Different Types Of Seismic Waves Research Articles

Pseudo-Helmholtz decomposition for an elastic VTI wavefield based on wavefront phase direction

P and S waves are coupled when propagating in anisotropic elastic media. The separation of P and S waves helps to study the characteristics of different types of seismic waves as well as mitigating crosstalk artifacts in elastic reverse time migration and elastic full-waveform inversion. At present, the methods of seismic wave mode separation in anisotropic media are mainly built on divergence- and curl-like operations, pseudo-Helmholtz decomposition, and low-rank approximation. We develop a new pseudo-Helmholtz decomposition operator based on eigenform analysis and the wavefront phase direction to decompose vertically transversely isotropic elastic wavefields. The corresponding P-/S-wave decoupling formulas are also derived in detail. Compared with the divergence- and curl-like methods, the new method does not change the phase of P and S waves. Compared with existing pseudo-Helmholtz decomposition methods based on eigenform analysis, our method achieves more accurate wavefield separation than the zero-order pseudo-Helmholtz decomposition operator. Our method requires solving one vector Poisson equation only, resulting in much less computational cost than the existing first-order pseudo-Helmholtz decomposition methods. In addition, the accuracy of our method is analyzed by providing homogeneous media with different parameter settings. Finally, the numerical examples demonstrate that the new pseudo-Helmholtz decomposition method is effective, efficient, and robust against random noise.

Study on Seismic Response of Aqueduct under Different Types of Seismic Waves

Study on Seismic Response of Aqueduct under Different Types of Seismic Waves

Shaking Table Test for Seismic Isolation Performance of Adjustable Height Seismic Isolation Rubber Bearing

To study the seismic isolation effect of adjustable height seismic isolation rubber bearing, a continuous girder bridge was subjected to a shaking table test study with full bridge scaling to compare the seismic isolation effects of plate rubber bearings, natural rubber bearings (LNR) and adjustable height seismic isolation rubber bearings under different types of seismic waves, loading directions and seismic intensities.The test results show that when the seismic intensity is small, the seismic isolation performance of the three types of bearings is relatively close. But when the seismic intensity is large, the seismic isolation effect of the adjustable height isolation bearing is better than that of the plate rubber bearing and LNR bearing. Adjustable height isolation rubber bearing can significantly reduce the acceleration of the bridge deck plate, shear force and bending moment in the bottom of piers.

Shaking table experimental investigations on dynamic characteristics of CFRP cable dome

Carbon fiber reinforced polymer (CFRP) bars have the feature of lower density, higher strength and better anti-fatigue performance compared with steel bars. Therefore, CFRP is a kind of ideal material for a long-span spatial structure. To explore the dynamic performance of spatial structures and take full advantages of CFRP bars in long span cable dome structures, a CFRP cable dome scale model with a diameter of 5.4 m was designed for a shaking table test. In this model, struts and cables were made of CFRP material except that the internal ring beams were fabricated with steel. In the test, new types of joint forms and anchoring configurations for CFRP cable dome structures were proposed because the existing forms for steel domes cannot be applied to CFRP dome structures. In addition, three kinds of seismic waves including Elcentro wave, Kobe wave and Pasadena wave were selected to generate 12 load cases and the maximum acceleration was 900 Gal. The acceleration and strain response of the model under different types of seismic waves was researched. It is demonstrated that middle-ring upper joints have the largest acceleration response because the control vibration modes of the CFRP cable dome structure are anti-symmetric mode. In addition, a CFRP dome numerical model was established to carry out modal analysis by program ANSYS. By comparing the results of finite element modal analysis with the measured frequencies, the natural vibration modes of the structure are analyzed. Based on the results of seismic wave spectrum analysis and structural modal analysis, the Pasadena wave, which has a wide low frequency region for high Fourier amplitude, can excite the greatest acceleration response.

Study on the shock-absorbing effect of a new staggered story isolated structure under the long-period earthquake motion

The finite element model of a new staggered story isolated structure is established. Using the time-history analysis method, the dynamic response state of the structure at each time step is calculated by integrating the acceleration time-history data step-by-step. Three different types of seismic waves (ordinary seismic wave, near-fault impulse seismic wave, far-field quasi harmonic and long-period seismic wave) are input respectively for dynamic time history analysis. The result indicates that the new staggered story isolated structure has a good shock absorption effect under the action of three different types of seismic waves. There are certain differences in the shock absorption effect under the three kinds of ground motions. The seismic response under ordinary ground motions is minimal, but the seismic response of the structure increases in response to far-field quasi harmonic and long-period ground motions and the near-field fault pulse ground motions. Meanwhile, the inter-story shear force, inter story acceleration, inter-story displacement, damage, and the energy input are all increasing, However, compared with the aseismic structure, the inter-story shear force is reduced by 48%, the inter-story acceleration is reduced by 23%, the inter-story displacement is reduced by 48%, and the energy dissipation rate of the isolated layer is 65%. In addition, the isolated bearing is in good condition during occasional earthquakes under normal ground motion. However, the bearing exceeds the permissible range during near-fault impulse ground motion and far-field harmonic and long-period earthquakes. Therefore, special consideration should be given to the area where the far-field harmonic and long-period ground motion are involved.

Joint passive seismic imaging based on surface wave inversion and reflection wavefield retrieval: A case study in the sedimentary basin areas adjacent to Well Songke-2

Owing to their cost-effectiveness, environmental friendliness, and high-efficiency, passive seismic methods are widely used in geophysical exploration. However, field passive seismic data suffer from low signal-to-noise ratio, as well as the fact that different types of seismic waves are naturally mixed together, which can affect the accuracy of subsurface imaging results and the subsequent geological interpretation. In this paper, we demonstrate that these problems can be addressed and present a case study on passive seismic detection in sedimentary basin areas adjacent to Well Songke-2 in Songliao Basin. To obtain accurate and reliable imaging results of the sedimentary strata, a detailed practical scheme is proposed, where fundamental and higher mode surface wave dispersion curves are inverted for obtaining the near-surface S-wave velocity profile, and the body wave component of ambient noise is utilized to retrieve the reflection wavefield information. The obtained profiles from surface wave inversion and reflection wavefield retrieval illustrate similar underground structures. The marker boundaries T2 (1.5 s) and T4 (2.1 s) are well demonstrated, and a low velocity stratum (0.4 s) is detected at a shallow depth of around 400–600 m. Further, the results are highly consistent with the data obtained from borehole logging of Well Songke-2 and the deep reflection seismic profile adjacent to this area, which indicates that the surface wave and body wave in passive seismic data can be utilized together to contribute to a detailed and accurate subsurface imaging and interpretation. Overall, this study investigated and validated the reliability and accuracy of the combination use of passive seismic methods for geological structure exploration, which can further boost their applications for geological interpretation in sedimentary basin areas.

A comparative analysis of seismic response of shallow buried underground structure under incident P, SV and Rayleigh waves

In this study, A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P, SV and Rayleigh waves are established, based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input. After verifying the calculation accuracy, a comparative study on seismic response of a shallow-buried, double-deck, double-span subway station structure under incident P, SV and Rayleigh waves is conducted. The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves. The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves. At the bottom of the side wall, the top and bottom of the center pillar of the underground structure, the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close, and are significantly larger than the calculation result under the incidence of P wave. At the center of the side wall and the top floor of the structure, the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave. In addition, the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions, and the magnification effect in the vertical direction is more significant. Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves, sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.

A Threshold Model of Tailings Sand Liquefaction Based on PSO-SVM

The liquefaction of tailings sand caused by seismic loads is a major problem in ensuring the safety of tailings ponds. Liquefaction may cause uncontrolled fluidized failure of the dam body, causing considerable damage to the lives, property and environment of people downstream. In this paper, a prototype tailings sand is used as the material to consider the main factors affecting liquefaction (i.e., dynamic load, soil quality, burial and static conditions). By embedding acceleration, pore pressure and earth pressure sensors in the rigid design of the self-designed rigid model box, different types of seismic waves of different ground motion amplitudes (PGA) were induced in a shaking table test of tailings sand liquefaction. The seismic intensity, waveform (class II, III and IV seismic waves) and active earth pressure of the PGA characterizing dynamic factors were obtained, and the static factors were characterized. The dynamic shear stress ratio, the peak acceleration of the earthquake, the pore pressure of the drainage factor and the buried depth (overlying effective pressure) characterize the soil conditions. SPSS software was used to analyze the factor dimension reduction, and the most suitable factors for factor analysis were obtained. Particle Swarm Optimization (PSO) was used to optimize the parameters, and the improved PSO-SVM algorithm was compared with the existing genetic algorithm (GA) and grid node search (GS). The algorithm used in this paper is fast and has a relatively high accuracy rate of 92.7%. The established threshold model method is of great significance to predict the liquefaction of tailings sand soil under the action of ground motions and to carry out safety managemenin advance, which can provide a certain reference for the project.

Seismic analysis of a transition tunnel constructed with TBM and mining method

A transition tunnel is generally built to connect a TBM tunnel and a mining tunnel, given the different cross sections associated with each construction method. The transition tunnel may be sensitive to earthquake damage since the tunnel cross-section and stiffness change along the tunnel axis. Studying the seismic performance of the transition tunnel structure, a subtle 3D finite element model is carried out. Comparing with the calculation results of SHAKE91, a reasonable non-reflective boundary condition is used. The concrete adopts an elastoplastic damage constitutive model, and the surrounding rock mass uses an elastoplastic constitutive model based on the Drucker-Prager yield criterion. The effects of different ground motion magnitudes and different types of seismic waves are calculated and analyzed through dynamic time-history method. The calculation results show that the impact range of the construction method butted composite lining section on the tunnel structure of the mine tunnel and the TBM tunnel is about 10m, and the reinforcement of the inner lining will cause a sudden change in the stress of the outside TBM tunnel structure. Moreover, the compressive stress of the surrounding rock and tunnel structure is small, and the structural damage mainly occurs in the area of the arch shoulder and arch foot.

Vertical wave barriers for vibration reduction

Earthquakes generate a series of waves that penetrate the Earth. Depending on proximity to the epicenter of an earthquake, different types of seismic waves dominate at the surface of the Earth. Distinct kinds of seismic waves shake the ground in various ways. Love and Rayleigh waves both produce ground shaking at the surface of the Earth, which exponentially attenuates with depth. Surface waves can often constitute the most important component of ground shaking far from the epicenter due to the fact that the decrease in their amplitude diminishes less rapidly with distance; thus, these waves can be dangerous and destructive. Hereinafter, the concept of a seismic barrier in soil protecting the area from seismic waves of the Rayleigh type is considered. The main idea behind this type of protection is to prevent seismic waves from transmitting wave energy into the protected zone, decreasing the amplitudes of displacements, velocities and accelerations at the points behind the barrier. In this article, numerical simulations on planar and spatial models are presented and discussed for the cases of horizontal and vertical barriers using different mechanical and geometrical parameters of the barriers. Additionally, an algorithm for a multi-parametric optimization of the barrier geometry and material is presented and adopted for specific soil conditions.

Research on hydraulic servo control system for field test of ground motion parameters

The hydraulic servo control system of the ground motion parameter field test system is introduced in this paper. The hydraulic servo control system mainly includes the seismic wave generating equipment system and the servo control system. And the equipment system consists of the P-wave and the S-wave generator. The main advantage of the hydraulic servo control system is that P-wave and S-wave generator can generate both p-wave and S-wave. The seismic waves produced are characterized by strong stability and high energy, which can overcome the shortcomings of instability, less energy and poor repeatability of the on-site wave generating device. It is necessary to generate the waveform of different types of seismic waves, such as sine wave, cosine wave, square wave and random wave. The vibration frequency of the seismic wave can be controlled to meet the actual demand of the seismic wave in engineering. The hydraulic servo control system can be run stably for a long time, without interference and unreliable operation in various environments and states, which can be of great significance for the seismic safety evaluation of the engineering site.

Possible mechanisms of co-seismic electromagnetic effect

We analyze theoretically two possible sources of co-seismic electromagnetic response to the propagation of various types of seismic waves caused either by the electrokinetic phenomena or geomagnetic inductive effect. The differences between these two generation mechanisms have been examined for different types of seismic waves (P, S, and Rayleigh-Love). Theoretical relationships describing the dependence of the co-seismic signal amplitude, polarization and apparent impedance on the earthquake seismic moment and magnitude have been derived as a function of distance. We indicate an observational possibility to discriminate seismo-electrokinetic and seismo-magnetic effects and to estimate their contribution into a recorded co-seismic electromagnetic signal. Magnitudes and polarization of these signals are shown to depend strongly on the type of seismic wave and local crust parameters, such as streaming potential coupling coefficient, conductivity, inhomogeneity, etc. Co-seismic electromagnetic signals, though not directly applied for earthquake prediction, contain a useful information on local crustal phenomena, and can be used to identify “sensitive” zones perspective for the monitoring of precursory electromagnetic disturbances.

Numerical simulation of earthquakes impact on facilities by grid-characteristic method

Numerical modeling of dynamic wave processes in heterogeneous media allows to investigate the earthquake stability of different constructions. The aim of this work is to study the earthquakes’ impact on the ground buildings and underground facilities. The use of grid-characteristic method makes possible to take into account the physics of arising wave processes. The use of systems of hierarchical grids allows to perform a calculation of seismic waves directly from the earthquake source to the ground buildings and underground facilities. The arising area of cracks in this ground building (two-storied houses) at different times from different types of seismic waves is studied. Also the impact of earthquake on the underground facilities is considered. The dynamical arising of cracks and destruction into the underground facilities made from different types of reinforced concrete due to the impact of different types of seismic waves is investigated in this paper. The results demonstrate a possibility of investigation earthquake stability of underground facilities and living buildings using modeling of seismic waves’ propagation directly from the earthquake centers.

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.

Nonlinear attenuation from the interaction between different types of seismic waves and interaction of seismic waves with shallow ambient tectonic stress

AbstractStrong seismic waves bring rock into frictional failure at the uppermost few hundred meters. Numerous small fractures slip with the cumulative effect of anelastic strain and nonlinear attenuation; these fractures should not distinguish between remote sources of stress. Still, frictional failure criteria are not evident especially when seismic waves change the normal traction on fractures. We identify three earthquakes as examples where consideration of interaction among dynamic stresses from different wave types and ambient tectonic stress provides theoretical predictions of nonlinear attenuation that are potentially testable with single station seismograms. For example, because Rayleigh waves produce shallow horizontal dynamic tension and compression, frictional failure should preferentially occur on the tensile half‐cycle if no shallow tectonic stress is present and on the compressional half‐cycle if the tectonic stress is already near thrust‐faulting failure. We observed neither effect on records from the 2011 Mw 9.0 Great Tohoku earthquake. However, Rayleigh waves from this event appear to have brought rock beneath MYGH05 station into frictional failure at ∼10 m depth and thus suppressed high‐frequency S waves. The tensile half‐cycle of high‐frequency P waves reduced normal traction on horizontal planes beneath station IWTH25 during the 2008 Mw 6.9 Iwate‐Miyagi earthquake, weakening the rock in shear and suppressing high‐frequency S waves. The near‐field velocity pulse from the 1992 Mw 7.3 Landers earthquake brought the uppermost few hundred meters of granite beneath Lucerne station into frictional failure, suppressing high‐frequency S waves. These moderately positive examples support the reality of nonlinear wave interaction, warranting study future strong ground motions.

A digital seismogram archive of nuclear explosion signals, recorded at the Borovoye Geophysical Observatory, Kazakhstan, from 1966 to 1996

Seismologists from Kazakhstan, Russia, and the United States have rescued the Soviet-era archive of nuclear explosion seismograms recorded at Borovoye in northern Kazakhstan during the period 1966–1996. The signals had been stored on about 8000 magnetic tapes, which were held at the recording observatory. After hundreds of man-years of work, these digital waveforms together with significant metadata are now available via the project URL, namely http://www.ldeo.columbia.edu/res/pi/Monitoring/Data/ as a modern open database, of use to diverse communities.Three different sets of recording systems were operated at Borovoye, each using several different seismometers and different gain levels. For some explosions, more than twenty different channels of data are available. A first data release, in 2001, contained numerous glitches and lacked many instrument responses, but could still be used for measuring accurate arrival times and for comparison of the strengths of different types of seismic waves. The project URL also links to our second major data release, for nuclear explosions in Eurasia recorded in Borovoye, in which the data have been deglitched, all instrument responses have been included, and recording systems are described in detail.This second dataset consists of more than 3700 waveforms (digital seismograms) from almost 500 nuclear explosions in Eurasia, many of them recorded at regional distances. It is important as a training set for the development and evaluation of seismological methods of discriminating between earthquakes and underground explosions, and can be used for assessment of three-dimensional models of the Earth’s interior structure.

The Influence of Pile-Pier Reinforcement Ratio on the Development of Plastic Zone of Bridge Structure

In this paper, using elastic-plastic fiber unit model for a continuous beam bridge structure and foundation to analyses the nonlinear seismic response of pier and pile foundation considering pile-soil interaction and the different types of seismic wave on the pile foundation and the pier dynamic response, focusing on the development of plastic zone and dynamic response of structure under different pile-pier reinforcement ration conditions. The results show that, with the pile pier reinforcement ratio increases, the response plasticity of pile and pier show a different trend; so pile-pier reinforcement ration is an important factor of dynamic characteristics for the bridge pier supported by group piles system; the pier reinforcement ratio not only impact on development of the plastic zone of the pier, but also impact on the pile. In addition, different types of seismic waves on the structure are different, the long-period seismic waves maximum, followed by inland direct seismic waves, plate boundary seismic wave minimum.

Dynamic response characteristics of super high-rise buildings subjected to long-period ground motions

Spectrum characteristics of different types of seismic waves and dynamic response characteristics of super high-rise building structures under long-period ground motions were comparatively analyzed. First, the ground response wave (named LS-R wave) of a soft soil site with deep deposit, taking long-period bedrock seismic record as input, was calculated by wave propagation method. After that, a TOMAKOMAI station long-period seismic record from the Tokachi-Oki earthquake and conventional El-Centro wave were also chosen. Spectrum characteristics of these waves were analyzed and compared. Then, a series of shaking table tests were performed on a 1:50 scale super high-rise structural model under these seismic waves. Furthermore, numerical simulation of the prototype structure under these excitations was conducted, and structure damages under different intensive ground motions were discussed. The results show that: 1) Spectrum characteristics of ground response wave are significantly influenced by soft soil site with deep deposit, and the predominant period has an increasing trend. 2) The maximum acceleration amplification factor of the structure under the TOM wave is two times that under the El-Centro wave; while the maximum displacement response of the structure under the TOM wave is 4.4 times that under the El-Centro wave. Long-period ground motions show greater influences on displacement responses than acceleration responses for super high-rise building structures. 3) Most inelastic damage occurs at the upper 1/3 part of the super high-rise building when subjected to long-period ground motions.

Study on Seismic Dynamic Response of Offshore Wind Turbine Tower with Monopile Foundation Based on M Method

Making sure the safety of wind turbine tower structure in service is particularly important with the development of offshore wind turbine facility. In order to make mechanical characteristics of structure explicit, dynamic responses of structure under three different types of seismic waves were analyzed by m method and considering monopile-soil-structure interaction, then comparison with the situation when structure was consolidated in the bottom was made. The result shows, dynamic response was most obvious under the action of far-field seismic wave in such high-rise structure as wind turbine tower. When the acceleration peak of far-field seismic wave was in the level of 8-degree rare earthquake, structure would be unsafe with an oversize displacement at the top of tower. Compared with structure consolidated in the bottom, dynamic response of structure was effected by the intensity and stiffness of soil around the pile. The interaction of soil and foundation was needed to be considered in the analysis of dynamic response.

Ionospheric disturbances (infrasound waves) over the Czech Republic excited by the 2011 Tohoku earthquake

A train of large amplitude infrasound wave packets was observed by multipoint Continuous Doppler sounding system in the ionosphere over the Czech Republic on 11 March 2011. It is shown that these infrasound wave packets originated from vertical motion of the ground surface that was caused by arrival of seismic waves generated by the strong Tohoku earthquake. The infrasound wave packets were observed in the ionosphere at heights of ∼210–220 km about 9 min after the detection of corresponding wave packets on the ground, which is consistent with the calculated time for vertically propagating infrasound waves. Absolute values of cross‐correlation coefficients between ionospheric and ground measurements are typically higher than 0.9 (for two wave packets ∼0.98). The individual wave packets recorded on the ground have different observed horizontal velocities and correspond to different types of seismic waves. A comparison of vertical velocities of ground motion with oscillation velocities of air particles in the ionosphere indicates that almost 1/10 of the infrasound energy flux excited at the ground reached the altitudes of ∼210–220 km for wave periods longer than ∼30 s. Estimates of sound attenuation are performed. It is also shown that it is necessary to consider the value of electron density gradient at the reflection height of the sounding radio wave, and air (plasma) compression owing to the infrasound wave to get reasonable estimates of oscillation velocities of air particles from Doppler shift frequencies.