A Coupled Method of Spectral Element and Normal Mode: A Powerful Tool for Modeling the Seismic Waves Propagation in the Anisotropic D″ Region

2013 ◽  
Vol 56 (2) ◽  
pp. 148-159
Author(s):  
ZHAO Ming ◽  
ZHAO Liang ◽  
YANN CAPDEVILLE
Keyword(s):  
Normal Mode ◽  
Seismic Waves ◽  
Spectral Element ◽  
Coupled Method ◽  
D Region ◽  
Waves Propagation ◽  
Mode A

scholarly journals Numerical modeling of seismic waves by discontinuous spectral element methods

2018 ◽  
Vol 61 ◽  
pp. 1-37 ◽  
Author(s):  
Paola F. Antonietti ◽  
Alberto Ferroni ◽  
Ilario Mazzieri ◽  
Roberto Paolucci ◽  
Alfio Quarteroni ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Discontinuous Galerkin ◽  
Large Scale ◽  
Seismic Waves ◽  
Spectral Element ◽  
Fully Discrete ◽  
Time Marching ◽  
Space Discretization ◽  
Large Earthquakes

We present a comprehensive review of Discontinuous Galerkin Spectral Element (DGSE) methods on hybrid hexahedral/tetrahedral grids for the numerical modeling of the ground motion induced by large earthquakes. DGSE methods combine the exibility of discontinuous Galerkin meth-ods to patch together, through a domain decomposition paradigm, Spectral Element blocks where high-order polynomials are used for the space discretization. This approach allows local adaptivity on discretization parameters, thus improving the quality of the solution without affecting the compu-tational costs. The theoretical properties of the semidiscrete formulation are also revised, including well-posedness, stability and error estimates. A discussion on the dissipation, dispersion and stability properties of the fully-discrete (in space and time) formulation is also presented. Here space dis-cretization is obtained based on employing the leap-frog time marching scheme. The capabilities of the present approach are demonstrated through a set of computations of realistic earthquake scenar-ios obtained using the code SPEED (http://speed.mox.polimi.it), an open-source code specifically designed for the numerical modeling of large-scale seismic events jointly developed at Politecnico di Milano by The Laboratory for Modeling and Scientific Computing MOX and by the Department of Civil and Environmental Engineering.

scholarly journals Delamination Localization in Sandwich Skin Using Lamb Waves by Finite Element Method

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Salah Nissabouri ◽  
Mhammed El allami ◽  
El Hassan Boutyour ◽  
Ahmed Errkik
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Lamb Waves ◽  
Arrival Times ◽  
Localization Method ◽  
Waves Propagation ◽  
Signal Changes ◽  
2D Fft ◽  
Mode A ◽  
Element Method

In this work we model by finite element method (FEM) the Lamb waves’ propagation and their interactions with symmetric and asymmetric delamination in sandwich skin. The simulations were carried out using ABAQUS CAE by exciting the fundamental A0 Lamb mode in the frequency 300 kHz. The delamination was then estimated by analysing the signal picked up at two sensors using two technics: Two-Dimensional Fast Fourier Transform (2D-FFT) to identify the propagating and converted modes, and wavelet transform (WT) to measure the arrival times. The results showed that the mode A0 is sensible to symmetric and asymmetric delamination. Besides, based on signal changes with the delamination edges, a localization method is proposed to estimate the position and the length of the delamination. In the last section an experimental FEM verification is provided to validate the proposed method.

Three-Dimensional Simulations of Strong Ground Motion in the Shidian Basin

2014 ◽  
Vol 501-504 ◽  
pp. 1447-1452
Author(s):  
Yan Yan Yu ◽  
Qi Fang Liu
Keyword(s):  
Surface Wave ◽  
Ground Motion ◽  
Seismic Waves ◽  
Three Dimensional ◽  
Spectral Element ◽  
Low Velocity ◽  
Computing Technique ◽  
Soil Deposits ◽  
Basin Edge ◽  
The Impact

Seismic response of the Shidian basin to moderate scenario earthquake is investigated considering 3D basin model incorporated with real topography by using the spectral-element method and parallel computing technique. The wave propagation process, the generation of surface wave, and the impact of soil deposits velocity to the basin-induced surface wave are studied in this paper. The results show that the amplification behavior of the basin is the interactions of basin geometry and low velocity soil deposits. First, locally small hollows in the basin are apt to trap seismic waves and produce much stronger ground motion, basin edge and areas with deep sediments are also characterized with large amplification. Then, basin with softer soil deposits produces stronger surface waves with lower propagation velocity and higher mode.

Influence of Snow Cover on the Seismic Waves Propagation

2017 ◽  
pp. 730-736 ◽  
Author(s):  
Gyulnara Voskoboynikova ◽  
Kholmatzhon Imomnazarov ◽  
Aleksander Mikhailov ◽  
Jian-Gang Tang
Keyword(s):  
Snow Cover ◽  
Seismic Waves ◽  
Waves Propagation

Flow instabilities in the wake of a circular cylinder with parallel dual splitter plates attached

2019 ◽  
Vol 874 ◽  
pp. 299-338 ◽  
Author(s):  
Rui Wang ◽  
Yan Bao ◽  
Dai Zhou ◽  
Hongbo Zhu ◽  
Huan Ping ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Rear Surface ◽  
Three Dimensional ◽  
Spectral Element ◽  
Cylinder Wake ◽  
Flow Topology ◽  
Weakly Nonlinear ◽  
Plate Length ◽  
Splitter Plates ◽  
Mode A

In this paper, instabilities in the flow over a circular cylinder of diameter $D$ with dual splitter plates attached to its rear surface are numerically investigated using the spectral element method. The key parameters are the splitter plate length $L$, the attachment angle $\unicode[STIX]{x1D6FC}$ and the Reynolds number $Re$. The presence of the plates was found to significantly modify the flow topology, leading to substantial changes in both the primary and secondary instabilities. The results showed that the three instability modes present in the bare circular cylinder wake still exist in the wake of the present configurations and that, in general, the occurrences of modes A and B are delayed, while the onset of mode QP is earlier in the presence of the splitter plates. Furthermore, two new synchronous modes, referred to as mode A$^{\prime }$ and mode B$^{\prime }$, are found to develop in the wake. Mode A$^{\prime }$ is similar to mode A but with a quite long critical wavelength. Mode B$^{\prime }$ shares the same spatio-temporal symmetries as mode B but has a distinct spatial structure. With the exception of the case of $L/D=0.25$, mode A$^{\prime }$ persists for all configurations investigated here and always precedes the transition through mode A. The onset of mode B$^{\prime }$ occurs for $\unicode[STIX]{x1D6FC}>20^{\circ }$ with $L/D=1.0$ and for $L/D>0.5$ with $\unicode[STIX]{x1D6FC}=60^{\circ }$. The characteristics of all the transition modes are analysed, and their similarities and differences are discussed in detail in comparison with the existing modes. In addition, the physical mechanism responsible for the instability mode B$^{\prime }$ is proposed. The weakly nonlinear feature of mode B$^{\prime }$, as well as that of mode A$^{\prime }$, is assessed by employing the Landau model. Finally, selected three-dimensional simulations are performed to confirm the existence of these two new modes and to investigate the nonlinear evolution of the three-dimensional modes.

scholarly journals Investigating the seismic structure and visibility of dynamic plume models with seismic array methods

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S167-S194
Author(s):  
Fabienne Stockmann ◽  
Laura Cobden ◽  
Frédéric Deschamps ◽  
Andreas Fichtner ◽  
Christine Thomas
Keyword(s):  
Seismic Waves ◽  
Data Sets ◽  
Mantle Plumes ◽  
Seismic Structure ◽  
Optimum Frequency ◽  
Seismic Scattering ◽  
Out Of Plane ◽  
Waveform Modelling ◽  
D Region ◽  
Incoming Energy

SUMMARY Mantle plumes may play a major role in the transport of heat and mass through the Earth, but establishing their existence and structure using seismology has proven challenging and controversial. Previous studies have mainly focused on imaging plumes using waveform modelling and inversion (i.e. tomography). In this study we investigate the potential visibility of mantle plumes using array methods, and in particular whether we can detect seismic scattering from the plumes. By combining geodynamic modelling with mineral physics data we compute ‘seismic’ plumes whose shape and structure correspond to dynamically plausible thermochemical plumes. We use these seismic models to perform a full-waveform simulation, sending seismic waves through the plumes, in order to generate synthetic seismograms. Using velocity spectral analysis and slowness-backazimuth plots, we are unable to detect scattering. However at longer dominant periods (25 s) we see several arrivals from outside the plane of the great circle path, that are consistent with an apparent bending of the wave front around the plume conduit. At shorter periods (15 s), these arrivals are less obvious and less strong, consistent with the expected changes in the waves' behaviour at higher frequencies. We also detect reflections off the iron-rich chemical pile which serves as the plume source in the D″ region, indicating that D″ reflections may not always be due to a phase transformation. We suggest that slowness-backazimuth analysis may be a useful tool to locate mantle plumes in real array data sets. However, it is important to analyse the data at different dominant periods since, depending on the width of the plume, there is probably an optimum frequency band at which the plume is most visible. Our results also show the importance of studying the incoming energy in all directions, so that any apparently out-of-plane arrivals can be correctly interpreted.

scholarly journals 2D full-waveform modeling of seismic waves in layered karstic media

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. T25-T34 ◽  
Author(s):  
Yingcai Zheng ◽  
Adel H. Malallah ◽  
Michael C. Fehler ◽  
Hao Hu
Keyword(s):  
Seismic Waves ◽  
Finite Size ◽  
Spectral Element ◽  
Seismic Wave Propagation ◽  
Complex Model ◽  
Waveform Modeling ◽  
Frequency Space ◽  
Full Waveform ◽  
Matrix Scheme ◽  
Element Method

We have developed a new propagator-matrix scheme to simulate seismic-wave propagation and scattering in a multilayered medium containing karstic voids. The propagator matrices can be found using the boundary element method. The model can have irregular boundaries, including arbitrary free-surface topography. Any number of karsts can be included in the model, and each karst can be of arbitrary geometric shape. We have used the Burton-Miller formulation to tackle the numerical instability caused by the fictitious resonance due to the finite size of a karstic void. Our method was implemented in the frequency-space domain, so frequency-dependent [Formula: see text] can be readily incorporated. We have validated our calculation by comparing it with the analytical solution for a cylindrical void and to the spectral element method for a more complex model. This new modeling capability is useful in many important applications in seismic inverse theory, such as imaging karsts, caves, sinkholes, and clandestine tunnels.

Impact of the Ice Cover onto Seismic Waves' Propagation in Shallow Arctic Water

2015 ◽  
Author(s):  
V.A. Tcheverda ◽  
V.G. Khaidukov ◽  
V.V. Lisitsa ◽  
G.V. Reshetova
Keyword(s):  
Seismic Waves ◽  
Ice Cover ◽  
Arctic Water ◽  
Waves Propagation
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