The 33rd International Geological Congress, Oslo 2008

The 33rd International Geological Congress is being organised jointly by the Nordic countries and to be held in Oslo, Norway, August 6-14th, 2008. This ＂Geoscience World Congress 2008＂ will run up to 40 parallel science sessions, poster sessions, an extensive exhibition, short-courses, workshops, and business meet- ings; about 50 exciting preand post-Congress excursions are planned. The excursions include all the Nordic countries, as well as Greenland, Svalbard, the Faeroes, Russia and Ukraine. All major geoscientific themes are being covered by the Congress which has been divided into two parts, Sunday lOth August being without Symposia and dedicated to workshops, short courses, business meetings and excursions. Through a series of ＂Themes of the Day＂, seven themes with major societal impact will be covered in plenary sessions with invited lecturers, including a key-note ＂StatoiIHydro lecture＂ given each day during the lunch interval. The venue is set up to offer a compact Congress with easy access to all sessions and other events. An extensive social and cultural programme is also being arranged.     

Exact synthetic seismograms for an inhomogeneity in a layered elastic half-space

Summary. The propagation of a pulsed elastic wave in the following geometry is considered. An elastic half-space has a surface layer of a different material and the layer furthermore contains a bounded 3-D inhomogeneity. The exciting source is an explosion, modelled as an isotropic pressure point source with Gaussian behaviour in time.
The time-harmonic problem is solved using the null field approach (the T matrix method), and a frequency integral then gives the time-domain response. The main tools of the null field approach are integral representations containing the free space Green's dyadic, expansions in plane and spherical vector wave functions, and transformations between plane and spherical vector wave functions. It should be noted that the null field approach gives the solution to the full elastodynamic equations with, in principle, an arbitrarily high accuracy. Thus no ray approximations or the like are used. The main numerical limitation is that only low and intermediate frequencies, in the sense that the diameter of the inhomogeneity can only be a few wavelengths, can be considered.
The numerical examples show synthetic seismograms consisting of data from 15 observation points at increasing distances from the source. The normal component of the velocity field is computed and the anomalous field due to the inhomogeneity is sometimes shown separately. The shape of the inhomogeneity, the location and depth of the source, and the material parameters are all varied to illustrate the relative importance of the various parameters. Several specific wave types can be identified in the seismograms: Rayleigh waves, direct and reflected P -waves, and head waves.     

Out‐of‐plane geometrical spreading in anisotropic media

Two-dimensional seismic processing is successful in media with little structural and velocity variation in the direction perpendicular to the plane defined by the acquisition direction and the vertical axis. If the subsurface is anisotropic, an additional limitation is that this plane is a plane of symmetry. Kinematic ray propagation can be considered as a two-dimensional process in this type of medium. However, two-dimensional processing in a true-amplitude sense requires out-of-plane amplitude corrections in addition to compensation for in-plane amplitude variation. We provide formulae for the out-of-plane geometrical spreading for P- and S-waves in transversely isotropic and orthorhombic media. These are extensions of well-known isotropic formulae.
For isotropic and transversely isotropic media, the ray propagation is independent of the azimuthal angle. The azimuthal direction is defined with respect to a possibly tilted axis of symmetry. The out-of-plane spreading correction can then be calculated by integrating quantities which describe in-plane kinematics along in-plane rays. If, in addition, the medium varies only along the vertical direction and has a vertical axis of symmetry, no ray tracing need be carried out. All quantities affecting the out-of-plane geometrical spreading can be derived from traveltime information available at the observation surface.
Orthorhombic media possess no rotational symmetry and the out-of-plane geometrical spreading includes parameters which, even in principle, are not invertible from in-plane experiments. The exact and approximate formulae derived for P- and S-waves are nevertheless useful for modelling purposes.     

Late glacial palaeoceanography of Hinlopen Strait, northern Svalbard

Timing and structure of the Late and post-glacial development of the northern Svalbard margin, together with the initial influx of Atlantic water into the Arctic Ocean are still very poorly constrained. We investigated a sediment core (NP94-51) from a high accumulation area on the continental shelf north of Hinlopen Strait with the purpose of resolving the timing and structure of the last deglaciation. Detailed analyses of ice-rafted detritus, benthic and planktonic foraminiferal fauna, diatom flora, grain size and radiocarbon dates are used to reconstruct the palaeoceanographic evolution of the area. Our results indicate that the disintegration of Hinlopen Strait ice and possibly the northern margin of the Svalbard Ice Sheet commenced between 13.7 and 13.9 ¹⁴C Ky BP. Influx of subsurface Atlantic waters into the area (12.6 ¹⁴C Ky BP) and the retreat of the sea ice cover, with the accompanying opening of the surface waters (10.8 ¹⁴C Ky BP), happened at different times and both much later than the disintegration of the ice sheets. The transition into the Holocene shows a two-step warming.     

Time-resolved spectroscopy of IR Gem at quiescence

We present some preliminary results of a spectroscopic study of the cataclysmic system IR Gem at quiescence during two orbital periods.The spectra covered the wavelength range 4000–7000 Å. The variations with the phase in the equivalent width of the H line confirms the existence of a maximum at phase 0.5.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Statistical Analysis of Well Logs Compared with the Geotechnical Data in Storegga Slide Area

Storegga Silide has been studied intensively due to the development of the big Ormen Lange gas field. Both marine and glacial deposits were involved in this slide, and marine layers were the sliding planes. Data from different wireline logs in the Storegga Slide area are analyzed using principal components and cluster statistical methods to characterize the two different kinds of sediments. The results show that the marine layer with high water content, high clay content and low strength can be differentiated from the glacial deposits. Moreover, the analysis from log response are compared with the physical parameters from the geotechnical boreholes, a good correlation exists in the dataset.     

Direct near-surface measurements of sensible heat fluxes in the Arctic tundra applying eddy covariance and laser scintillometry��the Arctic Turbulence Experiment 2006 on Svalbard (ARCTEX-2006)

Recent climate warming in the Arctic requires improvements in permafrost and carbon cycle monitoring, accomplished here by setting up long-term observation sites with high-quality in situ measurements of turbulent atmospheric energy fluxes applying the eddy covariance method and/or laser scintillometry in Arctic landscapes. Accurate quantification and well-adapted parameterizations of turbulent energy fluxes, e.g., during neutral to stable stratified conditions, are a fundamental problem in soil?Csnow?Cice?Cvegetation?Catmosphere interaction studies. We present results from the Arctic Turbulence Experiment (ARCTEX-2006) performed on the island of Svalbard, Norway, during the winter/spring transition 2006 that focus on data correction and quality assessment, on synoptic weather conditions, as well as site-specific micrometeorological features. A quality assessment and data correction adapted to the environmental conditions of polar regions demonstrates that specific measurement errors common at a high Arctic landscape could be minimized. We discuss the role of the intermittency of the turbulent atmospheric fluctuation of momentum and scalars, the existence of a disturbed vertical temperature profile (sharp inversion layer) close to the surface, and the relevance of possible free convection events for the snow or ice melt in the Arctic spring at Svalbard. Recommendations and improvements regarding the interpretation of eddy flux data as well as the arrangement of the instrumentation under polar distinct exchange conditions and (extreme) weather situations are presented.     

Heat transfer and the onset of chaos in a spherical,axisymmetric, anelastic model of whole mantle convection

Abstract

An isochemical uni-phase model of whole mantle convection has been developed in terms of which factors influencing the onset of time dependent chaotic behavior may be assessed. The model is spherical but restricted in generality to the analysis of axisymmetric solutions. In this paper we have employed it to examine the impact of compressibility and sphericity on the nature and onset of time dependence. Particular attention has been given to an examination of the impact that the onset of time dependence has upon the power law relation that connects the heat transfer (represented by the Nusselt number) to the strength of the thermal forcing (represented by the Rayleigh number). In order to obtain these results very extensive numerical simulations were required and the results themselves should be rather useful in the context of models of the thermal history of the planet.     

Preliminary Results on the 3-dimensional Seismic Structure of the Lithosphere under the USGS Central California Seismic Array

About 1500 readings of teleseismic P -time residuals obtained from the US Geological Survey seismograph network in central California have been used to obtain a three-dimensional image of seismic velocity anomalies for this area by the method of Aki, Christoffersson & Husebye We found that the California network is less suitable than the LASA and NORSAR arrays for this kind of studies because of its greater proportion of peripheral blocks in which the resolution is very poor for the stochastic inverse solution and the random error effect is severe for the generalized inverse solution. Nevertheless, the resultant velocity anomalies show a remarkable correlation with the San Andreas fault zone to a depth of 75 km. The anomaly pattern changes drastically as the depth exceeds 75 km, suggesting that the asthenosphere has been reached.