Frequency Of Seismic Waves Research Articles

A seismic metamaterial concept with very short resonators using depleted uranium

Depleted uranium (DU) is a metal of very high mass density and, other than a few specialized uses, is treated as a waste product of the uranium enrichment process. To take advantage of its high mass density, we propose a novel application of this metal in elastic/seismic metamaterials. Such use can not only broaden the range of design possibilities for elastic metamaterials but can also give more meaning to the disposition of DU. Five different design concepts are modeled and analyzed using numerical techniques. The band structure comparison of the concepts shows that very low-frequency band gaps in the range of seismic wave frequencies can be achieved with very simple configurations, smaller geometries, and feasible placing arrangements.

Effect of tunnel depth on the amplification pattern of environmental vibrations considering the seismic interaction between the tunnel and the surrounding soil

The amplitude and frequency of seismic waves caused by earthquakes change as they propagate in the subsurface environment. This change is further influenced by the presence of underground structures and the kinematic interaction between the structure and the propagating seismic wave. Analysis of ground motion and subsurface propagation of a seismic wave in the presence of an underground structure needs to include appropriate ground input motion parameters. Thus, to ensure security of important engineering structures and to prevent environmental damage under earthquake excitation the dynamic response of the vibrating underground structure and subsurface wave propagation interaction problem needs to be analyzed carefully. The aim of this study is to evaluate the results of the amplification effect on free field motions and the underground structure considering the tunnel-soil structure using numerical tools. The 2-D finite element method was used as a numerical model to determine the magnification effect of seismic excitation with various frequencies on surface vibration in the presence of a tunnel structure. The analysis includes various local soil conditions with different shear wave velocity were considered to evaluate the seismic behavior of the vibrating tunnel-soil system and its environmental impact. To evaluate the change in amplification patterns, the analysis was first performed on the free field and then the results were compared with the case where a tunnel structure was present. Then, the similar influences were investigated by using the numerical tool considering other parameters such as tunnel depths and soil characteristics. Results indicate that the presence of underground structure amplified the seismic vibrations on the free field and tunnel depending on the frequency of the external load and the local soil condition.

An underground barrier of locally resonant metamaterial to attenuate surface elastic waves in solids

The low frequency of seismic waves severely limits the regulation of wave propagation in earthquake protection engineering applications. In recent years, locally resonant metamaterials have been introduced for seismic wave attenuation. A barrier based on locally resonant metamaterials consisting of rows of wells is proposed to reduce the transmission of Rayleigh waves during propagation, achieving earthquake protection. First, comparisons are made between the wells of the metamaterial, empty wells, solid steel wells, and a continuous steel wall. It is evident that locally resonant metamaterials exhibit better performance than that of the other materials. Simulations of the relationships between the attenuation of Rayleigh waves and the depth, number of rows, and working frequency of the wells are presented. With a barrier of ten rows of wells, where the diameter of each well is less than one-twentieth of the wavelength of the Rayleigh wave and the depth of the wells is nearly four-fifths of the wavelength, the maximum attenuation reaches up to 16.2 dB when all the wells share the same working frequency, and the bandwidth is broader, but the maximum value is less when the rows have different working frequencies. Depending on the demand for a higher value or a broader bandwidth of the Rayleigh wave attenuation, this barrier promotes flexible and achievable improvements by adding rows or decentralizing the working frequencies of the wells. The vast potential of seismic wave attenuation from locally resonant metamaterials is anticipated in the future.

Research of laminated rubbers influence on the LNG-tank seismic resistance

The article developed a finite-element model of a tank for storing liquefied natural gas. The influence of the damping coefficient of laminated rubbers on the movement of the tank and the acceleration of the stored product at different frequencies of seismic waves is numerically studied. Graphic dependences of the displacement and acceleration of the structure along the height of the wall are established.

Shaking table test study on the functionality of rubber isolation bearing used in underground structure subjected to earthquakes

Steel-reinforced rubber isolation bearing has been widely adopted in ground structures to improve structural seismic resistance property. However its use in underground structures is not elaborately examined. Through a series of shaking table tests, the functionality of isolation bearings connected to structural intermediate columns' feet in underground structure during seismic actions is investigated, compared with the dynamic response characteristics of model structure with general reinforced concrete columns. Result analysis shows that dynamic reaction of underground structure is fundamentally determined by soil motions, the isolation bearing can not shift structural fundamental period away from the prominent frequency of seismic waves to enhance structural seismic resistance capacity like the way in the case of ground structures. However, as the soil-structure interaction changes a lot along structure height, isolation bearings can effectively obstruct lateral shear forces developed in top structural part from transferring into down structural part, which will avoid force concentration in low structural part, making structural deformation distributed uniformly along structure height in comparison with the deformation in structure without isolation device. Other changes of underground structural dynamic reactions to earthquakes brought out by isolation device will be also detailed.

A seismic-shielding structure based on phononic crystal

In this paper, a seismic-shielding structure is presented based on phononic crystal, which is now used to control acoustic waves. An earthquake-proof barrier of seismic waves can be built by filling up the structure under the ground around the building that we want to protect. When the frequency of seismic waves falls into the band gaps of the structure, the seismic wave can be blocked. Herein, the frequency band gaps of the structure is calculated theoretically, and the influence of geometric and material parameters on the frequency band gaps is analyzed.

Colliding Beams Focus Displacement Caused by Seismic Events

The Earth surface inclinations recorded by the Precision Laser Inclinometer have been transformed to vertical oscillations using a specifically developed method. A method to calculate the space displacement of collider beams focuses is proposed to evaluate the effects of the surface waves propagation, taking into account: the length of the region of the beam focusing for collisions, the seismic wave frequency and the wave speed dependence on the frequency. It is shown that the beams focus divergence is measurable: for the LHC, with a 40-m long beam focusing path for collisions, in the frequency range above 1 Hz for the seismic surface wave; for the CLIC (first stage), with a 1.9-km long beam focusing path for collision, in the frequency range [0.1 Hz, 0.5 Hz], typical range of the micro-seismic peak. The data obtained shows the necessity of monitoring the seismic activity by using a network of Precision Laser Inclinometers.

Shaking table test on seismic response characteristics of prefabricated subway station structure

This paper is based on the research and development of the first fully prefabricated subway station in Changchun as the engineering background. Through the first large-scale shaking table test of a fully prefabricated subway station structure in China, the macroscopic phenomena of the model system in an actual earthquake occurrence were qualitatively reproduced. Based on the macroscopic phenomena of video surveillance, the seismic responses of the model structure were graded and evaluated. The analysis showed that under the same earthquake action, the seismic responses of the lower layer of the station were stronger than those of the upper layer, the Beijing wave was the strongest, the Taft wave was the second strongest, and the Mingshan wave was the weakest. The acceleration and lateral displacement of the model foundation and the acceleration, structural strain, joint deformation and soil pressure of the model structure were tested and analysed. The results showed that the closer the main frequency of seismic wave was to the main frequency of the model system, the more intense the seismic response was. With an increase in seismic intensity, obvious phenomena of low-frequency amplification and high-frequency filtering occurred. Shear deformation occurred laterally in the model foundation, and the peak displacement appeared obviously asymmetrical in the process of left and right lateral displacement. The existence of the underground structure obviously changed the propagation law of the seismic wave in the model foundation, and the closer the structure was, the more significant the difference was. The strength of the mortise-groove joint was better than that of the prefabricated component, which showed excellent integrity and mechanical properties. The model station structure had excellent cooperative work and deformation resistance properties. When rare earthquake loading occurs, the vault would gradually degenerate into a three-hinged arch mechanism and maintain a relatively stable state.

Fractional integration of seismic wavelets in anelastic media to recover multiscale properties of impedance discontinuities

Multiscale seismic attributes based on wavelet transform properties have recently been introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium. We extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly. The method assumes an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a Gaussian derivative function (GDF). We highlight a quasi-conservation of the Gaussian character of the wavelet during its propagation. We found that this shape can be accurately modeled by a GDF characterized by a fractional integration and a frequency shift of the seismic source, and we establish the relationship between these wavelet parameters and [Formula: see text]. Based on this seismic wavelet modeling, we design a time-varying shaping filter that enables making constant the shape of the wavelet allowing retrieval of the wavelet transform properties. Introduced with a homogeneous step-like reflector, the method is first applied on a thin-bed reflector and then on a more realistic synthetic data set based on an in situ acoustic impedance sequence and a high-resolution seismic source. The results clearly highlight the efficiency of the method in accurately restoring the multiscale seismic attributes of complex seismic reflectors in anelastic media by the use of broadband seismic sources.

Analysis of coal seam thickness and seismic wave amplitude: A wedge model

Coal seam thickness is of great significance in mining coal resources. The focus of this study is to determine the relationship between coal seam thickness and seismic wave amplitude, and the factors influencing this relationship. We used a wedge model to analyze this relationship and its influencing factors. The results show that wave interference from the top and bottom interfaces is the primary reason for the linear relationship between seismic wave amplitude and wedge thickness, when the thickness of the wedge is less than one quarter of the wavelength. This relationship is influenced by the dominant frequency, reflection coefficients from the top and bottom boundaries, depth, thickness, and angle of the wedge. However, when the lateral shift between the reflected waves is smaller than the radius of the first Fresnel zone, the wedge angle and change in lithology at the top and bottom layers are considered to have little effect on the amplitude of the interference wave. The difference in the dominant frequency of seismic waves can be reduced by filtering, and the linear relationship between amplitude and coal thickness can be improved. Field data from Sihe coal mine was analyzed, and the error was found to be within 4% of the predicted seismic wave amplitude. The above conclusions could help predict the thickness of coal seam by seismic amplitude.

Influence of Saturant on Seismoelectric Coupling Response of Porous Media

The seismoelectric coupling phenomenon in porous medium saturated with gas and water was studied numerically. The numerical model was formulated based on Pride's theoretically developed seismoelectric coupling coefficient that describes conversion of seismic energy into electromagnetic radiation. The conversion is complex function of physical, electrical and poroelastic properties of the porous medium and the saturant. In this study, a porous medium that is partially saturated with water is considered. Pore spaces that are not saturated with water are considered to be filled with gas. The gas phase is methane. The water saturation was varied from 0.2 to 0.9. The physical and electrical properties of both phases are determined at a temperature of 325 °K. The porosity and permeability of the porous medium is 0.2 and 500 mD, respectively. The porous medium in this study is isotropic. Zeta potential was estimated using an empirically derived correlation. At 0.001 mol/lit salinity, zeta potential is 66.7 mv. The numerical study result shows that at a fixed seismic wave frequency, lower water saturation results in higher seismoelectric coupling coefficient. When water saturation increases, the seismoelectric coupling coefficient decreases. However, the rate of decline is lower at higher seismic frequency. The rate of decline at 10 kHz is 1.38 nV/Pa compared to 4.35 nV/Pa at 100 kHz. Higher frequencies result in stronger nonlinearities, which causes higher mechanical energy dissipation. As such, the result obtained in this study is consistent with what is normally expected when mechanical wave propagates through a porous media.

Seismic responses of an isolated concrete rectangular liquid-storage structure

To study the seismic response of a liquid-solid coupling in an isolated concrete rectangular liquid-storage structure under small amplitude sloshing, a three-dimensional model of the isolated concrete rectangular liquid-storage structure was established based on the assumption that the concrete is considered to be a linear elastic material. The seismic responses of the isolated concrete rectangular liquid-storage structure with the same liquid sloshing height under different seismic intensities and different liquid heights under the same earthquake wave were studied. The results show that the seismic responses of the rectangular liquid-storage structure are different in the cases of small amplitude sloshing and linear elastic material with different seismic intensities due to the effects of the seismic wave frequency domain and time domain characteristics. At the same liquid height, the wall displacement, the liquid sloshing height and the equivalent stress of the isolated concrete rectangular liquid-storage structure are increased as the seismic intensity increases. The liquid height has a certain effect on the seismic responses of the liquid-storage structure, and when the liquid height is lower, the peak values of the liquid sloshing height, the wall displacement and equivalent stress are greater.

Numerical Study of Frequency-dependent Seismoelectric Coupling in Partially-saturated Porous Media

The seismoelectric phenomenon associated with propagation of seismic waves in fluid-saturated porous media has been studied for many decades. The method has a great potential to monitor subsurface fluid saturation changes associated with production of hydrocarbons. Frequency of the seismic source has a significant impact on measurement of the seismoelectric effects. In this paper, the effects of seismic wave frequency and water saturation on the seismoelectric response of a partially-saturated porous media is studied numerically. The conversion of seismic wave to electromagnetic wave was modelled by extending the theoretically developed seismoelectric coupling coefficient equation. We assumed constant values of pore radius and zeta-potential of 80 micrometers and 48 microvolts, respectively. Our calculations of the coupling coefficient were conducted at various water saturation values in the frequency range of 10 kHz to 150 kHz. The results show that the seismoelectric coupling is frequency-dependent and decreases exponentially when frequency increases. Similar trend is seen when water saturation is varied at different frequencies. However, when water saturation is less than about 0.6, the effect of frequency is significant. On the other hand, when the water saturation is greater than 0.6, the coupling coefficient shows monotonous trend when water saturation is increased at constant frequency.

Investigation into dynamic response of regional sites to seismic waves using shaking table testing

This study addresses the changes in acceleration, pore water pressure and Fourier spectrums of different types of seismic waves with various amplitudes via large-scale shaking table tests from two sites: a sand-containing regional site and an all-clay site. Comparative analyses of the test results show that the pore water pressures in sand-soil layers of the regional site initially increase and then decrease as the amplitudes of the seismic accelerations increase. The actions of the vertical and vibrational seismic waves contribute to greater pore water pressures. The amplification coefficient of the sand-layer regional site becomes smaller as the seismic waves grow stronger, so that both sites are capable of filtering high frequencies and amplifying low frequencies of seismic waves. This is more apparent with the increase in the peak value of the acceleration, and the natural vibration frequencies of both sites decrease with the transmission of the seismic waves from the basement to the ground surface. The decreasing frequency value of the sand-containing regional site is smaller than that of the all-clay site.

Seismic isolation of two dimensional periodic foundations

Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

ARTIFICIAL SEISMIC SHADOW ZONE BY ACOUSTIC METAMATERIALS

We developed a new method of earthquake-proof engineering to create an artificial seismic shadow zone using acoustic metamaterials. By designing huge empty boxes with a few side-holes corresponding to the resonance frequencies of seismic waves and burying them around the buildings that we want to protect, the velocity of the seismic wave becomes imaginary. The meta-barrier composed of many meta-boxes attenuates the seismic waves, which reduces the amplitude of the wave exponentially by dissipating the seismic energy. This is a mechanical method of converting the seismic energy into sound and heat. We estimated the sound level generated from a seismic wave. This method of area protection differs from the point protection of conventional seismic design, including the traditional cloaking method. The artificial seismic shadow zone is tested by computer simulation and compared with a normal barrier.

Influence of seismic wave frequency on the quality of the landslide surface exploration in the light of numerical modeling

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Shaking Table Test on Seismic Response of Isolated Bridge

In order to investigate isolation effectiveness on seismic performance of the continuous rigid frame bridge, shaking table test with nine sub-tables on 1/10 scaled reinforced concrete rigid frame bridge specimen was performed. The experimental results demonstrate that isolation devices provide flexibility to transform natural period of the scaled model, and additional it can improve the ability of energy dissipation when lead is used. The initial first frequency is 8.17Hz for plate-type rubber bearing and 9.12Hz for leading rubber bearing. The plate rubber bearing and lead-rubber bearing are quite sensitive to seismic wave frequency. The use of various isolation devices affects response of the bridge model. The results show that the more difference in the isolation devices, the more difference in response. Moreover, isolation effect of lead-rubber bearing show obviously more advantage than the one of plate-type rubber bearing, especially in controlling responses of the bridge during major earthquakes.

Analysis and Calculation of Seismic Performance for UHV Equipment of HGIS

In order to analyze and understand the seismic performance of UHV HGIS, and further improve it, the analysis of dynamic characteristics and seismic response spectra for 1100kV HGIS was carried out in four kinds of seismic waves, and then acquired structural frequencies and mode features. The situation that the natural frequency of UHV equipment and the main frequency of seismic wave were so similar that quasi resonance occurred was considered in the process of analysis. The calculation is conducted by the string of modulated wave that includes three sinusoidal-resonant waves and five sinusoidal-resonant modulated waves to analyze mechanical strength and seismic performance of integral structure. The results show that 1100kV HGIS under those seismic waves has certain safety margin, provide effective data for analysis of seismic performance of UHV equipment.

Laws of Influence upon Dynamic Response of High Rock Slope by Seismic Wave Frequency

On the basis of seismic wave recorded by Wolong Measuring Station in Wenchuan Earthquake occurred on May 12, 2008, and taking a high rock slope (about 1397m in height) at the bank of Zipingpu Reservoir as the specific example, analyses have been made, with Plaxis dynamical simulation analysis program, on characteristics of influence upon acceleration time history, shear strain distribution, principal stresses distribution and stability of high rock slope by original seismic wave, and seismic wave with frequency expanded by 1.5, 2 and 3 times, respectively. Results of the analyses demonstrate that dynamic response characteristics of the slope top are notably influenced by multiplication factor of seismic wave frequency. As far as the real slope in this article is concerned, it generally presents a gradual decrease of PGA of the top of high rock slope, reduction of slope body shear strain and a corresponding drop of dynamic response of slope body as a whole, with the increase of seismic wave frequency.