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Comparison of Seismic Dispersion and Attenuation Models 总被引：2，自引：0，他引：2
The frequency-dependent attenuation of seismic waves causes decreased resolution of seismic images with depth, and the difference in transmission losses induces amplitude variations with offset. Transmission losses may occur due to friction or fluid movement, or may result from scattering in thin-layer. Whatever the physical mechanism, they can often be conveniently described using an empirical formulation wherein the elastic moduli and propagation velocity are complex functions of frequency.We have compiled and compared algebraically and numerically eight different models involving complex velocity: the Kolsky-Futterman model, the power-law model, Kjartansson's model, Müller's model, Azimi's second and third model, the Cole-Cole model, and the standard linear-solid model.For two different parameter sets, the attenuation and phase velocity are computed in the seismic frequency band, and the plane-wave propagation of a Ricker wavelet for the other models is compared with that for the Kolsky-Futterman model. The first parameter set consists of parameters for each of the models calculated from expressions given in the appendix. These expressions make the different models behave similarly to the KF model. The second parameter set consists of model parameters that are numerically adapted to the KF model.By selecting proper parameters, all models, except the standard linear-solid model, show behavior similar to that of the Kolsky-Futterman model. The SLS model behaves differently from the other models as the frequency goes to zero or infinity. Broadband measurement data is needed to select a specific model for a given seismic experiment. 相似文献
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Studia Geophysica et Geodaetica - 相似文献
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Studia Geophysica et Geodaetica - 相似文献
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. Toverud 《Journal of Geochemical Exploration》1987,28(1-3)
Regional exploration for pegmatite hosted Sn-mineralization in Sweden by LKAB Prospektering has, since the early 1980s, generally been based on the use of heavy-mineral concentrates from till collected by roadside sampling. The average sampling density has been 0.5–1.0 sample/km2, but with an uneven distribution of sample points within areas investigated.Planning of the regional sampling grid in this study has been based on a statistical analysis to answer the following question: What sample density and grid-spacing should be used to hit an anomalous target with the highest possible probability.The statistical analysis indicates that using a rectangular grid, 750 × 1,500 m (0.88 sample/km2), the probability of intersecting an anomalous target is 100%. Heavy-mineral till concentrate sampling using this grid design in northern central Sweden in 1981 revealed one single, extremely high sample with 4,622 ppm Sn indicating mineralization in the area north of the village of Järkvissle.In 1982–1983, while boulder tracing up-ice from the anomalous regional sample point, cassiterite and spodumene-bearing boulders and outcrops were found. Two parallel mineralized pegmatites within an area of approximately 5,000 m2 with grades of 0.04–0.07% Sn and 0.40–0.92% Li2O have recently been located NW of Järkvissle.Semi-regional (250 × 500 m) and local (20 × 20–160 m) sampling of till gave some anomalous values of Sn and Li in concentrates, which to some extent could be correlated with mineralized boulders and outcrops, and also indicated new targets for drilling.The results from a simplified sample preparation technique for heavy-mineratl till concentrates show that a new device, named the Goldhound, can be used in future geochemical prospecting for Sn and Li in Sweden. 相似文献
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ivind Toverud 《Journal of Geochemical Exploration》1989,32(1-3)
In 1982 a reconnaissance geochemical till-sampling survey covering a 37,780-km2 area was performed by Terra Swede AB and Jämtlands Mineral AB in the county of Jämtland in upper central Sweden, using a sampling density of 1 sample per 39.1 km2. The western part of the study area is underlain by rocks of the Caledonides (predominated by Cambrian-Silurian sediments) whereas in the central and eastern parts Precambrian granite, gneiss, pegmatite, diabase and metagraywacke predominate. The area is covered by a relatively continuous cover of till. At least three different ice directions are indicated by glacial striae. Till is covered by glaciofluvial material locally, and where the latter was recognized samples were not collected. Till samples are taken from the C-horizon of podsolic soils at a depth of 0.5–1.0 m. Samples weighing 0.59 g were analyzed by neutron activation analysis after sieving to minus 0.5 mm (35 mesh). 相似文献
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. Toverud 《Journal of Geochemical Exploration》1984,21(1-3)
Since the late part of the 19th century prospecting for W in the western world has been based mainly on the mechanical concentration of heavy minerals in sediments (panning), followed by visual and chemical analyses of the heavy-mineral fraction. Since the early 1970's, W prospecting in Sweden has been based on the use of heavy-mineral concentrates from till.In tests performed in a scheelite-mineralized area in the Bergslagen area of central Sweden, samples from the A- and C-horizon of the podzolic profile have been collected along grid lines across the ore as well as down-ice along the direction of final glacial transport from the ore. The purpose of the study was to test which sample types should be used in geochemical prospecting for W in the region.The results show that all the sample types studied can be used in geochemical prospecting for W in southern central Sweden. The heavy-mineral concentrate of till is primarily recommended for use at a regional and local scale. Humus is given the lowest priority of the sample types studied because of the poor analytical reproducibility for some samples with high values of W. 相似文献
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