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No description available.

No description available.

No description available.

No description available.

No description available.

The Krafla volcanic system is a spreading segment in north Iceland. A decade-long crustal spreading episode began there in 1975. Up to 8 m of rift-normal surface widening occurred along an 80-90 km-long section of the plate boundary. Isostatic uplift in the vicinity of the melting icecap Vatnajōkull has been proposed. A third GPS survey of a regional network surrounding the Krafla system was conducted in 1992. In 1991 a 10-point GPS network was installed and measured for the first time around Vatnajōkull. The 1991 and 1992 GPS data were processed using the Bernese software. Differencing the 1992 results with those from 1987 and 1990 revealed a regional deformation field with a maximum, rift-normal expansion rate of 4.4 cm/yr near the rift, decreasing to 3 cm/yr at large distances. The time-averaged spreading rate in north Iceland, 1.8 cm/yr, cannot account for this deformation. The vertical deformation field reveals regional uplift throughout the network area, at its maximum closest to the rift and decreasing with distance. Three different models were applied to study the postdyking ground deformation, (1) continued opening at depth on the dyke plane in an elastic halfspace, (2) stress redistribution in an elastic-viscous layered medium, and (3) stress redistribution in an elastic layer over a viscoelastic halfspace. The latter model was developed by extending mathematical techniques previously used to model surface displacements resulting from thrust faulting to the case of dyke emplacement. For the model of continuous dyking at depth, a range of dykes will fit the deformation field. Using the elastic-viscous model, the motion 1987-1990 and 1990-1992 is simulated adequately given the survey errors, but the 1987-1992 deformation is poorly fitted, suggesting that a more realistic geophysical model is required. Using the elastic-viscoelastic approach the effects of historical episodes in the region were subtracted from the observed displacement fields and the remaining motion was modelled as relaxation following the recent Krafla rifting episode. The best-fit model involves a halfspace viscosity of 1.1 x 10(^18) Pa s. The vertical field is noisy, but indicates that the Krafla dyke complex rifted the entire elastic layer. Isostatic uplift centred on Vatnajőkull is inconsistent with the vertical deformation field. The model suggests that the Krafla volcano became inactive after 1988/1989. The model further predicts that the width of the "plate boundary zone" is greater than that of Iceland itself.

Relatively few studies have been carried out on polymers at high rates of deformation compared to more traditional materials such as metals, and it is therefore important to develop constitutive models to help predict how materials will behave under specified conditions. The stress-strain behaviour of polymers shows a very marked dependence on time (or rate) and temperature. Polymers (including polyethylene, polypropylene, nylon 66, polyetherketone, polyetheretherketone, a liquid crystal polymer, polyethersulphone and polycarbonate) have been compressed at strain rates of -10-3 to 1O-1s-1 (using an "Instron" which measures deformation versus time at constant rates of compression) and _103s-1 (using a novel drop-weight impact machine) to strains of up to -100%. This drop-weight system is different from commercially available machines in that it operates in compression rather than fracturing specimens and provides stress-strain data directly. The initial crystallinity and orientation of specimens were examined using x-ray diffraction, and kinetic decomposition parameters were obtained using differential scanning calorimetry. Also thermocouples were inserted into some specimens compressed at high strain rates in order to measure any rises in temperature. Several important results have emerged so far: I) sufficiently high bulk temperature rises occ;ur during high rate deformation to considerably alter the stress-strain curve from isothermal conditions; 2) localised deformation in the form of cracking or shear banding in tough polymers appears to lead to temperature rises sufficiently high for significant thermal decomposition to occur; 3) data obtained at lower rates could be approximately fitted to the Eyring Theory unlike that obtained at the highest rate; 4) initial investigations suggest that Poisson's ratio varies with strain and strain rate and is not a constant of 0.5 as generally assumed.

The Eastern Alps are a belt of major deformation formed by the convergence and collision of Europe with the Adriatic microcontinent. A major tectonic boundary can be defined between the dominantly continental Austroalpine domain, which represents the northerly fringe of Adria; and the Pennine oceanic domain, which once lay between the Austroalpine domain and Europe. This boundary is one of the key areas for unravelling the convergent tectonic history of the Eastern Alps. The main emphasis of this thesis is on the deformational behaviour of the Austroalpine domain and its implications for the regional tectonic processes that were instrumental in forming the structure of the Eastern Alps. The data for this work are derived from structural and metamorphic studies in the S.E. Tauern in profiles straddling the boundary, and a review of the published regional geology. The first manifestation of convergence is the development of a broad zone of thickened crust, including both Pennine and Austroalpine units, which underwent Cretaceous burial metamorphism. Postdating this thermal event in the Austroalpine domain, there was a further phase of regional deformation, which caused substantial reduction in the structural thickness. To the south of the Tauern Window, a study of the associated kinematic development gives a minimum estimate of 10km for this thinning, which radiometric dating suggests took place while convergence was still active. A comparable 10km post-metamorphic thinning is suggested throughout the Austroalpine domain in the Eastern Alps by the shortfall in the overburden compared to the depth of burial indicated by the Cretaceous metamorphic conditions. Major extension in a dominantly convergent tectonic setting cannot be accounted for by the paradigm of plate tectonics and implies that body forces acting on the thickened crust of the destructive margin were a major driving force for deformation.

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