simulated and real data) and tilt depth approaches were operated. The simulated magnetic model employing the EHGA detector generated sharp and properly defined edges of magnetic bodies with the capacity to place peaks over source borders. The tilt depth technique showed thin and thick sedimentations that vary from ∼ 500 to ∼ 1000 m and ∼ 1500 to ∼ 2500 m, respectively. The observed geologic structures trend mainly in the NW and NE, as well as minor NS directions. These structures, generated by the Younger Mesozoic Granitic intrusions of calc alkaline ring complexes, and the Santonian Abakaliki Anticlinorium serve as paths for super enriched hydrothermal fluids migration and deposition. The applied methods can be used to decipher the geologic structures in alike zones around the world.

Dynamic Response Analysis of Dual-Flow Channel Pump Station Structure under Water Pressure Pulsation

The RNG k-ε model turbulence model is used to carry out a CFD numerical simulation of the dual-flow channel pumping station. Through the model test, the accuracy of the numerical simulation of the dual-flow channel pump device is verified. Using the harmonic response analysis method, the water pressure fluctuating load calculated under different startup conditions under the design water level is applied to the pumping station. In this way, the dynamic response law of the pump station structure under the action of water pressure pulsation is studied. The calculation results show that the values of pressure pulsation in the drainage condition and the water diversion condition are relatively close, and the main difference is the difference in the water levels of the inlet and outlet water. Under different working conditions, the amplitude of the pumping station building basically shows the characteristics that the vertical amplitude is greater than the horizontal amplitude. The maximum dynamic displacement under drainage condition is greater than that under the diversion condition, and the maximum dynamic displacement appears at the control gate. Under the three working conditions, the maximum dynamic stress of each characteristic part of the pumping station building is low. The maximum total dynamic stress under the drainage condition is greater than that under the diversion condition.

Research on Dynamic Response and Construction Safety Countermeasures of an Adjacent Existing Line Foundation under the Influence of a New Railway Line

The excavation of a new high-speed railway causes the side slope adjacent to the existing line foundation to become airborne, and the excessive dynamic deformation or cumulative deformation caused by the dynamic load of trains will affect the normal service of the subgrade, even leading to its instability. To date, there are no relevant experimental data regarding this, and there is also a lack of corresponding specifications. The only available numerical simulation research results need to be verified in practice. Therefore, this study relies on the Shanghai–Nanjing intercity high-speed railway construction project adjacent to the existing Beijing–Shanghai line to carry out a subgrade dynamic response test to ensure the safe operation of the existing line. The test obtained the vibration displacement, frequency, acceleration, and other parameters of the existing subgrade construction in three stages: subgrade excavation, pile formation, and subgrade filling. From the test results: During the test period, the vertical surface vibration displacement and vibration acceleration have a certain attenuation along the depth direction. In the stage of subgrade excavation, the vibration displacement and vibration acceleration generated are the largest. The vertical vibration displacement amplitude reaches 1.9 mm, and the horizontal vibration displacement amplitude reaches 0.15 mm. The vibration frequency of the roadbed under the action of the train load is concentrated in the range of 0–50 Hz, and the vibration energy at the peak value is relatively large, which reflects the load action frequency of the train, and the peak value is mainly concentrated in the range of 20–40 Hz. These results show that the maximum vibration response peak appears in the subgrade excavation stage, that is, the most dangerous stage of the existing subgrade. The vibration acceleration and vibration displacement of each dynamic response parameter are important in that they reflect the dynamic performance of the subgrade and establish the index control standard, which can be used as a control index for roadbed dynamic stability monitoring. The dynamic test of the subgrade state provides data support for the reasonable opening of the construction skylight and the protection of the excavation slope. Taking into account the impact of piling vibration, technical measures such as static pressure, jumping construction, and setting up stress relief holes are adopted. The test results and engineering measures ensure the safe operation of the existing subgrade, and have important theoretical significance for guiding the construction of the new subgrade adjacent to the existing line.

Delineation of structural lineaments of Southeast Nigeria using high resolution aeromagnetic data

Abstract Structural lineaments of Southeast Nigeria were delineated using high-resolution aeromagnetic data. Advanced methods such as enhanced horizontal gradient amplitude (EHGA) involving a 3D model and tilt depth method (TDM) were used in this study. The simulated magnetic model involving the EHGA detector positioned peaks over source borders and created sharp and clear edges for magnetic sources. The TDM is a cutting-edge depth determination method revealing the depth of the contacts and thickness of sedimentary bodies that vary from ∼500 to ∼2,500 m and ∼3,000 to ∼5,000 m, respectively. Lineaments of the study area were extracted from the EHGA map. The structural map showed the dominance of short-ranged (∼0.29 to ∼1.48 km) linear magnetic anomalies. In addition, regional geologic structures (∼2.8 to ∼24.5 km) occur at the western flank of the study area. In general, these structures trend in the NE–SW, NNE–SSW, N–S, E–W, and NW–SE directions. They are indicators of subsurface faults, contacts, and tectonic structures of the thermo-tectonic events associated with Santonian Abakaliki Anticlinorium, Tertiary-Recent Ikom-Mamfe Rift, and structural deformations of the basement rocks associated with the Oban Massif.

Two-Dimensional Fast Multipole Indirect Boundary Element Method-Based Solution to P-Wave Scattering by a Mountain with Large-Scale Random Cracks in an Elastic Half-Space

In this study, the fast multipole indirect boundary element method (FM-IBEM) was adopted for solving the scattering problem of incident P-waves using a two-dimensional (2D) mountain terrain with large-scale random cracks. By adopting the FM-IBEM, this study resolves the bottleneck of the conventional boundary element method (BEM) for computing complex multi-degree-of-freedom models, and for the first time quantitatively analyzes the seismic wave scattering problem of large-scale narrow mountain cracks. After verifying the calculation accuracy, the horizontal and vertical displacement amplitudes of the mountain surface and its adjacent surface were accurately calculated. The results suggest the following: (1) Cracks significantly amplify the displacement amplitude of the mountain surface. The amplification mostly depends on the number of cracks and on the frequency of the incident P-wave. Compared with homogeneous mountains (no cracks), under the most unfavorable circumstances, the horizontal displacement is amplified more than 9.5-fold, while the vertical displacement is amplified more than 6.5-fold. (2) When the wave field passes through the crack area, a large amount of energy is trapped. Moreover, this energy is highly concentrated, which amplifies the local ground motion more than 7-fold. (3) The ground motion generated by the P-wave scattering by a mountain with large-scale random cracks exhibits a significant spatial difference. (4) The resonance of multi-order modes can emerge owing to large-scale random cracks. Compared with homogeneous mountains, the ground motion caused by the P-wave scattering by mountains with large-scale random cracks is much more severe in many cases. This phenomenon must be considered in practical seismic engineering applications.

A Novel Single Tube Semi-Active Tuned Liquid Gas Damper for Suppressing Horizontal Vibrations of Tower-like Structures

The purpose of this paper is to present a novel single tube semi-active tuned liquid gas damper (SA-TLGD) for suppressing horizontal vibrations of tower-like structures and to study its damping effectiveness. The main difference to the well-known state-of-the-art tuned liquid column damper (TLCD) is the special geometric shape of the developed SA-TLGD. Contrary to the TLCD, the presented SA-TLGD only consists of a single horizontal tube that is partially filled with water. A large deformable elastic membrane with neglectable stiffness is used as the interface between the liquid and the air. Both ends of the horizontal tube are sealed and the resulting gas spring is used as the restoring force and frequency tuning parameter, respectively. The developed SA-TLGD is a semi-active vibration damping device, where its natural frequency and magnitude of energy dissipation can be re-adjusted during operation. Due to the lack of any vertical tube parts, this new type of vibration absorber requires significantly less installation space compared to the classical TLCDs. The equations of motion of the SA-TLGD and the coupled main system are derived by the application of conservation of momentum. The procedure of optimal tuning of the SA-TLGD is presented, and computational numerical studies are performed to demonstrate the damper effectiveness. It is shown that the application of the developed SA-TLGD provides a large reduction in the maximum horizontal forced vibration amplitudes of tower like-structures and that its semi-active functionality enables the possibility of re-adjustment any time during the operation life of the structure.

Effect of equilibrium radial position on horizontal instability of middle single null divertor configuration in the iron core tokamak

The unique high-field side middle single null divertor configuration in the Joint-Texas Experimental Tokamak is attractive in studying detachment, impurity control, L-H transition, and negative triangularity. Its equilibrium configuration with a horizontally elongated (or flattened) poloidal cross section causes position instability and difficulty in equilibrium control. This work disassembles the vertical magnetic field of each group of poloidal field windings and calculates the field decay index (n-index) at different radial positions. It is found that the instability growth time τg of horizontal displacement increases as the equilibrium radial position of plasma moves outward, which is beneficial to the position control. The simulation and experiments verified the effect of equilibrium position on horizontal instability. The equilibrium position slightly outward from the geometric center of the vacuum chamber effectively decreases the horizontal displacement oscillation amplitude and guarantees the controllable horizontal displacement.

Practical Design of Machine Foundation Subjected to Harmonic Loading by Rotating Equipment with Varying Frequency

This paper presents a practical design of machine foundation subjected to varying harmonic loads. The dynamic analysis of machine foundation is performed using an analytical method. The varying harmonic loads are generated by varying the speed of the machine as per the performance requirements of the plant, which essentially results in operating the machine at or near the resonance. The vertical vibration and coupled horizontal and rocking vibrations are represented using Lysmer’s and Hall’s analogs, respectively. The equations of motions are formulated considering the vertical motion and coupled horizontal and rocking motion of the foundation soil system in the lumped parameter approach. The analytical formulation is capable of considering the moments generated due to the eccentricity of loads (i.e., static weights of the machine and foundation). A computer program is developed using FORTRAN to obtain the practical solutions for the machine foundation soil system. The maximum amplitudes of the vertical and horizontal displacements of the case study example are 22.5 and 110.68 μm, respectively, for the operating frequencies ranging from 2.5 to 12.1 Hz. The performance of the induced draught fan foundation is evaluated using the General Machinery Vibration Severity Chart, the guidelines given in the publication Foundations for Machines: Analysis and Design, and the American Concrete Institute standard ACI 351.3R-04. These charts and guidelines help in assessing the performance of the machine foundation system during operation of the plant. Based on the results, the performance of the machine foundation system is rated as “good” to “very good” and “fair” to “slightly rough” category based on the obtained vertical and horizontal amplitudes of the displacements respectively. Based on the measured data, it is noted that the evaluated performance parameters are well within the operating parameters of the machine foundation system.

Main structural lineaments of the southern Cameroon volcanic line derived from aeromagnetic data

The Cameroon Volcanic Line (CVL) is an African-only active alkaline intraplate feature that ranges in age from Oligocene to recent, with volcanoes crossing the oceanic-continental boundary. Because of its Cenozoic tectonic processes and magmatic features associated to seismic and volcanic activity, studies of the CVL geodynamic are of great importance. Despite its shear zone features, detailed structural geophysical studies of the southern CVL remain elusive. In this work, we use high-resolution airborne magnetic data to reveal geophysical signatures of the CVL. We apply a combination of derivative and phased filters and an improved cross-correlation approach to delineate geological structures of the southern CVL and propose an interpretation from aeromagnetic data. Derivative and phased filters highlight three distinct magnetic domains, with high positive and negative amplitudes. Rata Mount and Rumpi Hills, for example, show a NE-SE trend and a high magnetic amplitude. This finding might be explained by different types of rocks, consisting of the Upper Cretaceous basalt and sandstone sequences. The intensity of the enhanced horizontal gradient amplitude (EHGA) is well associated with geological features and its effects on a topographic relief. From the cross-correlation analysis, we successfully obtained the magnetization direction of a few specific anomalies.

Research on Dynamic Response Characteristics for Basement Structure of Heavy Haul Railway Tunnel with Defects

Based on the basic principle of thermodynamics, an elastoplastic damage constitutive model of concrete is constructed in this paper. The model is realized and verified in FLAC3D, which provides a solid foundation for the study of dynamic response and fatigue damage to the base structure of a heavy haul railway tunnel. The dynamic response and damage distribution of the base structure of a heavy-duty railway tunnel with defects were numerically simulated by the concrete elastic-plastic damage constitutive model. Then, by analyzing the response characteristics of the tunnel basement structure under different surrounding rock softening degrees, different foundation suspension range and different foundation structure damage degree are determined. The results show the following: (1) The elastoplastic damage constitutive model of concrete can well describe the stress–strain relationship of materials, especially with the simulation results of post peak softening being in good agreement with the test results, and the simulation effect of the unloading–reloading process of the cyclic loading and unloading test also meet the requirements. (2) The initial stress field and dynamic response of the tunnel basement structure under the action of train vibration load are very different from the ideal state of the structure design when the surrounding rock of the base is softened, the base is suspended, or the basement structure is damaged. With the surrounding rock softening, basement hanging, or basement structure damage developing to a certain extent, the basement structure will be damaged. (3) The horizontal dynamic stress amplitude increases with the increase in the softening degree of the basement surrounding rock. The horizontal dynamic stress of the measuring point increases with the increase in the width of the hanging out area when the hanging out area is located directly below the loading line. When the degree of damage to the basement structure is aggravated, the horizontal dynamic tensile stress of each measuring point gradually decreases. (4) The maximum principal stress increment increases with the increase in the fracture degree of the basement structure, while the minimum principal stress increment decreases with the increase in the fracture degree of the basement structure, but the variation range of the large and minimum principal stress increments is small. The research results have important theoretical and practical significance for further analysis of the damage mechanism and control technology of the foundation structure of a heavy haul railway tunnel with defects.

Experimental and numerical investigations on attenuation response of machine foundations under vertical excitation

ABSTRACT The attenuation response from a series of block vibration tests performed on a model square machine foundation at a site near IIT Kanpur, India, is reported in this paper. The dynamic response at different locations from the vibration source is measured for a wide range of frequencies. The observed attenuation response is compared with the analytical and the finite element (FE) solutions to bolster the experimental findings. A parametric study is conducted utilising the FE analysis to predict the surface wave mitigation characteristics in various soils. It can be observed that the surface waves dominate the attenuation characteristics at the far-field locations and attenuate at a faster rate in soft soils compared to stiff soils. The material and the geometric damping characteristics of the surface waves influence the attenuation characteristics of horizontal and vertical vibrations at the far-field pick-up points. The attenuation characteristics of horizontal and vertical amplitude responses are found to differ significantly. Curve fitting and regression analyses are also performed to develop simplified design expressions to predict the attenuation response of horizontal and vertical vibrations. The proposed design expressions compare well with the values reported in the literature and can be utilised by practicing engineers.

Delineation of structural lineaments of the Southwest Sub-basin (East Vietnam Sea) using global marine gravity model from CryoSat-2 and Jason-1 satellites

In recent years, the analysis of satellite gravity data is used as a powerful tool for geologic mapping. This study is based on various filtered maps of Bouguer gravity anomaly data of the Southwest Sub-basin (East Vietnam Sea) to delineate its main structural lineaments. The effectiveness of modern filtering methods such as normalized analytical signal, improved version of tilt angle and enhanced horizontal gradient amplitude has been estimated with synthetic gravity anomalies before applying to the gravity data of the Southwest Sub-basin. For synthetic examples, the results show that the enhanced horizontal gradient amplitude not only provides edges with high resolution but also prevents spurious edges in the output maps. For real case, the obtained structural map is consistent with many faults already recognized in the Sub-basin, and the results provide new information leading to a better understanding of the structural framework and tectonic setting of the area.

Effects of aerodynamic coupling and non-linear behaviour on galloping of ice-accreted conductors

Wind action on ice-covered transmission lines causes galloping, which is a problem because it can introduce interphase short circuits and cause fatigue of the cross-arms of the power line’s towers and insulators. The galloping phenomenon is characterised by a combination of large-amplitude, low-frequency vertical, horizontal, and torsional oscillations. To better understand the dynamic responses of vertical, horizontal and torsional 3-degree-of-freedom (DoF) galloping on four-bundled conductors, time–history analyses were conducted for 2D systems of varying DoFs and frequency ratios. The fundamental characteristics of the conductor’s non-linear 1-DoF vertical response were analysed via time–history analysis, indicating that large oscillations were caused by inclusion of an angular range of relative angle of attack with a high negative lift-coefficient slope. By considering the energy balance of the vertical motion over one oscillation period, we estimated the stable and unstable limit-cycle amplitudes. Then, by comparing the results of the 1-, 2-, and 3-DoF systems, we clarified the effect of aerodynamic coupling on 3-DoF galloping. The oscillation types in the 3-DoF systems were categorised as vertical–horizontal 2-DoF coupling oscillations, vertical–torsional 2-DoF coupling oscillations, and vertical 1-DoF oscillations according to the stationary torsional angle. Finally, we indicated the coupling effects on vertical oscillation by considering the energy balance of the vertical motion with the defined amplitudes and phase differences of the horizontal and torsional motions. The vertical amplitude of the vertical–horizontal 2-DoF coupling oscillation can become very large if the horizontal amplitude increases and the phase difference between horizontal and vertical displacements approaches 180°. Meanwhile, the range of the stationary torsional angle in which the vertical–torsional 2-DoF coupling oscillation occurs becomes wide as the phase difference between the torsional and vertical displacements approaches 90°. However, without horizontal motion, the vertical amplitude has a limited value, even if the torsional amplitude becomes large.

Eye movement patterns and reading ability in children.

Eye movements are integral to the reading process. This study characterised the eye movement patterns of children differentiated by their reading ability, while completing a saccadic eye movement test with irregular target spacing (Development Eye Movement (DEM) test) using a novel eye movement classification algorithm. Participants included 196 Grade 2 Australian schoolchildren (mean age: 7.9±0.3years) who completed a computerised version of the DEM test, while their eye movements were recorded (Tobii TX300 eye-tracker). Children also completed a standardised reading comprehension test, which categorised them into below average and average or above reading ability groups. A novel eye movement classification algorithm was developed that considered the vertical and horizontal eye movements of each child. Compared to children with average or above reading ability, the below average reading group displayed poor vertical eye movement control, demonstrated by a significantly greater proportion of interline eye movements (vertical eye movements away from the current line) (p<0.001). Differences in horizontal eye movements were also observed, with below average readers demonstrating a smaller proportion of expected forward saccades (p<0.001) (within-line forward saccades with horizontal amplitude between the minimum and maximum horizontal spacing between digits), while this group also displayed longer fixation durations (p=0.001). The below average reading group demonstrated significantly poorer results on all standard DEM metrics than the average or above reading ability group: horizontal subtest time (p<0.001), vertical subtest time (p=0.004) and ratio (p=0.004). Children exhibiting below average reading ability were poorer at maintaining control of vertical (interline), as well as horizontal, eye movements compared to children with average or above reading ability. Future studies should explore the mechanisms underlying these differences, particularly in vertical eye movements, given that reading paragraphs (involving multiple lines of text) requires accurate eye movements in both the vertical and horizontal direction.

Variable elliptical vibrating screen: Particles kinematics and industrial application

Traditional vibrating screen usually adopts the linear centralized excitation mode, which causes the difficulty in particles loosening and low screening efficiency. The variable elliptical vibrating screen (VEVS) trajectory is regulated to adapt the material mass along the direction of the screen length, improving the particles distribution as well as the screening efficiency. In this work, a theoretical model was developed for analyzing the screen surface motion law during VEVS-based screening process. An equation was obtained to show the relationship between the horizontal amplitude and the vertical amplitude. The materials kinetic characteristics were studied by using high-speed camera during screening process. Compared with equal-amplitude screen (EAS), the material moving velocity was increased by 13.03% on the first half but decreased by 3.52% on the second half, and the total screening time was reduced by 9.42% by using VEVS. In addition, −6 mm screening test was carried out. At the length of VEVS equaled to 1.2 m, the screening efficiency and the total misplaced material content were 92.50% and 2.90%, respectively. However, the screening efficiency was 89.91% and the total misplaced material content was 3.76% during EAS-based screening process. Furthermore, when external moisture is 5.96%, the screening efficiency of VEVS could reach 86.95%. The 2TKB50113 type VEVS with double-layered screen surface used in Huoshizui Coal Mine was 5.0 m in width and 11.3 m in length. The areas of single layer and double layer were 56.5 and 113 m2, respectively. In industrial production, the processing capacity was 2500–3000 t/h and the screening efficiency was larger than 90%.

Evaluation of horizontal to vertical spectral ratio and standard spectral ratio methods for mapping shear wave velocity across anchorage, Alaska

The use of horizontal to vertical spectral ratios (HVSR) of earthquake ground motions has become a standard technique to characterize sites, especially those lacking subsurface measurements. Several studies have developed relationships between HVSR results and time-averaged shear-wave velocity in the upper 30 m (VS30). Other studies have utilized standard spectral ratios calculated from horizontal ground motion Fourier amplitude spectra to estimate VS30. Anchorage, Alaska (USA), has a network of strong-motion recording stations, many of which have no site-specific subsurface characterization. This study compares measured VS30 and HVSR results from 18 strong-motion stations to four regional models developed by others. A relationship between the 1 Hz band-averaged (0.5–2.5 Hz) spectral amplification results and VS30 is presented. VS30 estimates for the strong-motion stations are made, and a regional model is developed between HVSR and VS30, both in terms of fpeak (the frequency of the peak HVSR amplitude) and Apeak (the amplitude of the peak). In addition to the regional model, additional VS30 data from other sites in Anchorage, including 19 downhole VS30 measurements and 22 microtremor VS30 estimates from others, are used with the strong-motion station VS30 estimates to develop a VS30 contour map of Anchorage. The contouring represents the spatial distribution of the site classes of the local building code, which are based on VS30. This map may be incorporated into planning documents for future developments in the city.

Horizontal UHS Amplitudes for Regions with Deep Soil Atop Deep Geological Sediments—An Example of Osijek, Croatia

In this paper, we demonstrate how UHS-based seismic microzonation can be applied in low-to-medium seismicity areas with deep local soil and deep geological deposits under the local soil. The case study area surrounds the city of Osijek, Croatia, which is in the south–central region of the Pannonian Basin. New frequency-dependent scaling equations are derived, and the empirical response spectra are compared to the spectra of real strong motions in the surrounding region. Empirical calculations for deep soil atop deep geological strata show a 37% reduction in short-period spectral amplitudes when compared to rock locations. This demonstrates that local soil amplification is mitigated by energy dissipation in deep soils. For vibration periods longer than 0.3 s, spectral amplitudes are being amplified. This amplification goes up to 2.37 times for vibration periods around 0.5 s. UHS spectra for Osijek are computed using regional seismicity estimates, data on local soil and deeper geological surroundings, and newly created regional empirical equations for scaling various spectral amplitudes. UHS amplitudes for Osijek are also compared to the Eurocode 8 spectra for ground type C. The results show that ratios of the maximum UHS amplitudes to PGA values are up to 46% larger than the corresponding 2.5 factor that is recommended by Eurocode 8 for horizontal spectra. The UHS results might be viewed as preliminary for Osijek and regions with similar seismicity and local soil and deep geology conditions. When the number of regional strong-motion records grows many times beyond what it is currently, it will be feasible to properly calibrate the scaling equations, resulting in more reliable and long-term UHS estimations for the area under consideration.

Subsurface structural mapping from high-resolution gravity data using advanced processing methods

The study area has a complex geological structure and is studied for mapping the density interfaces using geophysical techniques. However, it has not been studied for mapping geological structures, such as contacts and faults that appear as lineaments in gravity data. In this study, the lineaments in the area have been delineated using Bouguer gravity anomaly data, though some modern processing methods, such as horizontal gradient amplitude (HGA), tilt angle of horizontal gradient amplitude (THGA), and enhancement of horizontal gradient amplitude (EHGA). Most of the identified lineaments are trending in the NW–SE direction and some WE-trending lineaments in the southeastern region. This study provides new information for a better understanding of the structural framework and tectonic setting of the Thua Thien Hue area.

Cyclic strength of loose anisotropically-consolidated calcareous sand under standing waves and assessment using the unified cyclic stress ratio

Progressive and standing waves can produce instability of the seabed and seabed-supported marine structures. In this paper, the stress paths induced by standing waves were deduced to provide a theoretical basis for laboratory element tests to establish the cyclic behavior of marine sediments, which can serve to improve the understanding of seabed liquefaction triggering and its consequences. The cyclic response of loose, isotropically- and anisotropically-consolidated (IC and AC, respectively) calcareous sand under the stress paths derived for standing waves was examined using hollow cylinder torsional shear (HCTS) tests. The stress paths corresponding to standing waves are a vertical line, horizontal line, and ellipse, in a coordinate system consisting of the axial stress difference and the horizontal shear stress, for a soil element located at the nodes, antinodes, and intermediate horizontal positions, respectively. The phase difference, θ, between axial stress difference and horizontal shear stress appears to range from −45° ~ 7° for wave and seabed characteristics representative of the North Sea. The ratio of axial stress difference and horizontal shear stress amplitudes, λ, varies in the real number field. The experimental results indicated that the failure modes of IC and AC specimens are cyclic mobility and residual deformation failure, respectively, irrespective of the stress paths imposed. With the same consolidation state and cyclic stress ratio, CSR, the number of cycles to failure, Nf, is strongly affected by θ and λ. The unified cyclic stress ratio, USR, is proposed to establish a single USR-Nf curve that can suitably describe the general cyclic strength of the calcareous sand specimens under different stress paths for a given consolidation stress ratio. The proposed USR enables estimation of the cyclic strength of IC and AC soils under complex stress paths based on the CSR-Nf curve obtained from conventional cyclic torsional shear or triaxial tests.