Notes: An underground gravity study was carried out under extreme conditions of the Alpine regions. The lead–zinc mine Bleiberg, Carinthia, was selected as an example to show the possibilities and limitations of the subsurface gravity method. For in situ density determinations, gravity measurements were made in two vertical mine shafts passing through Triassic sedimentary rocks of the Bleiberg Unit. The main prblem in gravity data reduction in extremely rugged topography is the accurate calculation of the terrain effect on underground stations. A general discussion of the various corrections required for the gravity measurements in the mine is presented. The mean interval densities in the two shafts, in limestone, dolomite, and schists formations, were determined as 2.76 and 2.77 g/cm3, respectively, with an accuracy of better than 0.01 g/cm3 for a depth interval of 50 m. The interval densities provide valuable information about the lithological and structural changes in the shaft surroundings and also agree well with the representative hand sample densities.In the second part, the applications of subsurface horizontal gravity surveys in exploration are discussed. Since the influence of topography is less underground because of the greater distance to the surface, subsurface surveys have definite advantages over surface surveys and can be very helpful in locating anomalous density zones in the mines. An example of gravity survey with a station spacing of 10 m at a depth of about 540 m is presented.

Notes: Effective management of a ground-water system requires description and prediction of the transport and fate of contaminants in that system. This can be facilitated by using mathematical models which accurately represent the physical phenomena operative in the system. One of the most significant phenomena impacting the transport of many organic pollutants is partitioning between the solid (soil) and aqueous (ground-water) phases.The tendency of a contaminant to partition may be roughly approximated from measurements of such constitutive properties as the octanol: water partition coefficient of the contaminant and organic carbon content of the soil. Such rough approximations provide a basis for cursory appraisal, but are inadequate for quantitative system descriptions, particularly where nonlinear equilibrium sorption, kinetically dependent partitioning, or irreversible and/or hysteretic phase distribution phenomena are operative. Accurate simulation of solute transport frequently requires the incorporation of kinetic parameters and/or a nonlinear isotherm relationship to define transport phenomena in the fundamental equations governing mass transport. Laboratory measurements may be utilized to assess sorptive factors of importance, kinetic properties of an organic solute and a soil system, and equilibrium partitioning relationships. Such measurements can be utilized to provide more accurate modeling of contaminant transport.

Notes: The step-drawdown test is frequently utilized by hydrogeologists as an aid in assessing well efficiency and approximate pumping capacity. Unfortunately, the analysis of step-drawdown data presently requires either a solution to a system of highly nonlinear equations or the application of tenuous assumptions relative to the solution form. A method for solution is derived which does not require limiting assumptions, type-curve methods or extensive computer facilities.

Notes: Traveltime and amplitude residuals of P waves from teleseismic events show a positive correlation at the stations of the German seismic broad-band array GRF. Fast arrivals consistently have reduced amplitudes in the four frequency ranges considered (short-period bandpass, WWSSN-SP filter, broad-band velocity and WWSSN-LP filter).With the exception of the WWSSN-LP filter, 40–60 per cent of the average of the relative traveltime and almost 100 per cent of the average of the amplitude residuals at individual stations, with respect to the reference station A1, can be explained by near-surface sediment layers. These shallow structures are known from local and regional geology and are documented in borehole, local refraction and polarization studies. This aximuthal- and distance-independent term (station average) reaches values of up to -0.55 s and -0.15 units in log amplitude (magnitude).Even after the removal of these station averages, which also contain a trend of increasing crustal and uppermost mantle velocity from north to south, large azimuthal- and distance-dependent relative traveltime and magnitude residuals can be observed across the array. These residuals vary between -0.8 and +1.1 s and -0.54 and +0.72 magnitude units. Negative (fast) traveltime residuals are again related to negative magnitude residuals (small amplitudes). The azimuthal- and distance-dependent patterns of these residuals are identical within three distinct clusters of stations. The main features of the residual patterns correlate well with the main fault systems and inhomogeneities near the array, some of which have been postulated previously. The velocity anomalies causing the azimuthal- and distance-dependent residuals are located in crust and uppermost mantle under the array and its vicinity.The fact that local effects like sedimentary covers are responsible for 40 per cent or more of the station average residuals demonstrates again that site effects should be removed before tomographic methods are employed. The simple stations corrections usually applied in global tomography might severely underestimate the influence of local and regional velocity anomalies, since even after the removal of the station average residual large azimuthal- and distance-dependent traveltime and amplitude anomalies remain between stations less than 100 km apart. These anomalies due to shallow inhomogeneities might then erroneously be mapped into features at greater depth.

Notes: The GRF array is situated on Jurassic limestone of the Franconian Alb in SE Germany. The mislocation vectors show symmetry axes in their slowness and azimuth components. For the slowness the line of separation is at about 95d̀ against north. The azimuth pattern shows a symmetry axis nearly perpendicular to the axis in the slowness pattern. Waves arriving from NE have a reduced slowness, whereas waves from SW have a larger slowness. The largest azimuth anomalies are found in the directions where the slowness components change direction. These effects can to a large extent be modelled by a low-velocity sedimentary layer dipping to NNE with about 0.8d̀ dip. Such a sedimentary wedge correlates well with the geological data, is able to reproduce the observed mislocation vector pattern and explains a major part of the observed traveltime residuals. It furthermore demonstrates that local effects, like the influence of sedimentary covers, should be removed before inversion procedures and tomographic methods are applied.

Notes: The aim of this study is to demonstrate what effects subduction zones, i.e. laterally inhomogeneous, high-velocity anomalies in the Earth's mantle, can have on the traveltimes and the amplitudes of teleseismic recordings, and to show that the amplitude anomalies are large enough that they can be used in the determination of the structure of subducting slabs.The method used for the computation of the seismograms in these laterally inhomogeneous media is the Gaussian beam method which, in contrast to the ray method usually used, gives correct amplitudes at caustics and in critical regions. The restriction to 2-D models in the downdip direction of the slab, i.e. the assumption that there is no change along strike of the subduction zone, reduces the number of free parameters. For the short-period waves considered here it is sufficient that the section of the slab be uniform along strike for a few hundreds of kilometres. This geometry is satisfied by many subduction zones. Furthermore we expect pronounced effects of the subduction zones to be in the downdip direction because the wave will then sample the anomaly to a large extent. The influence of the following parameters of the slab on teleseismically recorded traveltimes and amplitudes is studied in detail: maximum velocity anomaly, depth of penetration, thickness of the slab and dip change. The influence of the source location, i.e. depth and epicentre, is also considered.We compare seismograms from this modelling to those computed from a radially symmetric reference earth and observe the following effects: negative traveltime residuals, occurrence of caustics and focusing h2reasing the magnitude by up to +0.7 magnitude units, defocusing and the creation of shadow zones. Receiver regions with large amplitude anomalies are not necessarily regions where large traveltime anomalies occur. Regions with little change in their traveltime anomalies can show dramatic changes in amplitude (larger than Δmb=± 1). Small structures of subduction zones are better resolved by amplitude information than by traveltime information. A combined interpretation of traveltimes and amplitudes yields much better resolution of the structure of subduction zones because traveltimes and amplitudes contain independent information about the structure studied. This helps to eliminate ambiguities which may not be resolved when using only one type of information (traveltimes or amplitudes) especially in aseismic parts of slabs where no additional information from seismicity is available.Observations of amplitudes for deep Kurile events recorded at European stations show anomalies that can be explained by a slab with a penetration depth of 670 km, thus indicating the usefulness of this approach in the determination of subduction zone structure.

Notes: Seismic P waves from a total of about 200 nuclear explosions in the USA, the former USSR and China, observed at 10 arrays and four networks in Europe, Canada and the USA, are used to analyse the structure at the base of the mantle and the core-mantle boundary (CMB).The simple waveforms and well-controlled source parameters of nuclear explosions allow one to use the events as source arrays in addition to the usual receiver array configuration. A new array technique (double beamforming; Krüger et al. 1993) integrating both concepts is applied, which increases the slowness resolution considerably.A total of 56 source-receiver combinations (i.e. reflection points in the lower mantle or on the CMB) could be analysed. In five regions, anomalous arrivals (PdP) with slowness and arrival times between those of P and PcP are observed. One of these five areas (Svalbard region) shows short-period PcP/P amplitude ratios, which are about three times higher than those predicted by standard earth models. In the Severnaya Zemlya region, where PdP and PcP precursors were observed previously (Krüger et al. 1993), PcP shows azimuth deviations of up to 10°. For some other regions, deviations of the PcP waveform from the direct P waveform are also observed.These anomalous phases and the PcP waveform distortions cannot be explained with standard 1-D earth models. They are probably produced by inhomogeneities in the lowermost mantle. The observed variations in the waveforms are strong indications of a laterally heterogeneous structure in two depth ranges. The first is the CMB and its immediate vicinity of a few tens of kilometres; the second region is the depth range between about 200 and 300 km above the CMB. Maps of the North Pole region, giving the distributions of inhomogeneities in the lower mantle and on the CMB, are presented. These maps show evidence of strong heterogeneity of the D″ boundary layer and possibly also of the CMB in the same area.