scholarly journals Oblique Incidence of Seismic Wave Reflecting Two Components of Design Ground Motion

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
W. J. Cen ◽  
X. H. Du ◽  
D. J. Li ◽  
L. N. Yuan
Keyword(s):  
Free Surface ◽  
Ground Motion ◽  
Oblique Incidence ◽  
Free Field ◽  
P Wave ◽  
Artificial Boundary ◽  
Topography Effect ◽  
Obliquely Incident ◽  
Local Topography ◽  
Incident Waves

The wave field on the artificial boundary was separated into the free field without local topography effect and scattering field induced by local topography effect. The simulation of the free field under obliquely incident waves was conducted. Based on the assumption that the components of design ground motion were treated as the coincidence of oblique P wave and oblique SV wave, the relationship between the oblique input waves and the design ground motion was established in the free field. Further, the contributions to the two components of design ground motion of obliquely incident waves were discussed. The calculation model in time domain was achieved by the combination of the propagation characteristics of obliquely incident waves and the artificial boundary in the free field. The seismic response to the design ground motion was produced on the free surface. The verification of the 2D half-space model under oblique input waves indicated that the wave input method can accurately reflect the design ground motion on the free surface. Application of an earth-rock dam showed that oblique incidence of seismic waves results in significantly different dynamic response compared with the normal incidence. The proposed method can also be employed in the seismic analysis of large span structures with nonuniform ground motion input.

Amplitude effect of the free surface in elastic reverse-time extrapolation

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. S177-S184 ◽  
Author(s):  
Robert Sun ◽  
George A. McMechan
Keyword(s):  
Free Surface ◽  
Computational Model ◽  
P Wave ◽  
Surface Boundary ◽  
Reverse Time ◽  
S Wave ◽  
Elastic Data ◽  
Converted Waves ◽  
Incident Waves ◽  
Time Extrapolation

We evaluate the physical validity of surface boundary conditions of the computational model in reverse-time extrapolation of 3D, three-component (3-C) elastic seismic data acquired at the earth’s free surface by using mathematical derivations and numerical simulations. Reverse-time extrapolation of elastic data assumes that only the incident P- or S-waves are reconstructed during extrapolation into the computational grid. However, superposition of the (upgoing) incident waves and the (downgoing) reflected and converted waves generated at the free surface also is recorded in data acquisition and is input into reverse-time extrapolation. In elastic reverse-time extrapolation, the computational model needs to have an absorbing top boundary. When the 3D, 3-C elastic data are inserted into the computational model during reverse-time extrapolation, the originally incident P- or S-wave is reconstructed. In addition, the free-surface P-to-P reflected and P-to-S converted waves recombine to reconstruct a second incident P-wave, and the free-surface S-to-S reflected and S-to-P converted waves recombine to reconstruct a second incident S-wave. Therefore, 3D elastic reverse-time extrapolation reconstructs the incident waves with displacement amplitudes increased by a fixed factor of exactly two when free-surface reflections and conversions are in the data. In this implementation, reconstructed (virtual) waves propagating upward from the free surface enter an absorbing zone and disappear.

Ground-motion amplification by topographic depressions for incident P wave under acoustic approximation

1977 ◽  
Vol 67 (2) ◽  
pp. 345-352
Author(s):  
Shri Krishna Singh ◽  
Federico J. Sabina
Keyword(s):  
Free Surface ◽  
Half Space ◽  
Ground Motion ◽  
Cylindrical Cavity ◽  
Analytic Solutions ◽  
P Wave ◽  
Saturated Soils ◽  
Ground Motion Amplification ◽  
Topographic Depressions ◽  
Acoustic Approximation

Abstract Ground-motion amplification caused by a semi-spherical and a semi-cylindrical cavity in a half-space for an incident P wave is calculated from analytic solutions under acoustic approximation. We expect this approximation to be valid for materials with a Poisson's ratio near 0.5, e.g., saturated soils. The ground motion is zero at the edges of the cavity and is normal to the free surface. An amplification of about 2 to 3 occurs near the bottom of the cavity for large wavelengths. Detailed numerical results are given for vertical incidence.

scholarly journals Evaluation of Ground Motion Amplification Effects in Slope Topography Induced by the Arbitrary Directions of Seismic Waves

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6744
Author(s):  
Chao Yin ◽  
Wei-Hua Li ◽  
Wei Wang
Keyword(s):  
Ground Motion ◽  
Seismic Waves ◽  
Ground Motions ◽  
Soft Materials ◽  
Artificial Boundary ◽  
P Waves ◽  
Ground Motion Amplification ◽  
Acceleration Amplification ◽  
Slope Topography ◽  
Incident Waves

The incident directions of seismic waves can change the ground motions of slope topography. To elaborate on the influences of the directions of seismic waves, a dynamic analysis of the slope topography was performed. Seismic waves were input using an equivalent nodal force method combined with a viscous-spring artificial boundary. The amplification of ground motions in double-faced slope topographies was discussed by varying the angles of incidence. Meanwhile, the components of seismic waves (P waves and SV waves), slope materials and slope geometries were all investigated with various incident earthquake waves. The results indicated that the pattern of the amplification of SV waves was stronger than that of P waves in the slope topography, especially in the greater incident angels of the incident waves. Soft materials intensely aggravate the acceleration amplification, and more scattered waves are produced under oblique incident earthquake waves. The variations in the acceleration amplification ratios on the slope crest were much more complicated at oblique incident waves, and the ground motions were underestimated by considering only the vertical incident waves. Therefore, in the evaluation of ground motion amplification of the slope topography, it is extremely important to consider the direction of incident waves.

scholarly journals Study on the influence of the seafloor soft soil layer on seismic ground motion

2021 ◽  
Vol 21 (2) ◽  
pp. 577-585
Author(s):  
Jingyan Lan ◽  
Juan Liu ◽  
Xing Song
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Response Spectrum ◽  
Soft Soil ◽  
Free Field ◽  
Soil Layer ◽  
P Wave ◽  
Response Analysis ◽  
Peak Acceleration ◽  
Seismic Response Analysis

Abstract. In the complex medium system of the sea area, the overlying seawater and the surface soft soil have a significant impact on the seafloor ground motion, which brings great seismic risk to the safety of offshore-engineering structures. In this paper, four sets of typical free-field models are constructed and established, comprising a land model, land model with surface soft soil, sea model and sea model with surface soft soil. The dynamic finite-difference method is used to carry out two-dimensional seismic response analysis of a typical free field based on the input forms of P and SV waves. By comparing the seismic response analysis results of four groups of calculation models, the effects of overlying seawater and soft soil on the peak acceleration and acceleration response spectrum are studied. The results show that when an SV wave is input, the peak acceleration and response spectrum of the surface of soft soil on the surface and the seabed surface can be amplified, while the overlying seawater can significantly reduce the ground motion. When the P wave is used, the effect of overlying seawater and soft soil on the peak acceleration and response spectrum of the surface and seabed can be ignored. The peak acceleration decreases first and then increases from the bottom to the surface, and the difference of peak acceleration calculated by four free-field models is not obvious. The results show that the overlying seawater and the surface soft soil layer have little effect on the peak acceleration of ground motion below the surface.

Seismic Response of Gravity Dam under Oblique Incidence of Seismic Waves

2013 ◽  
Vol 838-841 ◽  
pp. 1585-1590
Author(s):  
Li Chen ◽  
Liao Jun Zhang
Keyword(s):  
Seismic Response ◽  
Oblique Incidence ◽  
Seismic Waves ◽  
Near Field ◽  
P Wave ◽  
Gravity Dam ◽  
Response Analysis ◽  
Uniform Motion ◽  
Obvious Effect ◽  
Obliquely Incident

The selection of proper seismic input is essential for seismic response analysis of the gravity dam structures. For the near-field earthquakes, the direction of seismic waves is not always considered as vertical. The non-uniform motion produced by oblique incidence can cause significant influence to the structure. In this study, the obliquely incident method is applied in the finite element model of a typical section of a gravity dam located in southwestern China. The seismic response under obliquely incident of plane P wave and plane SV with different incident angles and tilt directions are discussed. The results show that the oblique incidence has an obvious effect on the seismic response of the gravity dam, and the inconsistence produced by oblique incidence cannot be neglected.

An exact anelastic model for the free-surface relfection of P and S-I waves

1989 ◽  
Vol 79 (3) ◽  
pp. 842-859
Author(s):  
R. D. Borcherdt ◽  
G. Glassmoyer
Keyword(s):  
Free Surface ◽  
Volumetric Strain ◽  
Major Axis ◽  
P Wave ◽  
Reflection Coefficients ◽  
S Wave ◽  
Low Loss ◽  
Surface Reflection ◽  
Pierre Shale ◽  
Homogeneous Wave

Abstract Exact anelastic solutions incorporating inhomogeneous waves are used to model numerically S-I and P waves incident on the free surface of a low-loss anelastic half-space. Anelastic free-surface reflection coefficients are computed for the volumetric strain and displacement components of inhomogeneous wave fields. For the problem of an incident homogeneous S-I wave in Pierre shale, the largest strain and displacement amplitudes for the reflected P wave occur at angles of incidence for which the particle motion for the reflected inhomogeneous P wave is elliptical (minor/major axis = 0.6), the specific absorption (QP−1) is greater (300 per cent) and the velocity is less (25 per cent) than those for a corresponding homogeneous P wave, the direction of phase propagation is not parallel to the free surface, and the amplitude of the wave shows a significant increase with depth (6 per cent in one wavelength). Energy reflection coefficients computed for this low-loss anelastic model show that energy flow due to interaction of the incident and reflected waves reach maxima (30 per cent of the incident energy) near large but nongrazing angles of incidence. For the problem of an incident homogeneous P wave in Pierre shale, the inhomogeneity of the reflected S wave is shown not to contribute to significant variations in wave field characteristics over those that would be expected for a homogeneous wave.

Conditioned Simulation of Ground-Motion Time Series at Uninstrumented Sites Using Gaussian Process Regression

2021 ◽  
Author(s):  
Aidin Tamhidi ◽  
Nicolas Kuehn ◽  
S. Farid Ghahari ◽  
Arthur J. Rodgers ◽  
Monica D. Kohler ◽  
...  
Keyword(s):  
Time Series ◽  
Gaussian Process ◽  
Ground Motion ◽  
San Francisco ◽  
Earthquake Engineering ◽  
Seismic Analysis ◽  
Ground Motions ◽  
Free Field ◽  
Gaussian Process Regression ◽  
Motion Time

ABSTRACT Ground-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.

Three-component analysis of regional seismograms

1990 ◽  
Vol 80 (6B) ◽  
pp. 2032-2052 ◽  
Author(s):  
D. C. Jepsen ◽  
B. L. N. Kennett
Keyword(s):  
Free Surface ◽  
Time Window ◽  
Seismic Station ◽  
P Wave ◽  
Sh Waves ◽  
Near Surface ◽  
Source Discrimination ◽  
Decomposition Scheme ◽  
Phased Array Techniques ◽  
The Stability

Abstract Both phased array techniques for single-component sensors and vectorial analysis of three-component recordings can provide estimates of the azimuth and slowness of seismic phases. However, a combination of these approaches provides a more powerful tool to estimate the propagation characteristics of different seismic phases at regional distances. Conventional approaches to the analysis of three-component seismic records endeavor to exploit the apparent angles of propagation in horizontal and vertical planes as well as the polarization of the waves. The basic assumption is that for a given time window there is a dominant wavetype (e.g., a P wave) traveling in a particular direction arriving at the seismic station. By testing a range of characteristics of the three-component records, a set of rules can be established for classifying much of the seismogram in terms of wavetype and direction. It is, however, difficult to recognize SH waves in the presence of other wavetypes. Problems also arise when more than one signal (in either wavetype or direction) arrive in the same window. The stability and robustness of the classification scheme is much improved when records from an array of three-component sensors are combined. For a set of three-component instruments forming part of a larger array, it is possible to estimate the slowness and azimuth of arrivals from the main array and then extract the relative proportions of the current P-, SV-, and SH-wave contributions to the seismogram. This form of wavetype decomposition depends on a model of near-surface propagation. A convenient choice for hard-rock sites is to include just the effect of the free surface, which generates a frequency-independent operation on the three-component seismograms and which is not very sensitive to surface velocities. This approach generates good estimates of the character of the S wavefield, because the phase distortion of SV induced by the free surface can be removed. The method has been successfully applied to regional seismograms recorded at the medium aperture Warramunga array in northern Australia, and the two small arrays NORESS and ARCESS in Norway, which were designed for studies of regional phases. The new wavefield decomposition scheme provides results in which the relative proportions of P, SV, and SH waves as a function of time can be compared without the distortion imposed by free surface amplification. Such information can provide a useful adjunct to existing measures of signal character used in source discrimination.

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