共查询到20条相似文献，搜索用时 31 毫秒
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During development of theoretical methods to compute synthetic seismograms, a new type of wave called S*-wave was discovered by Hron and Mikhailenko. This wave propagates with the shear-wave velocity and can be interpreted as a non-geometrical wave arrival with large amplitudes strongly depending on the depth of a pure P-point source. In this first experimental verification of the existence of S*-waves by means of two-dimensional model-seismics it is demonstrated that: 1. the S*-wave exists and depends on the source distance from the free surface; 2. the S*-wave is generated as an ordinary shear wave on the free surface at the point located directly above the P-source, as illustrated in the synthetic seismograms. The measured seismograms agree remarkably well with the computed ones. 相似文献
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Summary A method of determining simultaneously the moment tensor and source time function in the point source approximation is presented. For trial values of the moment tensor components and of the source time function, parametrized by the sum of overlapping triangles delayed in time, theoretical seismograms can be synthetized and compared with the recorded ones. The iterative procedure determines the adjustment of source parameters until a good correlation of both synthetic and observed records is reached. The Green functions in a horizontally stratified medium are constructed with the use of a modal summation method.The limits of applicability of the algorithm are illustrated by the inversion of four synthetic seismograms constructed for two horizontally stratified models of the structure in Friuli area, Italy. The records constructed for the same structural model as for which the Green functions were computed can be inverted even in the high-frequency range. In the opposite case, when the records and Green functions used corresponded to different structural models, a good correlation of the input records with the final synthetics was obtained for low - pass filtered data only.Additional tests performed with input seismograms contaminated with random noise yielded good resolution of the moment tensor and the duration of the source time function even for a high noise to signal ratio. 相似文献
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E. J. DOUZE 《Geophysical Prospecting》1979,27(3):564-575
Synthetic seismograms are usually computed for reflections from vertical incidence of P waves for a horizontally layered medium. In actual practice the angle of incidence departs from the vertical, as receivers are usually located at some distance from the source. At angles other than the vertical, the conversion of P- to S-wave energy and changes in the reflection coefficient affect the shape of the synthetic seismograms. The effect of non-vertical incidence on synthetic seismograms is examined in this paper. Seismograms at non-vertical incidence have been computed using the plane-wave approach of Haskell (1953) for a layered medium. The use of plane waves is an approximation to the actual case of spherical wavefronts from a surface source. Using plane-wave theory, the expected wave forms as a function of angle of incidence were computed numerically for several simple models. The results indicate that the synthetic seismograms do not change significantly for angles of incidence between o and 25 degrees. For larger angles the changes in the wave forms may be severe. The effect is more pronounced for high-velocity layers than for low-velocity layers. 相似文献
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合成地震图的广义反射透射系数矩阵方法 总被引：3，自引：1，他引：3
简述了在均匀层状介质中，合成地震图的广义反射透射系数矩阵方法，并通过与有人的计算结果对比，检验了经过修改调试后的合成地震图的计算程序。计算与对比表明，经修改调试后的程序对于各种因素，包括震源类型、震源深度、震中、频率和慢度都有较好的普适性，适用于实际的地震波形研究。 相似文献
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V. G. Krishna 《Journal of Seismology》2018,22(6):1395-1408
We present an approach based on controlled source seismology (CSS) methods, especially developed for processing and modeling of the local earthquake seismograms. Record sections of the local earthquake seismograms generated for multiple source depths illuminate the upper crustal velocity structure in the region. Extensive travel times and synthetic seismograms modeling of the observed record sections reveal the P and S velocity structure in the region. The strength of this approach essentially lies with the possibility of validating the upper crustal velocity models inferred in various subregions of the seismogenic region. A redundant and significantly large number of virtual source local earthquake seismogram sections, gathered for multiple source depths and varying source mechanisms in each of the subregions, validate the same set of P and S velocity models in that region. Further, those models are found to generate the synthetic seismograms consistent with the observed sections. The proposed approach effectively utilizes a reliable dataset from a great volume of well-located local earthquake recordings of a state-of-the-art digital seismograph network. Such a dataset of local earthquake seismograms in the Koyna-Warna active earthquake zone is used here to demonstrate this approach and obtained subregion-specific models of upper crustal P and S velocity structure in the epicentral region. The results indicate that the technique presented here is efficient for processing and modeling the local earthquake seismograms and deriving upper crustal velocity models in the seismogenic regions. 相似文献
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Three large deep earthquakes beneath the Sea of Okhotsk are studied using the relative amplitudes of the direct P phase and the surface reflections pP and sP observed on teleseismic long-period WWSSN seismograms. Use of this comprehensive dataset provides a redundancy of information which allows possible deviation of the source mechanism from the double couple model to be studied over a large part of the focal sphere, in a region where previous workers have postulated complex source mechanisms including implosive precursors and multiple events. Focal mechanism solutions derived from the relative amplitudes are used to create synthetic seismograms which further assist the modelling of the source processes of these earthquakes. One of the three earthquakes occurred close to a sequence of complex earthquakes in 1970–1971 and comprises a number of discrete but related subevents, the two main subevents with similar source mechanism orientations, and the latter subevent probably triggered by the first. The other two earthquakes, which occurred further southwest, are similar to each other and their seismograms display features characteristic of the finite size and rupture propagation of the source which enable the source size, geometry and rupture velocity to be estimated. The source moment tensors of all three earthquakes show no significant deviation from a simple double couple and show no evidence of a volumetric component. 相似文献
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MONIKA BREITZKE 《Geophysical Prospecting》1992,40(1):31-70
In spite of a geometrical rotation into radial and transverse parts, two- or three-component in-seam seismic data used for underground fault detection often suffer from the problem of overmoding ‘noise’. Special recompression filters are required to remove this multimode dispersion so that conventional reflection seismic data processing methods, e.g. CMP stacking techniques, can be applied afterwards. A normal-mode superposition approach is used to design such multimode recompression filters. Based on the determination of the Green's function in the far-field, the normal-mode superposition approach is usually used for the computation of synthetic single- and multi-mode (transmission) seismograms for vertically layered media. From the filter theory's point of view these Green's functions can be considered as dispersion filters which are convolved with a source wavelet to produce the synthetic seismograms. Thus, the design of multimode recompression filters can be reduced to a determination of the inverse of the Green's function. Two methods are introduced to derive these inverse filters. The first operates in the frequency domain and is based on the amplitude and phase spectrum of the Green's function. The second starts with the Green's function in the time domain and calculates two-sided recursive filters. To test the performance of the normal-mode superposition approach for in-seam seismic problems, it is first compared and applied to synthetic finite-difference seismograms of the Love-type which include a complete solution of the wave equation. It becomes obvious that in the case of one and two superposing normal modes, the synthetic Love seam-wave seismograms based on the normal-mode superposition approach agree exactly with the finite-difference data if the travel distance exceeds two dominant wavelengths. Similarly, the application of the one- and two-mode recompression filters to the finite-difference data results in an almost perfect reconstruction of the source wavelet already two dominant wavelengths away from the source. Subsequently, based on the dispersion analysis of an in-seam seismic transmission survey, the normal-mode superposition approach is used both to compute one- and multi-mode synthetic seismograms and to apply one- and multimode recompression filters to the field data. The comparison of the one- and two-mode synthetic seismograms with the in-seam seismic transmission data reveals that arrival times, duration and shape of the wavegroups and their relative excitation strengths could well be modelled by the normal-mode superposition approach. The one-mode recompressions of the transmission seismograms result in non-dispersive wavelets whose temporal resolution and signal-to-noise ratio could clearly be improved. The simultaneous two-mode recompressions of the underground transmission data show that, probably due to band-limitation, the dispersion characteristics of the single modes could not be evaluated sufficiently accurately from the field data in the high-frequency range. Additional techniques which overcome the problem of band-limitation by modelling all of the enclosed single-mode dispersion characteristics up to the Nyquist frequency will be mandatory for future multimode applications. 相似文献
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本文通过格林函数反褶积方法，由台湾峡谷附近的记录资料预测峡谷区的强地面运动的时程曲线．峡谷区的理论格林函数应用２．５维ＳＨ混合方法求解．通过格林函数反褶积方法得到的峡谷区费丛１及费丛２台的位移、速度、加速度和实际资料对比，取得了满意结果．计算结果表明，峡谷底部的峰值加速度相对峡谷边缘为最小；在靠近震中的一侧，峡谷的加速度的最大振幅相对比另一侧大．还给出了其余３个台的预测结果，研究了它们的加速度傅里叶谱和反应谱． 相似文献
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The 2008 Wenchuan earthquake occurred in an active earthquake zone, i.e., Longmenshan tectonic zone. Seismic waves triggered
by this earthquake can be used to explore the characteristics of the fault rupture process and the hierarchical structure
of the Earth’s interior. We employ spectral element method incorporated with large-scale parallel computing technology, to
investigate the characteristics of seismic wave propagation excited by Wenchuan earthquake. We calculate synthetic seismograms
with one-point source model and three-point source model respectively. The AK135 model is employed as a prototype of our numerical
global Earth model. The Earth’s ellipticity, Earth’s medium attenuation, and topography data are taken into consideration.
These wave propagation processes are simulated by solving three-dimensional elastic wave governing equations. Three-dimensional
visualization of our numerical results displays the profile of the seismic wave propagation. The three-point source, which
is proposed from the latest investigations through field observation and reverse estimation, can better demonstrate the spatial
and temporal characteristics of the source rupture process than the one-point source. We take comparison of synthetic seismograms
with observational data recorded at 16 observatory stations. Primary results show that the synthetic seismograms calculated
from three-point source agree well with the observations. This can further reveal that the source rupture process of Wenchuan
earthquake is a multi-rupture process, which is composed by at least three or more stages of rupture processes.
Supported by National Basic Research Program of China (Grant No. 2004CB418406), National Natural Science Foundation of China
(Grant Nos. 40774049 and 40474038), and Computer Network Information Center, Chinese Academy of Sciences (Grant No. INF105-SCE-02-12) 相似文献
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We present a new method for the extraction and removal of the source wavelet from the reflection seismogram. In contrast to all other methods currently in use, this one does not demand that there be any mathematically convenient relationship between the phase spectrum of the source wavelet and the phase spectrum of the earth impulse response. Instead, it requires a fundamental change in the field technique such that two different seismograms are now generated from each source-receiver pair: the source and receiver locations stay the same, but the source used to generate one seismogram is a scaled version of the source used to generate the other. A scaling law provides the relationship between the two source signatures and permits the earth impulse response to be extracted from the seismograms without any of the usual assumptions about phase. We derive the scaling law for point sources in an homogeneous isotropic medium. Next, we describe a method for the solution of the set of three simultaneous equations and test it rigorously using a variety of synthetic data and two types of synthetic source waveform: damped sine waves and non-minimum-phase air gun waveforms. Finally we demonstrate that this method is stable in the presence of noise. 相似文献
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An early detection of the presence of rupture directivity plays a major role in the correct estimation of ground motions and
risks associated to the earthquake occurrence. We present here a simple method for a fast detection of rupture directivity,
which may be additionally used to discriminate fault and auxiliary planes and have first estimations of important kinematic
source parameters, such as rupture length and rupture time. Our method is based on the inversion of amplitude spectra from
P-wave seismograms to derive the apparent duration at each station and on the successive modelling of its azimuthal behaviour.
Synthetic waveforms are built assuming a spatial point source approximation, and the finite apparent duration of the spatial
point source is interpreted in terms of rupture directivity. Since synthetic seismograms for a point source are calculated
very quickly, the presence of directivity may be detected within few seconds, once a focal mechanism has been derived. The
method is here first tested using synthetic datasets, both for linear and planar sources, and then successfully applied to
recent Mw 6.2–6.8 shallow earthquakes in Peloponnese, Greece. The method is suitable for automated application and may be
used to improve kinematic waveform modelling approaches. 相似文献
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Synthetic seismograms for finite sources in spherically symmetric Earth using normal-mode summation 
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下载免费PDF全文 Normal-mode summation is the most rapidly used method in calculating synthetic seismograms. However, normal-mode summation is mostly applied to point sources. For earthquakes triggered by faults extending for as long as several 100 km, the seismic waves are usually simulated by point source summation. In this paper, we attempt to follow a different route, i.e., directly calculate the excitation of each mode, and use normal-mode summation to obtain the seismogram. Furthermore, we assume the finite source to be a ‘‘line source' and numerically calculate the transverse component of synthetic seismograms for vertical strike-slip faults. Finally, we analyze the features in the Love waves excited by finite faults. 相似文献
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Correct representation of seismic waveforms propagating through the mantle from a 600 km deep earthquake is presented using graphic interpolation between synthetic seismograms computed across a grid of mantle depths and distances. All torsional normal modes with periods above 12 s are summed to create 72,846 seismograms at depths between the surface and the core-mantle boundary. The resulting time snapshots show the manner by which seismic shear energy propagates around the core away from the source. 相似文献
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B. M. GURBUZ 《Geophysical Prospecting》1982,30(4):432-443
An analytical relationship for the autocorrelation function of an upsweep with high-frequency attenuation is used in the construction of synthetic seismograms. Field experiments were conducted in two areas to investigate the attenuation of upsweep where the near-surface materials were different. The results showed that the attenuation of high frequencies occurs at the source point depending on the near-surface lithology. The attenuation effect is usually neglected in the construction of the input wavelet of synthetic seismograms for Vibroseis data. In this study, the high-frequency attenuation of upsweep was considered in the construction of the input wavelet for the synthetic seismogram in an area where the Vibroseis technique was used. The synthetic seismogram generated in this manner had a better correlation with the Vibroseis section than that of corresponding synthetics using minimum-phase and the unattenuated autocorrelation wavelet of the upsweep. 相似文献
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In the past two decades numerous studies were made to develop and improve the theory and practical computation techniques of synthesizing theoretical seismograms for the model of multi-layered half-space. Today, synthesizing theoretical seismograms in multi-layered half-space is an important tool for understanding the structure of the Earth's interior as well as the seismic source process from well-recorded seismograms data. As part of a review of the state-of-the-art, in this article I shall present a systematic and self-contained theory of elastic waves in multi-layered half-space media based on the developments in the past two decades. 相似文献
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The Gaussian beam method is applied to vertical seismic profiling in 2-D and 3-D models. A simple approach to the computation of Gaussian beam seismograms in the vicinity of structural interfaces is proposed. The effects of (a) the radiation pattern of a point source, (b) non-causal attenuation, (c) transverse inhomogeneities in synthetic seismograms are studied on numerical examples. 相似文献