Effects Of Seismic Wave Propagation Research Articles

Performance of parallel double pipelines under non-uniform seismic excitation

This paper investigates the structural safety of parallel double-buried pipelines under non-uniform seismic excitation considering the soil-pipeline interaction. A three-dimensional nonlinear numerical model has been established to study the effects of seismic wave propagation and ground motion intensity, as well as the pipeline internal pressure and spacing between the pipelines on their structural safety. The dynamic response of the parallel double buried pipelines was evaluated in terms of the acceleration amplification, settlement of ground surface, and strain, displacement, and elliptical deformation of the pipeline. The results demonstrate that the seismic response of buried pipelines under non-uniform excitation has obvious nonlinear characteristics, especially when the loading intensity is high. It is found that the internal pressure has virtually no effect on the site acceleration response, but it amplifies the settlement of the ground surface. Meawhile, it inhibits the elliptic deformation of the pipeline. Furthermore, the variation of the elliptic deformation of parallel buried pipelines is found to be the same for different pipeline spacings considered in this study. On the other hand, the pipelines spacing has a significant influence on their seismic response as the interaction between the two pipelines gradually decreases with the increase in the spacing.

Research on the forward-modeling method of viscoelastic Chapman extension in partially saturated rocks

The propagation of seismic waves in fractured rocks is greatly influenced by the fracture system and fluid content. Seismic anisotropy varies with frequency and fluid saturation. Previous theories on frequency-dependent anisotropy (FDA) are mostly limited to the assumption of single-phase fluid, whereas almost all reservoirs are usually partially or fully saturated with one or more fluids. The inelasticity, heterogeneity, and anisotropy exhibited by real earth media seriously challenge the traditional theory of uniform fully elastic media. Therefore, based on the Chapman elastic theory, we consider the viscoelastic model, the relative mobility of saturated fluids, and the coupled effects of commonly independently considered squirt flow and patch effects on the frequency-dependent anisotropic seismic wave propagation in viscoelastic media. By calculating the frequency-dependent anisotropic elastic coefficients of two-phase immiscible fluid-saturated fractured rocks, a new viscoelastic Chapman extension model for FDA in partially saturated rocks, which includes the unified seismic wave propagation effects of squirt flow and patch effects, is constructed. The effect of relative permeability is significant, and compared to the case of complete saturation, the effective fluid mobility in partially saturated rocks may be lower, which may lead to nonmonotonic changes in elastic modulus and water saturation. Numerical experiments are conducted on our viscoelastic Chapman extension model to discuss the coupling effects of squirt flow and patch effects on the FDA of viscoelastic media in cracked rocks with partially saturated reservoirs, under the conditions of no fractures and the existence of fractures. The simulation results of the P-wave modulus, P-wave velocity, and anisotropy parameters confirm the validity of our method and model. We link the anisotropy of viscoelastic media with fluid flow parameters in fractures, which is conducive to improving the understanding of frequency-dependent seismic anisotropy in partially saturated rocks with fractures and the combination of seismology and reservoir engineering.

Seismic wave propagation analysis in the framework of generalized continuum mechanics theory

For the problems of seismic wave propagation, scale effects will appear while considering the microstructures of medium. Scale effects mean that new components of wave fields appear in the seismograms due to the microstructure interactions in the medium and vary with the change of the characteristic length scale parameters. The generalized continuum mechanics (GCM) theory which introduces the intrinsic length scales of the microstructures is suitable for analyzing the scale effects of seismic wave propagation. We adopt the concept of multi-scale microstructure interactions, that is, the modified couple stress theory, and the one-parameter second strain gradient theory, as two branches of the GCM theory, have the same definition characteristic length scale parameters of medium, to describe the microstructure interactions at different scales. Through the quantitative relationship between the characteristic length scale parameters of the medium and the micropore, the layered model of the characteristic length scale parameters of the micropore is constructed for numerical modeling in a unified framework, and the scale effects of seismic wave propagation is analyzed. More specifically, the asymmetric elastic wave equations under a unified framework are derived, and the physical definition of the characteristic length scale parameters of medium is given. And the influence of the characteristic length scale parameter of the micropore on the seismic wave propagation is focused on. Finally, the scale effects of seismic waves excited by high-speed trains under the viaduct system are analyzed, and some conclusions are drawn.

The generation of uniform hazard Floor Response Spectra

In the generation of Floor Response Spectra (FRS), there are significant uncertainties in the earthquake excitations and site conditions, which lead to uncertainty in the resultant FRS. A fully probabilistic method is developed to account for the uncertainties and to generate FRS with a desired return period (RP). The uncertainties in seismic inputs and geotechnical models from nuclear industry are considered in this research. A set of seismic inputs at the bedrock with different loading levels are used to represent the uncertainty in earthquake excitations. A large number of site profiles are developed by Monte Carlo simulation to account for the uncertainty in soil properties. Following site response analysis and soil-structure interaction (SSI) analysis, amplification factors are determined for each site under the excitations of different ground motions to address the effects of seismic wave propagation and SSI. The uncertainties are propagated from site response analysis to SSI analysis consistently. Based on these analyses and seismic hazard curves at the bedrock, uniform hazard FRS are obtained with a complete probabilistic description. In the numerical examples based on the uncertainty model in nuclear industry, the uniform hazard FRS generated by the proposed method can reduce the seismic demands significantly (up to 46% as compared to results obtained by the current practice when the RP is set to 10,000 years) to provide an economical solution for seismic design. Furthermore, it overcomes the underestimation of FRS in some frequency ranges by the current practice. Sensitivity study is performed to study the influence of the logarithmic standard deviation and the correlation coefficient between adjacent soil layers of shear-wave velocity.

Wave propagation in a three-dimensional half-space with semi-infinite irregularities

ABSTRACT Dynamic analysis of problems with complex geometries requires utilization of numerical methods. To completely capture the effects of seismic wave propagation in a system, one must consider the structure or irregularity within its encompassing half-space. Correct consideration of half-space in a numerical model is important specially when it comes to cases where the half-space contains semi-infinite irregularities. In this study, a generalized numerical methodology is presented for dynamic analysis of a half-space with semi-infinite irregularities. The methodology is first verified through comparison with analytical solution of known problems. Then the method is employed to solve the dynamic analysis of an arbitrary-shaped existing valley within a half-space under propagating plane harmonic SH wave with different angles of incidence. Results indicate complete capability of the methodology in solving wave propagation problems for complex systems without the usual restrictions of common existing methods.

Seismic Wave Propagation and Basin Amplification in the Wasatch Front, Utah

AbstractGround-motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 Mw 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in the Wasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model (GMM) for Fourier amplitude spectra, which was developed on crustal earthquake records from California and other tectonically active regions. The Wasatch Front records show a significantly different near-source rate of distance attenuation than the BA18 model, which we attribute to differences in (apparent) geometric attenuation. Near-source residuals show a period dependence of this effect, with greater attenuation at shorter periods (T<0.5 s) and a correlation between period and the distance over which the discrepancy manifests (∼20–50 km). We adjusted the recorded ground motions for these regional path effects and solved for station site terms using linear mixed-effects regressions, with groupings for events and stations. We analyzed basin amplification by comparing the site terms with the basin geometry and basin depths from two seismic-velocity models for the region. Sites over the deeper parts of the sedimentary basins are amplified by factors of 3–10, relative to sites with thin sedimentary cover, with greater amplification at longer periods (T≳1 s). Average ground-motion variability increases with period, and long-period variability exhibits a slight increase at the basin edges. These results indicate regional seismic wave propagation effects requiring further study, and potentially a regionalized GMM, as well as highlight basin amplification complexities that may be incorporated into seismic hazard assessments.

Quantifying strong seismic propagation effects in the upper volcanic edifice using sensitivity kernels

In volcanic environments, the correct interpretation of the signals recorded by a seismic station is critical for a determination of the internal state of the volcano. Those signals contain information about both the seismic source and the properties of the path travelled by the seismic wave. Therefore, understanding the path effect is necessary for both source inversions and geophysical investigation of the volcanoes' properties at depth. We present an application of the seismic adjoint methodology and sensitivity kernel analysis to investigate seismic wave propagation effects in the upper volcanic edifice. We do this by performing systematic numerical simulations to calculate synthetic seismograms in two-dimensional models of Mount Etna, Italy, considering different wave velocity properties. We investigate the relationship between different portions of a seismogram and different parts of the structural volcano model. In particular, we examine the influence of known near-surface low-velocity volcanic structure on the recorded seismic signals. Results improve our ability to understand path effects highlighting the importance of the shallowest velocity structure in shaping the recorded seismograms and support recent studies that show that, although long-period seismic events are commonly associated with magma movements in resonant conduits, these events can be reproduced without the presence of fluids. We conclude that edifice heterogeneities impart key signatures on volcano seismic traces that must be considered when investigating volcano seismic sources.

3D NUMERICAL MODELLING OF THE SEISMIC RESPONSE OF THE THESSALONIKI URBAN AREA: THE CASE OF THE 1978 VOLVI EARTHQUAKE

This study aims at showing the numerical modelling of earthquake ground motion in the Thessaloniki urban area, using a 3D spectral element approach. The availability of detailed geotechnical/geophysical data together with the seismological information regarding the relevant fault sources allowed us to construct a large-scale 3D numerical model suitable for generating physics based ground shaking scenarios within the city of Thessaloniki up to maximum frequencies of about 2 Hz. Results of the numerical simulation of the destructive MW6.5 1978 Volvi earthquake are addressed, showing that realistic estimates can be obtained. Shaking maps in terms of ground motion parameters such as PGV are used to discuss the main seismic wave propagation effects at a wide scale.

ON THE SENSITIVITY OF GROUND MOTION PREDICTION EQUATIONS IN GREECE

Ground motion prediction equations, widely known as attenuation relations, are common input for probabilistic and deterministic seismic hazard studies. The construction of a ground motion model to describe such a complex phenomenon as the effects of seismic wave propagation is highly dependable on a number of parameters. The quality and the distribution of strong motion data, which is the original input for the calculation of any ground motion model, can be thought as one of the main parameters that heavily influence the form of ground motion prediction equations. The selected processing scheme, involving significant choices about a series of adjustments and filter specifications, implemented to remove low and high frequency noise, is related with the credibility of the calculated ground motion parameters such as the spectral ordinates. Once a set of response variables for a number of predictors is available, the researcher’s interest is related with the mathematical definition of the ground motion model, in terms of selecting the appropriate parameters and the determination of their coefficients of the equation. Another significant part involves the selection of the optimum solver in order to achieve high confidence level coefficients and a computationally inexpensive solution. Each method should be evaluated through statistics but the researcher should bear in mind that residual analysis and statistical errors, although they can adequately represent the efficiency of the mathematical equations, do not always provide information about where our efforts should lie in terms of further improvement. The scope of this paper is to point out the multi-parametric nature of the construction of ground motion prediction equations and how each of the aforementioned development stages influences the credibility of the proposed attenuation relations.

Seismic wave propagation effects on buried segmented pipelines

This paper deals with seismic wave propagation effects on buried segmented pipelines. A finite element model is developed for estimating the axial pipe strain and relative joint displacement of segmented pipelines. The model accounts for the effects of peak ground strain, shear transfer between soil and pipeline, axial stiffness of the pipeline, joint characteristics of the pipeline, and variability of the joint capacity and stiffness. For engineering applications, simplified analytical equations are developed for estimating the maximum pipe strain and relative joint displacement. The finite element and analytical solutions show that the segmented pipeline is relatively flexible with respect to ground deformation induced by seismic waves and deforms together with the ground. The ground strain within each pipe segmental length is shared by the joint displacement and pipe barrel strain. When the maximum ground strain is higher than 0.001, the pipe barrel strain is relatively small and can be ignored. The relative joint displacement of the segmented pipeline is mainly affected by the variability of the joint pullout capacity and accumulates at locally weak joints.

Numerical Simulation of Seismic Wave Propagation in Different Media

Theory of elastic waves layered homogeneous medium or even medium for the study can not meet the actual demand for seismic exploration, especially for fine rock to construct reservoirs for the study, had to consider small-scale heterogeneity of seismic wave propagation effects. In this thesis, multi-scale model of a complex medium, in ensuring the premise to further improve simulation accuracy simulation efficiency issue, the introduction of a variable grid numerical simulation techniques, and were analyzed for different types of grid difference, establish a different media model simulation results verify the validity of simulation and analyzes its efficiency and accuracy problems.

Solving the complex near‐surface problem using 3D data‐driven near‐surface layer replacement

ABSTRACTIn many land seismic situations, the complex seismic wave propagation effects in the near‐surface area, due to its unconsolidated character, deteriorate the image quality. Although several methods have been proposed to address this problem, the negative impact of 3D complex near‐surface structures is still unsolved to a large extent. This paper presents a complete 3D data‐driven solution for the near‐surface problem based on 3D one‐way traveltime operators, which extends our previous attempts that were limited to a 2D situation. Our solution is composed of four steps: 1) seismic wave propagation from the surface to a suitable datum reflector is described by parametrized one‐way propagation operators, with all the parameters estimated by a new genetic algorithm, the self‐adjustable input genetic algorithm, in an automatic and purely data‐driven way; 2) surface‐consistent residual static corrections are estimated to accommodate the fast variations in the near‐surface area; 3) a replacement velocity model based on the traveltime operators in the good data area (without the near‐surface problem) is estimated; 4) data interpolation and surface layer replacement based on the estimated traveltime operators and the replacement velocity model are carried out in an interweaved manner in order to both remove the near‐surface imprints in the original data and keep the valuable geological information above the datum. Our method is demonstrated on a subset of a 3D field data set from the Middle East yielding encouraging results.

Modelling long-term seismic noise in various environments

The strongest seismic noise, called secondary microseisms, is generated by ocean wave interactions and we model this noise using the theory of Longuet-Higgins generalized to random ocean gravity waves. Noise sources are computed with an ocean wave model that takes into account coastal reflections. Variations of the source locations are consistent with seasonal variations of seismic noise spectra. Noise spectra are modelled over many years for stations representative of various environments such as continent, island and polar area to constrain, for each environment, the parameters involved in the modelling. For each station, we quantify the trade-off between ocean wave coastal reflection and seismic wave attenuation that both affect the amplitude of the seismic spectrum. We show their adjustment and the need, at some stations, for an extra parameter representing the three-dimensional (3-D) seismic wave propagation effects. The long-term analysis demonstrates the stability of the fitted parameters which can be used in future noise studies. The modelling enables to reproduce the frequency content and amplitude of the different noise peaks of seismic spectra. The strongest peaks are generated by deep ocean sources whereas coastal reflections generate numerous smaller sources that contribute to the background noise level. Coastal reflection effects can be neglected only for the Pacific island station PPT. The modelling also reproduces the peculiar noise spectrum variation in Antarctica (station DRV) which is related to the presence of sea ice around the stations.

Seismic imaging in hardrock environments: The role of heterogeneity?

We investigate the effect of petrophysical scale parameters and structural dips on wave propagation and imaging in heterogeneous media. Seismic wave propagation effects within the heterogeneous media are studied for different velocity models with scale lengths determined via stochastic analysis of petrophysical logs from the Matagami mine, Quebec, Canada. The elastic modeling study reveals that provided certain conditions of the velocity fluctuations are met, strong local distortions of amplitude and arrival times of propagating waves are observed as the degree of scale length anisotropy in the P-wave velocity increases. The location of these local amplitude anomalies is related to the dips characterizing the fabric of the host rocks. This result is different from the elliptical shape of direct waves often defined by effective anisotropic parameters used for layered media. Although estimates of anisotropic parameters suggest weak anisotropy in the investigated models, these effective anisotropic parameters often used in VTI/TTI do not sufficiently describe the effects of scale length anisotropy in heterogeneous media that show such local amplitude, travel time, and phase distortions in the wavefields.Numerical investigations on the implications for reverse time migration (RTM) routines corroborate that mean P-wave velocity of the host rocks produces reliable imaging results. Based on the RTM results, we postulate the following: weak anisotropy in hardrock environments is a sufficient assumption for processing seismic data; and seismic scattering effects due to velocity heterogeneity with a dip component is not sufficient to cause mislocation errors of target structures as observed in the discrepancy between the location of the strong seismic reflections associated to the Matagami sulfide orebody and its true location. Future work will investigate other factors that may provide plausible explanations for these mislocation problems, with the objective of providing a mitigation strategy for incorporation into the seismic data processing sequence when imaging in hardrock settings.

Broadband Waveform Modeling of Moderate Earthquakes in the San Francisco Bay Area and Preliminary Assessment of the USGS 3D Seismic Velocity Model

Abstract Recently, the United States Geologic Survey Earthquake Hazards Program developed a 3D seismic velocity model of Northern California based on geology, including a detailed model of the urbanized San Francisco Bay Area. In this study, we report comparisons of observed three-component broadband (0.03–0.25-Hz) waveforms with synthetic seismograms computed with the new 3D model using an elastic finite difference method. We selected a set of 12 moderate earthquakes ( M w 4.0–5.1) that occurred within the greater San Francisco Bay Area, having well-constrained source parameters and broadband recordings with high signal-to-noise ratios. The objective of this study was to investigate how well the 3D velocity model predicts observed waveforms and to identify features of the model that may require revision to improve the waveform fits and predictions of ground motions for future events. We show for the 3 September 2000 Yountville earthquake that reported source parameters accurately predict waveforms at two close strong-motion stations (approximately 10 km from the epicenter). By comparing synthetics for the average 1D model GIL7 (Stidham et al. , 1999) and the 3D structures we show that the effects of seismic wave propagation in the 3D model become important for frequencies at and above 0.1 Hz (periods less than 10 sec). Comparison of observed and synthetic seismograms for the 3D model consistently shows that the model predicts energy arriving earlier than is observed, particularly for the surface waves, indicating that the shear velocities in the upper crust must be reduced. We cross correlated the observed and synthetic waveforms and recorded the delay time and linear correlation for best alignment of the data and delayed synthetic. The results indicate that generally the 3D model predicts the observed waveforms well (mean linear correlations 0.41) and includes features that arise from the interaction of the wave field with 3D structure, especially the major sedimentary basins in San Pablo Bay, San Francisco Bay, Santa Clara Valley, and Livermore Valley. Simple conversion of the observed delay times for optimal alignment suggests shear velocities should be reduced by 4%–5% on average. Based on these findings, we conclude that the model is an excellent first step, suggesting that the overall structure of the model is accurate (i.e., the basin and discontinuity geometry). However, the velocities must be reduced to improve the observed timing of surface-wave arrivals.

The development of seismic reflection sandbox modeling

Analog sandbox models provide cheap, concise data and allow the evolution of geological structures to be observed under controlled laboratory conditions. Seismic physical modeling is used to study the effects of seismic wave propagation in isotropic and anisotropic media, and to improve methods of data acquisition, processing, and interpretation. By combining these two independent modeling techniques, the potential exists to expand the benefits of each method. For seismic physical modeling, the main advantages are that the seismic data collected from these models contain natural variations that cannot be built into conventional solid models, which are machined with predetermined structures. In addition, the cost and construction time to build these models is significantly reduced. For sandbox modeling, the ability to record three-dimensional (3-D) seismic images before the model is manually sectioned for conventional two-dimensional (2-D) structural interpretation allows far more detailed study of subtle 3-D structures than previously possible. In the past other workers have attempted to use unconsolidated sands for seismic physical models, but these attempts have been unsuccessful because of the lack of control or understanding of the natural variations that occur throughout the models. The aim of our research has been to overcome such problems and to develop techniques to alter the acoustic impedance of sand layers, thereby allowing the subsequent ultrasonic seismic recording of 3-D fault systems in sand analog geological models.

Computer animation as a tool to visualize effects of seismic wave propagation inside heterogeneous media

A technique to make computer animations representing the propagation of antiplane shear waves in heterogeneous dissipative media is presented. The aim is to develop a useful tool to better investigate the physics of site effectsin the 2D approximation. We apply this technique to real case studies that were the subject of previous papers. For each case study a movie has been made to illustrate the wavefield time evolution and its interaction with the geological structure. All the movies can be seen and downloaded at the web site http://sigfrido.ingrm.it/movies.html. The paper shows the most representative frames of movies, providing an overview of the role played by the topographic irregularities and the geometry of internal discontinuities in trapping and focusing energy. The details of the dynamics are well visualized through movies. Particular attention is devoted to the representation of simulated ground motion in sediment-filled basins under resonance conditions. Problems related to color scales and frame normalization are analysed and discussed.

2.5-D Numerical Simulation of Acoustic Wave Propagation

—Endeavors to simulate the 3-D seismic wave propagation effects in the 2-D environment have stimulated the development of 2.5-D simulation techniques. Liner (1991) has developed a damped 2.5-D acoustic wave equation using the 3-D Green's function for a constant density medium. This paper presents the finite-difference simulation and study of various numerical artifacts, using Liner's acoustic wave equation. Comparisons of second-order as well as fourth-order accurate 2.5-D and 2-D acoustic wave simulation results have been given. The snapshots at different times and zero off-set response of a salt dome model have been computed and strong reflections and diffraction phases have been reported. Also, the analysis of amplitude behaviors and computational time for Liner's (1991) and Williamson and Pratt's (1995) 2.5-D wave equations, with and without the last term (1/t 2),reveals that this last term is superfluous as suggested by Stockwell (1995). The effectiveness of Sponge transmissive as well as Clayton and Engquist (1980) absorbing boundary conditions has been studied. A modified Ricker wavelet, the second derivative of the convolution of Gaussian function and a polynomial window, has been used as a source. It has been found that the stability condition and the requirement of the number of grid points per wavelength to avoid grid dispersion are the same as for the 2-D acoustic cases.

Effects of seismic wave propagation on a long and narrow building: body wave and surface wave propagation: T. Sugiyama, T. Ishii & M. Kaneko, Computers & Geotechnics, 17(4), 1995, pp 547–564

Effects of seismic wave propagation on a long and narrow building: body wave and surface wave propagation: T. Sugiyama, T. Ishii & M. Kaneko, Computers & Geotechnics, 17(4), 1995, pp 547–564

THE SEISMIC EXPRESSION OF THREE-DIMENSIONAL SANDBOX MODELS

Analogue sandbox models provide cheap, concise data and allow the evolution of geological structures to be observed under controlled conditions in a laboratory. Seismic physical modelling is used to study the effects of seismic wave propagation in isotropic and anisotropic media and to improve methods of data acquisition, processing and interpretation. These two independent geological modelling techniques have been linked for the first time, to combine and expand the existing benefits of each method.Seismic physical modelling to date has employed solid models, constructed with pre-determined structures built into the model. Previous attempts to adapt this technology to unconsolidated materials failed due to the severe energy attenuation of seismic waves in cohesionless grain matrices, and excessive signal scatter due to scaling limitations of the geological feature size to wavelength ratio. This paper presents our research to overcome these problems and thereby allow the successful seismic imaging of sandbox models.A number of techniques have been developed to combine these two independent modelling methods and results show that it is possible to image several layers within the models, demonstrating the potential to interpret complex geological structures within such models. For seismic modelling, the main advantages are that the seismic data collected from these models contain natural variation that cannot be built into solid models, which results in a more realistic image, and the cost and construction time of the models are also dramatically reduced. For sandbox modelling, the recording of seismic data over them allows far more detailed interpretation of the structures than previously possible and also allows direct comparison with field data for the first time, to substantiate or negate an existing interpretation.