| 3-D SURFACE TOPOGRAPHY BOUNDARY CONDITIONS IN SEISMIC WAVE MODELING, |
FEB 2002 |
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| Authors:
STIG HESTHOLM; BENT RUUD; MARK MORAN; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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 | (U) THIS PAPER DISCUSSES SIMULATION OF POINT SOURCES AT THE SURFACE OF A HOMOGENEOUS MEDIUM WITH A PLANE SURFACE COMTAINING A HILL AND A TRENCH, OUTLINING THE MAIN FEATURES. THE PAPER PRESENTS RESULTS USING PARAMETERS TYPICAL OF TELESEISMIC EARTHQUAKES AND EXPLOSIONS IN AN AREA OF REAL TOPOGRAPHY. THE PAPER SHOWS THE NUMERICAL DISCRETIZATION OF THE FREE SURFACE TOPOGRAPHY BOUNDARY CONDITIONS AS WELL AS A SPATIALLY UNCONDITIONAL STABILITY OF THE RESULTING ... |
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| Characterization of Seismic Sources Using Empirical Green's Functions |
21 NOV 97 |
67 pages |
| Authors:
Shirley A. Rieven; William L. Rodi; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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 | Our work on the 1993 micro earthquake swarm at the Larderello geothermal field suggests that the most significant obstacle to the practical application of correlation techniques, such as EGFs or relative event location for seismic events recorded at regional distances, is due to the degree of waveform complexity that is related solely to scattering effects along the path. In this study, we showed that despite similar focal mechanisms and a ... |
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| Research on Seismic Monitoring at Regional Distances |
10 SEP 97 |
88 pages |
| Authors:
M. Imhof; B. Nolte; W. Rodi; M. N. Toksoz; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| We report two studies related to numerical modeling of seismic wave generation and propagation. In the first, we use a 2-D multiple multipole method to model seismic wave radiation from nuclear explosions in and near underground cavities. Our modeling results are used to interpret seismograms recorded during the Non-Proliferation Experiment (NPE), which occurred near a large complex of tunnels and cavities. Synthetic seismograms for a simplified NPE ... |
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| Applications of Parallel Computing Algorithms to Three-Dimensional Modeling of Seismic Waves Generated by Complex Sources in Homogeneous Media |
15 JAN 97 |
21 pages |
| Authors:
Charles G. Doll Jr.; Joseph R. Matarese; Bertram Nolte; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| We describe a hardware upgrade that was performed on the nCUBE 2 massively parallel computer at MIT's Earth Resources Laboratory. The upgrade involved the installation of additional memory, additional disk space, and an additional small nCUBE 2 computer. The reason for performing the upgrade was to provide ERL with a computational environment suitable for conducting large-scale 2-D and 3-D wave propagation simulations. We also describe two recent projects that were ... |
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| Research on Seismic Monitoring at Regional Distances |
15 OCT 96 |
87 pages |
| Authors:
Wenjie Dong; Richard L. Gibson Jr.; Matthias G. Imhof; M. N. Toksoez; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| We report two studies related to numerical modeling of seismic wave generation and propagation. In the first, numerical calculations of seismic wave scattering using the multiple multipole technique are compared to laboratory data that we collected in an ultrasonic experiment. The results demonstrate the validity of the multiple multipole approach for seismic wave propagation modeling. The second study investigates seismic radiation from explosively loaded cavities in isotropic and transversely isotropic ... |
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| Basic Research in Nuclear Test Monitoring: Explosions in Non-Spherical Cavities: Investigations of Enhanced Backscattering |
01 JAN 94 |
103 pages |
| Authors:
Batakrishna Mandal; Craig A. Schultz; Wenjie Dong; M. N. Toksoez; William Rodi; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| We report on two studies. The first is a theoretical study of the seismic radiation from explosions detonated in finite cylindrical tunnels embedded in a homogeneous, isotropic, elastic medium. We developed a frequency domain boundary element/discrete wavenumber algorithm to model the seismic wavefields from such sources, and applied the algorithm to study two specific cases of explosion sources-nuclear and non-nuclear. Our calculations show different source radiation patterns between the two ... |
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| Regional Seismograms: Attenuation and Scattering |
06 MAR 92 |
364 pages |
| Authors:
M. N. Toksoz; E. E. Charrette; N. Cheng; A. M. Dainty; B. Mandal; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The objective of this study was to examine the influence of attenuation and scattering on regional high frequency seismograms. This report consists of a Ph.D. thesis, a paper, and three preprints of papers either submitted or in preparation, on work supported by this project; they include both basic work on attenuation, scattering and anisotropy, and applications to regional seismograms. The Ph.D. thesis discusses the application of the finite difference method ... |
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| Research in Regional Seismology: The Effect of Anisotropy |
19 NOV 91 |
84 pages |
| Authors:
M. N. Toksoz; Richard L. Gibson Jr; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The objective of this study is to examine the influence of fracturing and anisotropy in the source medium or near the source of radiation, especially the generation of SV and SH. One effect is scattering near the source. We present a ray-Born method for the computation of scattered wavefields in a general 3-D, anisotropic medium. This approach applied ray methods to the computation of Green's tensors for a background earth ... |
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| Seismic Wave Propagation, Attenuation and Scattering over Regional Distances |
11 DEC 89 |
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| Authors:
Nafi Toksoez; Ari Ben-Menahem; Edmond E. Charrette; Anton M. Dainty; Richard L. Gibson Jr; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The objective of this project was to conduct basic research on the propagation of seismic energy at regional (100-1000 km) distances for purposes of monitoring underground nuclear explosions. The problems studied were the coherency of the seismic S phases, especially Lg, and the implications in terms of the scattering properties of the earth medium; and scattering from anisotropic inclusions. This Final Report consists of preprints of two papers on these ... |
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| Analysis of Regional Phases Using Three-Component Data |
20 NOV 89 |
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| Authors:
M. Nafi Toksoez; Ari Ben-Menahem; Anton M. Dainty; Batakrishna Mandal; Michael Prange; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The objective of this project was to conduct basic research on the propagation of seismic energy at regional (100 to 1000 km) distances for purposes of monitoring underground nuclear explosions. The problems studied were scattering of seismic body waves by rough interfaces, the effect of anisotropic media on the seismic radiation from sources embedded in them, and the attenuation of crustal phases. This Final Report consists of preprints of four ... |
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| Analysis of Regional Phases Using Three Component Data |
28 NOV 88 |
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| Authors:
Michael Prange; M. N. Toksoz; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| A method is presented for computing three-dimensional seismic wave scattering from a rough interface. It is derived using a perturbation approach which requires interface height perturbations to be small relative to the wavelengths of scattered waves, and interface slope perturbations to be much less than one. These validity conditions are based on an order of error analysis of the truncation of the perturbation series. Comparison of reflection and transmission coefficients ... |
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| Influence of Scattering on Seismic Waves |
08 AUG 88 |
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| Authors:
M. N. Toksoz; Anton M. Dainty; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Work on this contract examined two subjects, the analysis of seismic data using the NORESS array in southern Norway and the attenuation properties of the crust. This document consists of two preprints. The first, 'Phase velocity estimation of diffusely scattered waves deals with work at NORESS which was partly carried out under a previous contract, partly in conjunction with the Lawrence Livermore National Laboratory and partly under this contract. The ... |
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| Influence of Scattering on Seismic Waves: Velocity and Attenuation of the Upper Crust in Southeast Maine |
21 MAR 88 |
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| Authors:
Edmund Reister; Anton M. Dainty; M. N. Toksoez; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Rg and Pg velocities and Rg attenuation have been examined for the Central Merrimack Synclinorium and nearby regions in southeastern Maine using digital records from a seismic refraction experiment. Determination of Rg group velocities and Pg travel times indicates that both lateral variations and azimuthal anisotropy are present in the study area. The axes of the axes of the azimuthal velocity anisotropy appear to lie along and perpendicular to the ... |
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| Influence of Scattering on Seismic Waves: Physical Mechanisms Contributing to Attenuation in the Crust |
30 SEP 87 |
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| Authors:
M. N. Toksoez; Ru-Shan Wu; Denis P. Schmitt; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data, coda waves and strong motion attenuation measurements in the northeastern United States and Canada and theoretical models. The relative contributions to attenuation of anelasticity of crustal rocks (constant Q), fluid flow and scattering are evaluated. Scattering is found to be strong with albedo ... |
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| Teleseismic Waveform Modeling Incorporating the Effects of Known Three- Dimensional Structure Beneath the Nevada Test Site |
08 JUN 87 |
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| Authors:
Vernon F. Cormier; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The pattern of teleseismic amplitudes from underground nuclear tests has been found to have strong variations as a function of location within a test site. Forward modeling of body waves in known three-dimensional structures beneath seismic sources is used to investigate the effects of such structures on teleseismic amplitudes and to determine the structural resolution necessary to formulate amplitude corrections for variations in source site and recording networks. Three-dimensional structures ... |
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| Teleseismic Waveform Modeling Incorporating the Effects of Known Three- Dimensional Structure Beneath the Nevada Test Site |
02 JAN 87 |
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| Authors:
Vernon F. Cormier; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The focusing and defocusing of telemseismic P waves predicted by a known (Taylor, 1983) three-dimensional structure beneath the Nevada Test Site is calculated by dynamic ray tracing and superposition of Gaussian beams. The 20 to 100 km scale lengths of this model, having velocity fluctuations of several per cent, account for a factor of three fluctuations in the azimuthal pattern of P amplitudes. Since similar sized scale lengths and intensities ... |
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| Influence of Scattering on Seismic Waves |
OCT 86 |
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| Authors:
Anton M. Dainty; M. N. Toksoez; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Tests have been carried out to find sources of noise and velocity bias in a new array analysis method, the wavenumber spectrum, which has been used at NORESS to detect diffuse components of teleseismic coda. Noise problems have been analysed by using subarrays and identified as being due to loss of coherence between signals at sensors of given spacing as frequency increases. Velocity bias has been investigated using synthetic signals ... |
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| Teleseismic Waveform Modeling Incorporating the Effects of Known Three- Dimensional Structure Beneath the Nevada Test Site |
14 APR 86 |
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| Authors:
Vernon F. Cormier; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Calculations were performed in 3-D models of the upper 75 - 100 km. of the crust ad mantle beneath the NORSAR array, a model for a region in the northerm California (Zandt, 1981), and a model generated by random perturbations to a 1-D velocity structure. In both the NORSAR and Zandt models, azimuthal variations in travel time were found to be on the order of a factor of 2 and ... |
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| Development of Ultrasonic Modelling Techniques for the Study of Seismic Wave Scattering due to Crustal Inhomogeneities |
MAR 86 |
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| Authors:
M. N. Toksoz; Anton M. Dainty; Edmond E. Charrette III; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Scattering of Rayleigh waves from surface features was investigated using three-dimensional ultrasonic models at frequencies near 1 MHz and two dimensional finite difference calculations. Models were constructed of aluminum blocks and an aluminum powder-epoxy composite of lower density and seismic velocity. The aluminum has similar seismic velocities and density to igneous and metamorphic rocks while the composite is similar to sedimentary materials. Kilometers in the earth are scaled to millimeters ... |
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| Development of Ultrasonic Modelling Techniques for the Study of Seismic Wave Scattering Due to Crustal Inhomogeneities |
MAR 86 |
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| Authors:
M. N. Toksoz; Anton M. Dainty; Edmond E. Charrette III; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| The scattering of Rayleigh waves form surface features has been investigated using three dimensional ultrasonic models at frequencies near 1 MHz and two-dimensional finite difference calculations. The models were constructed of aluminum blocks and an aluminum powder epoxy composite of lower density and seismic velocity. The aluminum has similar seismic velocities and density to igneous and metamorphic rocks while the composite is similar to sedimentary materials. Kilometers in the earth ... |
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| Teleseismic Waveform Modeling Incorporating the Effects of Known Three- Dimensional Structure Beneath the Nevada Test Site |
22 OCT 85 |
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| Authors:
Vernon F. Cormier; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| Seismograms were synthesized by the Gaussian beam method and ray trajectories were plotted for a plane wave incident on a 3-D structure obtained from block inversion of teleseismic travel times observed at a local array in central California. The amplitude variations for the given profile are smaller than the order of magnitude variations typically observed. Since amplitudes are sensitive to smaller scale velocity features than travel times, this may indicate ... |
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| Effects of Heterogeneities on the Propagation, Scattering and Attenuation of Seismic Waves and the Characterization of Seismic Source |
85 |
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| Authors:
Keiiti Aki; Vernon F. Cormier; M. N. Toksoz; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| During this reporting period work was completed on testing alternative measures of body wave magnitude. It was found that alternative measures of body waves magnitude often exhibit as much scatter as classical measures of magnitude, although coda magnitudes usually have slightly less scatter than spectral and classical magnitudes. In the cases investigated, these differences were usually not statistically significant. Another completed task was an investigation of the intrinsic attenuation of ... |
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| Effects of Heterogeneities on the Propagation, Scattering and Attenuation of Seismic Waves and the Characterization of Seismic Source |
30 JUN 1984 |
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| Authors:
K. Aki; V. F. Cormier; M. N. Toksoz; MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB
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| This study has examined the attenuation of local/regional S codas from 0.25 Hz to Hz in the Hindu Kush region. A goal study was to separate the relative contribution of scattering versus intrinsic anelasticity to the attenuation of coda waves. Coda attenuation has been analyzed in the frequency domain using a radiative transfer equation technique, which includes multiple scattering, and in the time domain using weak and strong scattering approximations. ... |
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