Comparison of Seismic Dispersion and Attenuation Models   总被引：2，自引：0，他引：2  

Ursin  Björn  Toverud  Tommy 《Studia Geophysica et Geodaetica》2002,46(2):293-320

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   

Erratum: Comparison of Seismic Dispersion and Attenuation Models: Stud. Geophys. Geod., 46(2002), 293-320     

Ursin  Björn  Toverud  Tommy 《Studia Geophysica et Geodaetica》2002,46(4):809-809

Studia Geophysica et Geodaetica -  相似文献   

A new map of glacigenic features and glacial landsystems in central mainland Nunavut,Canada     

Isabelle McMartin  Pierre-Marc Godbout  Janet E. Campbell  Tommy Tremblay  Pouran Behnia 《Boreas: An International Journal of Quaternary Research》2021,50(1):51-75

A new digital map of glacial geomorphic features and interpreted glacial landsystems was produced for an area covering ~415 000 km² in the Keewatin Sector of the Laurentide Ice Sheet (LIS) in Nunavut. The map integrates information from previous surficial geology maps and >14 000 field stations, and is significantly improved by the detailed inventory of ~152 000 glacigenic features using high-resolution ArcticDEM data and Landsat 8 imagery. From this, we identify and map coherent patterns of landform development (landsystems) between the Manitoba border and the Arctic coast, many of which are entirely new and others that are significantly modified or updated. In particular, we recognize six separate ice streams, including one probable remnant ice stream, and we delineate numerous palimpsest streamlined landscapes with associated ice-flow trends and relative ages. A continuum of relict terrains with varying basal ice thermal conditions is mapped for the first time in the ice divide migration zone between Baker Lake and Wager Bay. In addition, deglacial cold-based retreat terrains and preserved warm-based landscapes unaffected by younger glacial events have been identified. These new georeferenced, multi-scale data sets and interpreted glacial landsystems provide a comprehensive framework to strengthen reconstructions of the glacial history and dynamics of one of the largest ice domes of the LIS, identify distinct glacial sediment transport paths for applications to mineral exploration, and test numerical modelling of the LIS in support of climate change studies and long-term evolution of modern ice sheets.  相似文献   

Rock bursting phenomena in a superficial rock mass in southern central Sweden   总被引：1，自引：0，他引：1  

Anders Carlsson  Tommy Olsson 《Rock Mechanics and Rock Engineering》1982,15(2):99-110

SummaryRock Bursting Phenomena in a Superficial Rock Mass in Southern Central Sweden Rock bursting phenomena have been observed in connection with excavation of two shallow sited rock tunnels in the Forsmark area in southern, central Sweden. The tunnels are excavated in gneiss granite and the rock cover varies between 5–15 m. The stress release occurred locally in the tunnels which indicates significant variations in rock stresses.In situ measurements of the triaxial stress situation carried out in the area show values of the principal stresses in the horizontal plane of a magnitude in excess of 20 MPa in the superficial rock mass. The rock stress measurements indicate a clear correspondence of the directions of the highest compressive stress and the rock foliation. There is also a clear correspondence between the directions of a vertical and a horizontal joint set and the highest compressive stress. The three-dimensional stress tensor indicates that the horizontal fractures are exposed to the smallest closure pressure, i. e. the vertical stress, which set should therefore be most open. The horizontal joint set in the superficial rock mass has a significantly higher value of aperture than the vertical sets which may be a consequence of the stress situation in the rock mass. The rock bursting is not attributed to a breakage of the rock matrix, but merely to a propagation of already existing small fractures and potential fractures. The stress situation in the Forsmark area may be regarded as an uniaxial stress field in the horizontal plane.With 12 Figures  相似文献   

β-FeOOH · Cl_n (akaganéite) and Fe_1-xO (wüstite) in hot brine from the Atlantis II Deep (Red Sea) and the uptake of amino acids by synthetic β-FeOOH · Cl_n     

Nils G Holm  Michael J Dowler  Tommy Wadsten  Gustaf Arrhenius 《Geochimica et cosmochimica acta》1983,47(8):1465-1470

A yellowish brown precipitate in samples of Red Sea hot brine has been identified as β-FeOOH · Cl_n (akaganéite) by Guinier-Hägg X-ray diffraction techniques, transmission electron microscopy (TEM), electron diffraction and electron excited X-ray fluorescence. Microcrystals of Fe_1-xO (wüstite) were also identified by electron diffraction. Synthetic β-FeOOH · Cl_n characterized by the same techniques was identical with the brine precipitate.Bonding between β-FeOOH · Cl_n and ¹⁴C labeled amino acids is pH dependent: between pH 3 and pH 7.6 amino acids were bound to the extent of 40 to 60% or 0.6 to 0.9 mmol per kg of iron oxide hydroxide. Some selectivity in affinity for different amino acids was observed, however, the effect is insufficient to explain the unusual distribution in the Atlantis II Deep brine reported in the literature.  相似文献   

Mineralogy of granulated wood ash from a heating plant in Kalmar, Sweden   总被引：3，自引：0，他引：3  

Sirkku L. Holmberg  Tommy Claesson 《Environmental Geology》2001,40(7):820-828

The central heating plant of Kalmar, Sweden produces 200-300 tons wood ash every year. A stabilised material for nutrient recycling is produced by adding water and dolomite to the wood ash and granulating the mixture. Combined mineralogy and chemistry can be used to interpret the transformation processes that occur during hardening and weathering of the granules, thus leading to a possibility to refine the production process and final characteristics of the granules. Mineralogy was separately studied in the wood ash, dolomite, self-hardened wood ash and granules by X-ray diffraction. Magnesium- and calcium-containing minerals are most common in the ash materials in the present study. The amounts of portlandite and calcite present in self-hardened and granulated ash samples are clearly higher than those in the untreated ash, showing that these minerals are formed during the treatments. Additionally, one potassium-containing secondary mineral, syngenite, is formed during the self-hardening of wood ash. Quartz, dolomite and the Fe-K-Mg-silicate in the granules originate from dolomite. The secondary minerals gypsum and calcium silicate hydrate are present in the granules. Portlandite occurs only in control granules in the field study. This suggests that hardening of granules continues in the field and portlandite is transformed into calcite. After up to 3 years on forest soil, the crystalline compounds dolomite, calcite, quartz, ankerite, albite and alumohydrocalcite are present in granules, of which alumohydrocalcite is formed as a secondary mineral in the field. These results suggest that the dissolution of granulated wood ash is strongly delayed compared with untreated wood ash and self-hardened wood ash because of the formation of less soluble compounds during the granulation process.  相似文献   

A deeper look at the colors of the saturnian irregular satellites     

Tommy Grav  James Bauer 《Icarus》2007,191(1):267-285

We have performed broadband color photometry of the twelve brightest irregular satellites of Saturn with the goal of understanding their surface composition, as well as their physical relationship. We find that the satellites have a wide variety of different surface colors, from the negative spectral slopes of the two retrograde satellites S IX Phoebe (S^′=−2.5±0.4) and S XXV Mundilfari (S^′=−5.0±1.9) to the fairly red slope of S XXII Ijiraq (S^′=19.5±0.9). We further find that there exist a correlation between dynamical families and spectral slope, with the prograde clusters, the Gallic and Inuit, showing tight clustering in colors among most of their members. The retrograde objects are dynamically and physically more dispersed, but some internal structure is apparent.  相似文献   

Environmental Effects in Galaxies: Molecular Gas and Nuclear Activity     

Duilia de Mello  Tommy Wiklind  Marcio A.G. Maia 《Astrophysics and Space Science》2001,276(1):67-80

Galactic X-ray emitters have been described by Giovannelli andSabau-Graziati (1993). We would address the bulk of this paper on HighMass X-Ray Binaries (HMXBs) and particularly in demonstrating theimportance of these systems as powerful laboratories to test the propertiesof high-energy physical processes through the multi-frequency studies oftheir behavior. Interactions between the two components of those systemsoriginate processes that manifest themselves along a large part of theelectromagnetic spectrum. Therefore it is possible to study indirectlyhigh-energy phenomena through the analysis oflow-energy phenomena with enormous advantages since the latter can bemainly studied via ground-based experiments, meanwhile the former can bestudied only by mean of space-based experiments, at least up to energiesof order 100 GeV.Moreover, since HMXBs are galactic, their emissions are the highestmeasurable; this renders such systems the most powerful laboratories to testtheories on collapsed objects, which can be scaled to extra-galactic distancesand dimensions. This fact suggests that HMXBs can be in general useful targetseven for small satellites, and in particular, in the X-ray energy range,very suitable targets for experiments like SIXE (Spanish Italian X-rayExperiment) to be launched in small satellites such as the Spanish MINISAT-02.  相似文献   

Impacts of Methane on Carbon Dioxide Storage in Brine Formations          下载免费PDF全文

Mohamad R. Soltanian  Mohammad A. Amooie  David R. Cole  Thomas H. Darrah  David E. Graham  Susan M. Pfiffner  Tommy J. Phelps  Joachim Moortgat 《Ground water》2018,56(2):176-186

In the context of geological carbon sequestration (GCS), carbon dioxide (CO₂) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH₄). In this multicomponent multiphase displacement process, CO₂ competes with CH₄ in terms of dissolution, and CH₄ tends to exsolve from the aqueous into a gaseous phase. Because CH₄ has a lower viscosity than injected CO₂, CH₄ is swept up into a ‘bank’ of CH₄‐rich gas ahead of the CO₂ displacement front. On the one hand, this may provide a useful tracer signal of an approaching CO₂ front. On the other hand, the emergence of gaseous CH₄ is undesirable because it poses a leakage risk of a far more potent greenhouse gas than CO₂ if the cap rock is compromised. Open fractures or faults and wells could result in CH₄ contamination of overlying groundwater aquifers as well as surface emissions. We investigate this process through detailed numerical simulations for a large‐scale GCS pilot project (near Cranfield, Mississippi) for which a rich set of field data is available. An accurate cubic‐plus‐association equation‐of‐state is used to describe the non‐linear phase behavior of multiphase brine‐CH₄‐CO₂ mixtures, and breakthrough curves in two observation wells are used to constrain transport processes. Both field data and simulations indeed show the development of an extensive plume of CH₄‐rich (up to 90 mol%) gas as a consequence of CO₂ injection, with important implications for the risk assessment of future GCS projects.  相似文献   

Potential environmental issues of CO₂ storage in deep saline aquifers: Geochemical results from the Frio-I Brine Pilot test,Texas, USA     

Yousif K. Kharaka  James J. Thordsen  Susan D. Hovorka  H. Seay Nance  David R. Cole  Tommy J. Phelps  Kevin G. Knauss 《Applied Geochemistry》2009

Sedimentary basins in general, and deep saline aquifers in particular, are being investigated as possible repositories for large volumes of anthropogenic CO₂ that must be sequestered to mitigate global warming and related climate changes. To investigate the potential for the long-term storage of CO₂ in such aquifers, 1600 t of CO₂ were injected at 1500 m depth into a 24-m-thick “C” sandstone unit of the Frio Formation, a regional aquifer in the US Gulf Coast. Fluid samples obtained before CO₂ injection from the injection well and an observation well 30 m updip showed a Na–Ca–Cl type brine with ∼93,000 mg/L TDS at saturation with CH₄ at reservoir conditions; gas analyses showed that CH₄ comprised ∼95% of dissolved gas, but CO₂ was low at 0.3%. Following CO₂ breakthrough, 51 h after injection, samples showed sharp drops in pH (6.5–5.7), pronounced increases in alkalinity (100–3000 mg/L as HCO₃) and in Fe (30–1100 mg/L), a slug of very high DOC values, and significant shifts in the isotopic compositions of H₂O, DIC, and CH₄. These data, coupled with geochemical modeling, indicate corrosion of pipe and well casing as well as rapid dissolution of minerals, especially calcite and iron oxyhydroxides, both caused by lowered pH (initially ∼3.0 at subsurface conditions) of the brine in contact with supercritical CO₂.  相似文献