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Grid dispersion in generating finite-differences synthetic seismograms

Acta Seismologica Sinica(English Edition) 1994年第3期7卷 397-407页

作者： Abdolrahim Javaherian (Institute of Geophysics, the University of Tehran, P. O. Box 14155-4666 Tehran, Islamic Republic of Iran) Institute of Geophysics the University of Tehran Tehran Islamic Republic of Iran

In order to obtain a finite-difference synthetic seismogram, the finite earth model must be subdivided into *** the cell size becomes too large in comparison with wavelength of the source signal, waves disperse with increasing traveltime. This phenomenon is known as grid dispersion. The grid dispersion produces a variation of velocity with different frequencies; that is the higher signal frequencies travel more slowly than the lower signal frequencies. Consequently, substantial tailing of the signal arises with increasing traveltime. This may happpen if: (1) the grid spacing is large; (2) the sampling rate is large; or (3) the source wavelength is too short compared with grid size. In other words, an important parameter in generating finite-difference synthetic seismograms is the number of grid points per wavelength of the source signal. In this paper, it is shown that the frequency of a source function has great effects on grid dispersion when P-Sv coupled waves propagate through elastic models by finite-differences. The two-dimensional elastic models considered in this paper consist of : (1) a normal fault, and (2) a layer over a half-space. This study verifies that, when generating finite-difference synthetic seismograms, the grid dispersion will be reduced to a satisfactory level if the grid points per wavelength at the half-power frequency of the source signal for the lowest velocity of the medium exceeds ten.

关键词： grid dispersion finite differencess synthetic seismograms

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The　optimum　source－time　function　for　generating　finite－difference　synthetic　seismograms

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Acta Seismologica Sinica(English Edition) 1994年第1期7卷 23-31页

作者： Abdolrahim JAVAHERIAN(Institute of Geophysics,the University Of Tehran, P.O.Box 14155-6466 Tehran,Islamic Republic of Iran) Institute of Geophysics the University of Tehran Tehran Islamic Republic of Iran

A source-time function plays an important role in generating finite-difference synthetic *** this regard,we consider the amplitude spectra of five different time *** investigation shows that when the high-frequency signals of the time function carry more power than the main signal,the tailing phenomena would be associated with the main signal which is not desirable in producing finite-difference synthetic *** is illustrated that the time function denoted by is the optimal source-time function among those examined in this paper for generating finite-difference synthetic *** matter is also verified by making finite-difference synthetic seismograms over an elastic earth model consisting of a layer over a half space.

关键词： source-time function finite-difference synthetic seismograms

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Seismic waves in 3-D:from mantle asymmetries to reliable seismic hazard assessment

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Earthquake Science 2014年第5期27卷 567-576页

作者： Giuliano F.Panza Fabio Romanelli Department of Mathematics and Geosciences University of TriesteVia Weiss 434127 TriesteItaly International Center for Theoretical Physics SAND groupVia Weiss 434127 TriesteItaly International Seismic Safety Organization ISSO IG-CEA

A global cross-section of the Earth parallel to the tectonic equator（TE） path,the great circle representing the equator of net lithosphere rotation,shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift *** lowvelocity layer in the upper asthenosphere,at a depth range of 120 to 200 km,is assumed to represent the decoupling between the lithosphere and the underlying *** the TE-perturbed（TE-pert） path,a ubiquitous LVZ,about 1,000-km-wide and 100-km-thick,occurs in the *** existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the ***-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis（NDSHA）,using realistic and duly validated synthetic time series,and generating a data bank of several thousands of seismograms that account for source,propagation,and site ***,with basic selforganized criticality concepts,NDSHA permits the integration of available information provided by the most updated seismological,geological,geophysical,and geotechnical databases for the site of interest,as well as advanced physical modeling techniques,to provide a reliable and robust background for the development of a design basis for cultural heritage and civil *** of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory,and a case-study is *** order to enable a reliable estimation of the ground motion response to an earthquake,three-dimensional velocity models have to be considered,resulting in a new,very efficient,analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.

关键词： 3D Earth - Lithosphere Mantle Seismichazard synthetic seismograms

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Strong Earthquake Sequences in Greece during 2008-2014: Moment Tensor Inversions and Fault Plane Discrimination

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Open Journal of Earthquake Research 2020年第4期9卷 323-348页

作者： Alexandra Moshou Institute of Geodynamics National Observatory of Athens Athens Greece

As is well known, Greece has a significant number of earthquakes each year. Ιn recent years, several earthquakes have occurred in Greece. For this scope, a methodology was used to determine the source parameters. This methodology is based on minimizing the difference between the observed and the synthetic waveforms, using the method Source Parameters Calculation—SPCa [1]. The source parameters, using the proposed methodology, are calculated by comparing observed seismograms and synthetic by inverting data. The synthetics are calculated using the reflectivity method (Kennett, 1983) as implemented by Randall et al. (1994) for a given earth structure. This study includes inversion results for the strongest events that occurred in Greece from 2008 to 2014. For the same events calculated the main fault plane, using the method of Hypocenter Centroid-plot (HC-plot) [2] [3]. This methodology is a simple geometrical method based on the combination between the hypocentral position and the two possible fault planes.

关键词： synthetic seismograms Moment Tensor Inversion Focal Mechanism Regional Data Nodal Planes

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Finite-difference modelling in two-dimensional anisotropic media using a flux-corrected transport technique

Finite-difference modelling in two-dimensional anisotropic m...

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中国科学院地质与地球物理研究所2002学术年会

作者： D.H.Yang~a,E.Liu~b,Z.J.Zhang~c and J.W.Teng~c a.Department of Mathematics.Tsinghua University Beijing 100084,China b.British Geological Survey.Murchison House.West Mains Road.Edinburgh EH9 3LA,UK. c.nstitute of Geology & Geophysics.Chinese Academy of Sciences.Beijing 100101,China

The conventional finite-difference(FD) method often suffers from numerical dispersion when too few samples per wavelength are used or when models have large velocity contrast,or artefacts caused by source at grid *** this paper,we present a fast finite-difference scheme that is based on the application of vectors and matrices in 2-D anisotropic media,and obtain the stability *** method is based on a flux- corrected transport(FCT) technique, originating from hydrodynamics,which can be incorporated in the conventional finite-difference method to eliminate the numerical dispersion and source-generated *** n-times decoupled absorbing boundary condition is used in our ***-component seismograms in a transversely isotropic medium with a vertical symmetry axis(TIV) are generated for two models using the FCT finite-difference *** with the results of the reflectivity method and the conventional FD method without the FCT technique and any absorbing boundary treatments,we conclude that our FCT based FD method can is very accurate and efficient in computing synthetic seismograms in general heterogeneous and anisotropic media.

关键词： anisotropic wave propagation finite-difference method Hux-corrected transport technique synthetic seismograms

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Parallel 3-D simulation of seismic wave propagation nheterogeneous anisotropic media:a grid method approach

Parallel 3-D simulation of seismic wave propagation nheterog...

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中国科学院地质与地球物理研究所2006学术年会

作者： Hongwei Gao and Jianfeng Zhang Institute of Geology and Geophysics,State Key Laboratory of Lithosphere Evolution, Chinese Academy of Sciences,Beijing 100029,China.

This paper presents a parallel numerical technique for modelling wave propagation in 3-D heterogeneous anisotropic *** scheme is developed by following a so-called 3-D grid method of the elastic-isotropic *** proposed parallel algorithm needs small data exchanges between subdomains in contrast to that developed based on other numerical techniques;therefore, it is more suitable for a *** algorithm is implemented on a mesh of mixed tetrahedrons and parallelepipedons,thus providing an accurate description of arbitrary 3-D surface and interface topographies and an easy generation of a non-uniform,unstructured *** unstructured mesh means that the proposed algorithm can reduce the memory requirement by flexibly assigning small grid spacing in regions with lowvelocities and larger grid spacing in regions with higher *** the 3-D grid method,the resulting anisotropic scheme naturally satisfies the free-surface boundary conditions of arbitrary surface *** a result, the near-surface scattering effects can be more accurately *** proposed scheme can handle a general anisotropy without any *** this paper,the transversely isotropic medium with a tilted symmetry axis,as typically caused by a system of parallel cracks or fine layers,is discussed in detail.A paraxial absorbing boundary condition in a 3-D general anisotropic case is also *** with analytical solutions demonstrate the accuracy of the parallel *** 3-D radiation patterns illustrate shear-wave splitting,as predicted by the *** show the generality and flexibility of the algorithm by modelling wave propagation in an anisotropic half-space with a hemispherical crater on the surface and in mixed isotropic/anisotropic models with horizontal and inclined interfaces.

关键词： numerical techniques seismic anisotropy seismic modelling synthetic seismograms seismic wave propagation topography

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