Shear wave refractions and wide-angle reflections recorded on densely spaced Ocean Bottom Seismometers (OBSs) in the Vøring have been modelled by use of 2-D kinematic ray-tracing. Twenty-five three component OBSs were deployed along a 120 km long profile, and the semi-regional shear-wave velocity model derived from modelling the horizontal components is compared with a regional model from 5 OBSs along the same profile. The overall shear-wave velocity distribution of the two models are fairly similar, proving that the regional procedure with large OBS spacing provides a reliable regional shear-wave velocity model. The semi-regional model is more detailed than the regional model due to the much closer receiver spacing. The vertical resolution is improved, especially in the shallow sediments, and this enables a more detailed lithological interpretation to be carried out. Intermediate and deep sediments are also better resolved in the semi-regional model, indicating both vertical and lateral changes in the lithology. The V_p/V_s ratio inferred for the crystalline basement is 1.75 in both models, considered to be typical for the continental crust. An increase in the V_p/V_s ratio in the lower crust is observed both in the regional and in the semi-regional model. This indicates a more mafic composition in the lower crust, supporting the interpretation that the lower crust is a “mixing” of continental crust and magmatic underplating.

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When determining the remanent magnetization (RM) of palaeomagnetic rock samples, it is assumed that the samples can be approximated by a magnetic dipole. This assumption greatly simplifies the inverse problem of determining the RM from the measured magnetic field of the sample. The magnetic field of the normally used cylindrical rock samples is however not identical to that of a dipole and care must be taken not to introduce any systematic errors. A numerical test of the effect of cylindrical sample shape on the determination of RM for a spinner-type magnetometer is presented. We find that for a spinner magnetometer the non-ideal sample shape has an insignificant effect (less than 0.3°error), for even the smallest possible sample-sensor distance. Comparing static and spinner-type magnetometers, it is clear that spinner-type magnetometers are less affected by the sample shape. Inhomogeneously magnetized samples are an obvious source of error when determining the RM. We numerically test the error in the determination of RM for the simple case of a laminated cylindrical sample with constant direction, but varying intensity of magnetization between the laminae. For strongly inhomogeneous samples we find an error of -4°for typical spinner-type magnetometer and -10°for static-type magnetometers.

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The pressure variations in the solar wind produce the oscillations in surface currents at the magnetopause boundary in order to nullify the pressure imbalance. These currents introduce compressional variations in the magnetic field within the magnetosphere. The response of transverse field line oscillations to such changes in the magnetic field has been brought out in perfectly reflecting ionospheric conditions. The analysis clearly shows that the fundamental toroidal modes are dominant in the dawn and the dusk sectors as revealed by the statistical studies of pulsations observed by the satellite AMPTE/CCE (Anderson et al., 1990). It is traditionally believed that such oscillations are mainly driven by Kelvin-Helmholtz (K-H) instability (Anderson et al., 1990). Our analysis shows that the dominance of fundamental toroidal modes in the dawn and dusk sectors can also be explained in terms of response to impressed pressure impulses without invoking K-H instability. The analysis also shows that poloidal modes do not exhibit any longitudinal structures. These results are consistent with the observations (Anderson et al., 1990).

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Fumarolic gases from the Kusatsu Shirane volcano, Japan were analyzed for the content and isotopic compositions of H₂O, the abundances and isotopic compositions of noble gas. The observed δ¹⁸O and ³⁶Ar/H₂O ratios could not be explained by an existing hydrothermal model in which a mixing between magmatic vapor (MAV) and meteoric water (ASW), a single-step separation to vapor and liquid phases and a subsequent partial H₂O vapor removal from the vapor phase have been considered. We constructed a revised model in which two-step mixingseparation and a subsequent partial H₂O vapor removal by condensation were considered. In the model, the first step was the mixing between MAV and ASW, and a subsequent separation to a primary vapor and liquid phases. In the secondary step, the primary vapor mixed with another fluid which has a δ¹⁸O lower than the primary vapor phase and a low ³⁶Ar/H₂O ratio relative to ASW. The mixture separates to secondary vapor and liquid phases. The fluid with low ³⁶Ar/H₂O ratio could be ASW partially vaporized in the geothermal area. The secondary vapor ascended and discharged as fumarolic gas. In the ascending process, the secondary vapor suffers a partial H2O vapor removal by condensation in various degrees.

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