Frequency Of Seismic Waves Research Articles

Vibration Analysis of the Bow Bridge With and Without the Soil Foundation

Abstract. Earthquakes can impart the phenomenon of resonance, where the frequencies of seismic waves align with a bridge's natural frequency, causing amplification of vibrations that can lead to structural failures. Aiming to accurately predict potential vulnerabilities posed to the bridge when subjected to earthquakes, this research presents a vibration analysis of the Bow Bridge. Two models, which simulate the Bow Bridge with and without soil foundation, are conducted to investigate the bridges natural frequencies and mode shapes under soilless and soiled conditions. The research result shows that the average vibration frequency in a soiled environment is much lower than that in a non-soil environment, intuitively proving the mitigation of soil environment to bridges vibration frequencies. Based on the agreeable data output, this research demonstrates the feasibility of modeling in the prediction of practical construction.

A new seismic wave input method for canyon sites based on the finite element method-indirect boundary integral equation method

The seismic input is the basis for the seismic safety analysis of dams, but current seismic input methods have not reasonably considered the influence of canyon scattering effects on the dynamic response of dams. In this paper, the total motion field of the canyon is deconstructed into the free field of a uniform half space and the scattering field of the canyon and they are obtained separately. The indirect boundary integral equation method (IBIEM) is used to determine the scattering field of the canyon, which is superimposed with the free field to obtain the seismic ground motion field (total motion field) of the canyon. The accuracy of the total motion field of the canyon is verified through reference solutions. In the finite element analysis of seismic ground motion field in the canyon, the total motion field at the truncation boundary of the canyon foundation is transformed into the equivalent seismic input loads and the interior of the canyon are simulated using the finite element method (FEM). Then, based on the wave input for the free field combined with the viscoelastic artificial boundary, a new wave input method for the total motion field combined with the viscoelastic artificial boundary is established. The seismic wave input method based on the finite element-indirect boundary integral equation method is applied to numerically determine the seismic response of a trapezoidal canyon. The differences in the seismic response of the canyon under free-field input and total motion field input are discussed. The results show that there is a certain deviation between the displacement and waveform obtained from the free-field input and the solutions obtained from the indirect boundary integral equation method. There is a large error for a large angle of incidence, and the errors increase with increasing seismic wave frequency. When the incident angle is 60°, the maximum error in the frequency domain reaches 92.3 %, and the maximum error in the time domain reaches 250 %. The displacement amplitude and waveform of the canyon obtained from the total motion field input showed agreement with the results of the indirect boundary integral equation method. The wave input method established in this paper has high calculation accuracy and reasonably considers the scattering effect of canyons, which provides a basis for more accurate predictions of the seismic response of dams on canyon foundations.

Shaking table tests for seismic response of jack-up platform with pile leg-mat foundation on sandy seabed

The pile leg-mat foundation is a novel composite foundation designed for jack-up offshore platforms. The seismic response of such foundations in sandy seabeds is an issue that requires significant attention. In this study, shaking table tests were conducted under various input seismic waves to investigate the dynamic response of a seabed platform system subjected to seismic loads. The effects of the peak ground acceleration (PGA), seismic wave frequency, wave type, pile leg insertion depth, and pile length on the response of the seabed platform system were investigated. The results indicated that as the PGA increased, the acceleration response of the soil and platform model increased, increasing the accumulation of excess pore water pressure and the horizontal displacement of the platform model. The acceleration and horizontal displacement responses of the seismic wave with lower frequencies were higher than those with higher frequencies. The peak acceleration amplification factors under the measured and regular seismic waves showed significant differences, with the dynamic response of regular waves to the platform model being pronounced. Under seismic waves with low PGAs, the horizontal displacement of the platform model decreased with increasing pile leg insertion depth or pile length.

Instrumentation of the Nigeria network of seismological stations

“Living in fear of Nigeria biggest Earthquake” is a sub-heading of the Punch daily newspaper of Nigeria, dated, 21st of August, 2016, reported the earthquake/tremor recently witnessed in the ancient town of Saki, accompanied by a series of aftershock events that lasted for about three (3) months (March/May, 2016) southwest Nigeria[1]. Similarly, roughly five (5) years later, another series of earthquakes/tremors occurred again in Saki town, which was reported by an online news vendor named “Ripples Nigeria” dated September 8, 2021, under the sub-heading of “earth tremor rocks Saki in Oyo state”[2]. However, these events were not captured nor recorded by any of the functional seismological stations in Nigeria. The nearest seismological station located at the Obafemi Awolowo University (OAU) Ile-Ife, also failed to capture the events. We therefore seek to examine the instrumentation of the Nigerian National Network of Seismographic Stations. This is necessary to understand the functionalities and the capabilities of the deployed seismometers in each of the seismic stations. Therefore, we evaluated the bandpass limit of the seismic wave frequency for the respective seismic stations in Nigeria through the computation of the amplitude-frequency response curve, phase response curve, and count to cm/sec.

Acoustic wave propagation and scattering in visco-acoustic medium: Integral equation representation and De Wolf approximation

A visco-acoustic medium is an approximate representation of the absorption and attenuation characteristics of the actual earth medium, which will cause energy attenuation and velocity dispersion of seismic waves. The propagation law of scattered waves in viscoelastic media can be revealed through seismic wave forward simulation. However, the numerical simulation of scattered waves in a visco-acoustic medium using the De Wolf approximation method based on the Lippmann-Schwingr (L-S) equation has not been studied. Therefore, based on the Futterman dispersion relation, the mathematical expression of the integral equation of acoustic wave propagation and scattering in the visco-acoustic medium is derived. We combine the De Wolf approximation with the quality factor Q. The thin slab approximation and screen approximation methods are two realizations of the De Wolf approximation. The thin slab approximation and the screen approximation continuation operator in the viscous-acoustic medium are constructed and applied to the numerical simulation of the scattered wave field. The research results of the concave model and complex model indicate that due to the influence of medium viscosity, the energy of the deep reflected waves is weaker in the forward modeling records of the thin slab approximation method and screen approximation method, and the dominant frequency of seismic waves moves towards the low-frequency direction; Compared with the finite difference results, they only calculate one reflection, and there are no multiple wave signals in the seismic records. Finally, We discuss the thin slab approximation and the screen approximation method for detail around the division of the thickness of the thin slab, the selection of the reference frequency, and the non-uniformity of the medium.

Stability analysis of circular tunnels using spatiotemporal accelerations formulated considering heterogeneity of seismic wave propagation velocities

The space–time dependent horizontal and vertical seismic accelerations in a soil medium owing to the inhomogeneity in the shear and primary wave propagation velocities were analytically derived satisfying the boundary conditions on the ground surface and the base. The developed analytical formulations were applied to study the influence of wave velocity heterogeneity on the support pressure required for the circular tunnel stability placed in granular soils using the stress-based limit analysis in conjunction with finite elements. The support pressure was determined as the maximum normal stress exerted by the surrounding earth at its ultimate failure on the tunnel boundary. Further, the effect of frequency of seismic waves on the seismic accelerations, magnitude of tunnel support pressure and the variation of normal stress around the tunnel periphery has been presented in detail. The support pressure was found to be higher considering the heterogeneous wave velocity than the uniform one. A lower dimensionless frequency resulted in higher support pressures for a lower wave velocity ratio and higher power parameter of the power law used to model the wave velocity profile. Otherwise, for higher wave velocity ratio, the effect of power parameter diminishes, and the support pressure is higher for higher dimensionless frequency.

Preliminary design and evaluation method for the seismic isolation layer of a shield tunnel

Theoretical analyses and numerical simulations, proposed to increase the efficiency of tunnel seismic isolation measures, are too complex for solving practical problems. Herein, a simplified design method for a tunnel isolation layer is developed for preliminary calculations of the required physical parameters based on the surrounding rock conditions and seismic isolation performance. The internal force response of a shield tunnel in homogeneous ground before and after the installation of a seismic isolation layer is determined using the proposed method, considering the coupled effect of the isolation layer and surrounding rock by calculating the equivalent elastic modulus. The effectiveness of the derived method is verified using wave function expansion and finite element numerical simulation methods. The results obtained using the simplified design formulae are consistent with those obtained using the wave function expansion method. Furthermore, the effects of the seismic wave frequency, surrounding rock type, elastic modulus, and thickness of the seismic isolation layer on the seismic isolation effect are examined via parametric analysis. The proposed method could be applied to preliminary design and evaluation of seismic isolation layers for shield tunnels with different surrounding rock types.

A benchmark study for quasi-static numerical upscaling of seismic wave attenuation and dispersion in fractured poroelastic rocks

Numerical simulation is an effective tool for comprehending fluid flow behavior and solid skeleton deformation within porous media, as well as obtaining valid seismic information. The elastic response of seismic waves, serving as an intermediary linking material properties and seismic attributes, is influenced by a combination of the wave-induced fluid flow (WIFF) effects and stress interactions. However, the impact of stress interactions is frequently overlooked in numerous studies, primarily due to the complex distribution of subsurface fractures makes it difficult to clarify the effects caused by local stress perturbations. Therefore, we present a numerical upscaling procedure as a benchmark process to quantify seismic wave attenuation and dispersion in fractured porous media simulations. The procedure is based on COMSOL Multiphysics and allows for the simulation of the energy dissipation resulting from the compression of a model with arbitrary forms of fluid saturation, geometry, and petrophysical parameters by seismic waves. We analyze the fracture models with different spatial distributions and infills to understand the mechanism. Our simulation results show the efficient and accurate capabilities of the numerical upscaling procedure in simulating the acoustic properties of fractured porous media and demonstrate the physical processes at various frequencies. In addition, our study yielded corresponding results: 1) the diverse spatial distribution of fractures not only gives rise to peak anomalies but also influences both the attenuation peaks and characteristic frequencies of seismic waves, thus reflecting the attenuation phenomena occurring at different scales; 2) various infills exhibit distinct sensitivities to fracture morphology and stress interactions.

Numerical Analysis of the Dynamic Response Law of Counter-Tilt Layered Rock Slopes

Counter-tilt layered rock slopes are common types of slopes that are susceptible to destabilizing damage under seismic action. Therefore, the dynamic response law of counter-tilt layered rock slopes under seismic action is of great significance for the study of slope stability. This study utilizes UDEC (Universal Distinct Element Code) numerical simulation software to vary slope geometry and seismic wave parameters, such as joint thickness, joint inclination angle, slope angle, seismic wave frequency, amplitude, and duration. The maximum displacements of the monitoring points of a slope were obtained, and the dynamic response law of counter-tilt layered rock slopes under seismic action was investigated. The results yielded the following insights: (1) The thickness of the joints of a slope is an important factor affecting the dynamic response of a slope, and with the increase in the thickness of the joints, the maximum displacement of each monitoring point of the slope will decrease. (2) The maximum displacement of a slope increases with the increase in the joint inclination angle and the slope angle. When the joint inclination angle is less than 50°, the change in the joint inclination angle has less of an effect on the maximum displacement of the slope in the x and y directions. When the joint inclination angle is more than 50°, the maximum displacement of the slope in the x and y directions increases faster with the change in the joint inclination angle, and a similar pattern is observed for the slope angle. (3) Slopes are less susceptible to damage when both the joint inclination angle and the slope angle are less than 50°, and the probability of slope damage increases significantly when both are greater than 50°. (4) The maximum displacement at each monitoring point of a slope increases with the frequency, amplitude, and duration of a seismic wave. (5) Seismic wave amplitude has the greatest effect on the dynamic response of a slope, followed by duration, and frequency has the weakest effect on the dynamic response of a slope. The conclusions drawn in this paper can be useful for the control of counter-tilt layered rock slopes.

Development of a new base isolation system using the concept of metamaterials

Metamaterials are making a breakthrough in seismic wave manipulation with their ability to yield wave filtration properties that cannot be realized inherently through conventional construction materials. The popularly used seismic vibrational control techniques, such as base isolation, fall short at low-frequency regions of the spectrum and fail to encompass both flexible and rigid structures. Using the concept of metamaterials, the phenomena of local resonance and Bragg scattering can create a stop band region of frequencies that undergo vibrational wave filtration. This study proposes a two-dimensional periodic foundation system with steel-silicone embedded assemblies to serve as local resonators. The proposed foundation can cover a wide and ultra-low frequency region in its band gap, enveloping the principal frequencies of seismic waves (i.e., 0.2 Hz to 10 Hz). This two-dimensional periodic foundation can also exhibit a Bragg region without local resonators but is made more efficient with the help of steel-silicone resonators (SSR). Upon experimental testing, the scaled-down prototype of the proposed foundation with three locally resonant panels embedded with SSR showed an average of 50 % attenuation of displacement within the frequency band gap (i.e., 2.54 Hz to 8.08 Hz). Moreover, the experimentation showed a 73 % attenuation at the resonant frequency of SSR. Experimental testing affirmed the frequency band gap obtained through mathematical formulation. Furthermore, the theoretical results demonstrate that the full-scale proposed periodic foundation would be able to achieve a band gap that covers frequencies from as low as 0.3 Hz to 7.35 Hz. This study is the first attempt to set the baseline for periodic foundations capable of fully mitigating the entire spectrum of seismic vibrational effects on structures.

Application of Forward Modeling in Putaohua Oilfield

Putaohua Oilfield is bounded by the large fault on the south side of Pu A1 Well. It is divided into Pubei and Punan development zones on the plane. It is an oilfield that has been developed by water injection for more than 30 years. With the increase of development time, the water content of oil wells increases rapidly, and the oil production of the oilfield decreases rapidly,In order to realize the study of petroleum geological potential in this area, find out the favorable target area for well layout, and effectively improve the drilling success rate,first of all, we need to do forward modeling for the study area to lay a solid foundation for subsequent research. This paper analyzes the change characteristics of seismic wave frequency attenuation attribute in reservoir oil and gas, and applies it to the study of reservoir oil and gas prediction in Putaohua Oilfield.

Changes of Hydraulic Transmissivity Orientation Induced by Tele‐Seismic Waves

AbstractWater level monitoring data from 5 deep wells on the North China Platform are used to study how two large earthquakes impact deep aquifers. After the passage of seismic waves from earthquakes, a subset of these wells shows changes in the phase shifts of water level responses to lunar diurnal (O1) and semidiurnal (M2) tides. We fit a model for the tidal responses of hydraulically conductive fractures that intersect the wells to explain the phase and amplitude of responses to both O1 and M2 tides. To explain changes after the earthquakes with this model, the apparent orientation of fractures must change. Because the stresses are small, we propose that changes in tidal response occur when the passage of seismic waves modifies the hydraulic connectivity of a network of fractures by unclogging or clogging flow paths, thus changing the apparent orientation of the fractures controlling tidal responses. The seismic energy density that results in changes appears to decrease as the dominant frequency of seismic waves increases.

Study on the Influence of Seismic Wave Parameters on the Dynamic Response of Anti-Dip Bedding Rock Slopes under Three-Dimensional Conditions

As a result of earthquakes, the deformation and failure caused by anti-dip bedding rock slopes are large, and their seismic dynamic response law is complex. Using the three-dimensional discrete element numerical analysis software 3DEC, the influence of seismic wave parameters on the dynamic response of anti-dip bedding rock slopes was systematically studied, with special focus on the influence of the angle between seismic wave incidence direction and slope trend on the dynamic response of anti-dip bedding rock slopes under three-dimensional conditions. The orthogonal test was designed to conduct sensitivity analysis of five seismic parameters, including seismic wave amplitude, incidence angle of the S-wave, frequency, duration, and the time difference between the P-wave’s and the S-wave’s peak. The results revealed that the S-wave’s amplitude As and the holding time T of the seismic wave are positively correlated with the acceleration amplification factor of the slope, and the incident direction γ of the S-wave is negatively correlated with the acceleration amplification factor of the slope. The increase of seismic wave frequency f and the time difference Δt between the P-wave’s and the S-wave’s peak lead to the first increase and then decrease of the Y-directional displacement of the slope. The sensitivity of each seismic wave parameter to the Y-directional acceleration amplification factor at the shoulder of anti-dip bedding rock slopes in earthquake conditions is ordered as follows: S-wave’s amplitude As > frequency f > S-wave’s incidence angle γ > the time difference Δt > holding time T. the study results provide reference and basis for stability evaluation and engineering design of anti-dip bedding rock slopes in areas with high seismic intensity.

Interpretation method of tight sandstone based on seismic forward modeling: a case study of Permian in Southeast Ordos Basin

Based on Permian data and the reflection coefficient convolved 0° and 90° phase ricker wavelets form different phases of synthetic seismic sections. This paper theoretically discusses three aspects: one is Permian sandstone thickness and seismic amplitude, the second is tight sandstone (tuning) thickness and seismic wave frequency, and the last is tight sandstone and seismic wave phase. The result shows that when sandstone thickness is greater than seismic wavelength λ/4, the sandstone thickness can be determined through the time difference between the sandstone’s top and bottom Peaks and troughs. When sandstone thickness is less than λ/4, only the seismic reflection amplitude of the top surface of sandstone was used to determine the thickness of sandstone. In the 0° phase seismic model, peaks were located on the thin layer’s upper part and trough in the lower half, with no correspondence between the polar and lithology. In the 90° phase synthesis record, the thin sandstone layer roughly corresponds to the seismic reflection trough. 0° and 90° phase synthesis have the exact vertical resolution; the frequency variation can reflect sand body distribution. The optimal frequency makes the thickest layer of sandstone reach amplitude-frequency tuning (tuning frequency).

Mechanical degradation mechanism of rock under seismic disturbance stress

During the action of periodic seismic disturbance stress, the rock mass surrounding buried structures will show fatigue damage owing to cyclic loading. To explore the fatigue characteristics and mechanical degradation mechanism of this process, fatigue loading and uniaxial compression tests were carried out on gypsum samples. The conclusions are as follows. With increasing seismic wave amplitude, the stress loading and unloading velocity gradually increases, and the opening of the stress–strain hysteresis loop gradually increases. With increasing seismic wave frequency, the dip angle of hysteresis loops gradually inclines to the σ -axis (where σ is stress), and the variation amplitude of hysteresis loops on the ε -axis (where ε is strain) decreases gradually. This shows that the greater the amplitude of the seismic wave and the lower the frequency, the greater the damage to rock. Under seismic wave disturbance, with increasing number of disturbances, the original cracks in the sample gradually spread and infiltrate the rock, and secondary cracks gradually develop, indicating that the physical and mechanical properties of the rock gradually deteriorate. There is a strong correlation between the acoustic emission of samples and the stages of the stress–time curve for uniaxial compression. According to the acoustic emission characteristics, the stress–time curve can be divided into four stages: the initial loading stage, the stable crack growth stage, the unstable crack growth to failure stage and the post-peak stage. Compared with the sample before fatigue, the peak strain decreases significantly and the impact energy index increases significantly after fatigue loading. This indicates that some original cracks in the sample are compressed under seismic disturbance, the brittleness of the sample is enhanced and the rockburst tendency is greatly enhanced.

Velocity Dispersion Attribute in Carbonate Reservoir

Detection of the presence of saturated hydrocarbons in pores or rock fractures is a major problem in the field of exploration geophysics which is interesting to study. Some of the fluid saturation indicators were originally derived from the Zoepprit equation. However, the indicator that is derived from the linearization of the reflection coefficient is not influenced by frequency. In fact, frequency is a physical quantity that is very sensitive to the presence of fluid in a pore or rock fracture. Seismic waves will experience attenuation and dispersion when propagating through a porous medium or gas-saturated fractures. Therefore, we need an indicator whose value is influenced by changes in the frequency of seismic waves. This indicator is an attribute of the velocity dispersion. In previous studies, the velocity dispersion attribute was used to detect the fluid content of gas in sandstone. Based on this research, it turns out that it shows effective results in mapping the presence of saturated gas zones in the carbonate pores. In the end, the results of this study will be able to map the presence of saturated gas zones in carbonate reservoir.

Importance of seismic wave frequency in FEM-based dynamic stress and displacement calculations of the earth slope

Abstract Reliable assessment of earthen dams’ stability and tailing storage facilities widely used in the mining industry is challenging, particularly under seismic load conditions. In this paper, we propose to take into account the effect of the dominant frequency of seismic load on the stability assessment of tailing/earthen dams. The calculations are performed by finite element modelling (FEM) with the Mohr–Coulomb failure criteria. To separate the frequency content from other dynamic parameters describing the seismic wave, synthetic waveforms with identical amplitude and attenuation characteristics, but differing spectral characteristics have been used. The analysis has been performed for three different slope angles and two scenarios of seismic wave propagation. Consequently, the changes of total displacement and shear stresses depending on the frequencies have been determined and clearly show that lower frequencies cause higher stress levels and displacement. Finally, the response surface methodology has been applied to determine how different parameters affect the slope stability under dynamic load conditions. Overall, this study is a first step to improve the existing methods to assess slope stability when considering seismic load.

Co-seismic deformation of the 2017 Mw 6.6 Bodrum–Kos earthquake in speleothems of Korakia Cave (Pserimos, Dodecanese, Greece)

Structural mapping and dating of damaged speleothems have been used to investigate earthquake records in caves, especially of large infrequent events. However, there are few reports of damages in caves visited before and after a particular earthquake, where the damage can be directly related to a recorded event. We mapped the previously unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece) prior to the 2017 Mw 6.6 Bodrum–Kos earthquake. The Dodecanese is at the transition between the Aegean and Anatolian region and is known for its strong seismicity. Although several hundred stalactites with large height-to-width ratios are preserved on the roof of Korakia Cave, the cave has an extensive record of damaged speleothems, which have been caused by movements along normal faults. Here we present new data and 230Th/U-ages of paleoseismic events that are partly older than the limit of the dating method. A cave visit after the 2017 Mw 6.6 Bodrum–Kos earthquake revealed that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, had been chipped off by movements along the fractures during that earthquake. We conclude that movements along fractures or faults during seismic events can easily damage stalagmites and stalactites. However, damage related to the resonance frequency of the dripstones matching with the seismic wave frequency, which has been suggested to break dripstones with large height-to-width ratios, was not observed in Korakia Cave.

ГЕОЛОГІЧНА ПРИРОДА СЕЙСМІЧНИХ ВІДОБРАЖЕНЬ В ОСАДОВОМУ ЧОХЛІ СХІДНОЇ ЧАСТИНИ АБШЕРОН-ПРИБАЛХАНСЬКОГО ПОРОГУ

The Absheron-Prebalkhan tectonic zone, often called as the Absheron-Prebalkhan ridge, is a link between two large oil and gas basins of the world, which differ in the genetic level of the basement, i.e.: the South Caspian (SCB) and the Middle Caspian basins (MCB). The considered area has been completely covered by detailed seismic and gravity surveys over the past decades. The article presents material illustrating the information content of seismic sections in different parts of the region, which are characterized by different seismogeological conditions. As a result of the analysis of the latter, the author specified and determined four seismic horizons: SH-A (Akchagyl), SH-I (tops of RS), SH-II (horizon VIII) and SH-III (lower RS) based on the dynamic expressiveness, length, and resolution of the record. The tracking quality of these horizons is not the same. The identification of seismic intervals, which correspond to structural levels based on objectively determined seismic parameters, such as the configuration and relative position of reflections, their continuity, as well as the amplitude and frequency of seismic waves were the basis for seismic stratigraphic analysis of the wave field. The compiled schematic structural maps show the geological structure of the red-colored strata and Akchagyl deposits and the correlation of the structural plans of the latter clearly. Comparison of complex geological and geophysical materials allows to determine the character of the distribution of lithofacies features of RS deposits.

Application of Spatio-Temporal Spectral Analysis for Detection of Seismic Waves in Gravitational-Wave Interferometer

Mixed spatio–temporal spectral analysis was applied for the detection of seismic waves passing through the west–end building of the Virgo interferometer. The method enables detection of a passing wave, including its frequency, length, direction, and amplitude. A thorough analysis aimed at improving sensitivity of the Virgo detector was made for the data gathered by 38 seismic sensors, in the two–week measurement period, from 24 January to 6 February 2018, and for frequency range 5–20 Hz. Two dominant seismic–wave frequencies were found: 5.5 Hz and 17.1 Hz. The presented method can be applied for a better understanding of the interferometer seismic environment, and by identifying noise sources, help the noise–hunting and mitigation work that eventually leads to interferometer noise suppression.