The mud volcanoes of Pakistan

Marine-geologic investigations on the Arabian Sea by Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) in 1995 and 1998, and land expeditions in 1998 and 1999 to the coastal regions of the Makran Desert/Pakistan have extended the knowledge of the aerial distribution of mud volcanoes. These structures rise from under-compacted formations within the regional accretionary prism, which is built by the subduction of the oceanic crust of the Arabian Sea and its km-thick sedimentary load. The occurrence of mud volcanoes is limited to the abyssal plain near the accretionary front, to the coastal region of the Makran Desert and to a region in the interior of the Desert to the south to southeast of the so-called Hinglay Synform. The location of mud volcanoes in Pakistan is clearly tied to fault systems. Mud volcanoes are conspicuously absent on the lower slope of the accretionary prism, where thick gas hydrate layers have developed. The presence of large gas plumes emerging from the seafloor landward of the gas hydrate stability zone at water depths of less than 800 m points to a redirection of fluids from depth, which might explain the absence of mud volcanoes along the lower slope.     

Granulometric and chemical composition of the Sava River sediments upstream and downstream of the Krsko nuclear power plant

Total concentrations of 13 elements (K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Rb, Sr, Y, Zr, Pb) in the size-fractionated Sava River sediments upstream and downstream of the Krsko nuclear power plant together with metal speciation within bulk sediment have been investigated. Trace metals generally increase with decreasing particle size, however, because of entrapment of organic matter in the 0.63–1 mm fraction, concentrations in the coarser sediment fraction are higher than expected. Exchangeable Pb, Zn, Cu, Mn, Cr and Fe are generally found to represent a negligible fraction of the total metal concentration of the bulk sediment. Seasonal variations of the Pb, Zn and Cu concentrations in the <0.5 mm fraction reflect decreased values during the spring period. Heavy metal concentrations in the 2003 waste water discharges from the Krsko nuclear power plant released into the Sava River were much lower than their maximum allowed values. Combined rubidium and organic matter normalization of the Zn, Pb and Cu concentrations, which was applied on the minus 0.063 mm fraction, indicated three potential sources of contaminants.     

Geochemical characteristics of the slip zones of a landslide in granitic saprolite,Hong Kong: implications for their development and microenvironments

Geochemical investigations of the slip zones of a landslide in granitic saprolite revealed that they have signatures distinct from their host materials. These distinctions include stronger Si depletion, higher Al enrichment, greater LOI, significant fixations of Mn, Ba and Ce, stronger negative Eu anomalies, and greater accumulations of other rare earth elements (REE). Altogether, these geochemical characteristics indicate that: (a) the slip zones have greater abundance of clays, consistent with field and microscopic observations; (b) concentration of clay size particles within the slip zones may have been from downward leaching and deposition, and lateral transportation of Al-Si solutions and colloids through pores and fractures within the saprolite; and (c) there were prevailing oxidation and poor drainage, and occasional reduction conditions within the slip zones. It was concluded that geochemical analyses could be effective in gathering clues for understanding the development and nature of slip zones in landslide investigations.     

Barium anomaly in the Cambrian-Vendian aquifer system in North Estonia

A barium anomaly with a maximum Ba²⁺ concentration of 6.37 mg/l was distinguished in a Cambrian-Vendian (Cm-V) aquifer system that is widely used as a drinking water source in the towns Kunda, Rakvere and Kohtla-Järve of North-Estonia. The modelling results show that at low sulphate concentrations (below 3 mg/l) Ba²⁺ contents can exceed the limit values for drinking water (such as 2 mg/l set by US EPA). Bicarbonate ions in their common concentration range in groundwater cannot limit Ba²⁺ at its content below 10 mg/l. The probable natural sources of the anomaly are the crystalline basement and its weathering zone. Groundwater in the clayey weathering core is hydraulically connected with the overlying Cm-V aquifer system, thus the upconing of deeper-seated groundwater, caused by intensive exploitation of wells, is possible.     

Effects of iron black varnish on petrophysical properties of building sandstone

In zones washed by rain (façades, pinnacles, pilasters), fine siliceous sandstones are covered by a black varnish, which gives a dirty appearance to monuments. In composition, structure and areas covered by it, it differs from the usual black gypsum crust. Experiments carried out on blocks covered by black varnish show the modifications due to their growth. Results show that despite their low thickness and the coherence of the stone below, the accumulation of hydrophobic matters and the wetting-drying cycles modify the transfer properties of sandstones several centimeters below the surface. Thus, although sandstones seem to be protected by the black varnish, in the long run, a flake detachment process, in the areas covered by it, affects them. Therefore, damage to sandstones by black varnish can be explained by the fact that a wetting and drying cycle modifies the pore network.     

Composition and assemblage characteristics of magnetic minerals in layer S<Subscript>5-1</Subscript> of Xifeng and Duanjiapo sections

Relatively strongly magnetic fine components (< 30μm, XS-4J and DS-4J) which are most environmentally sensitive were separated from layer S_5-1 in the Xifeng and Duanjiapo loess sections and analyzed by MPV-3 for their morphometric characteristics and reflectance, SEM-ESD for their element contents and XRD for their mineral phases, respectively. The results showed that minerals in both samples are dominated by detrial Fe-Ti oxides of aeolian origin. In sample XS-4J the reflectance and iron contents of magnetic minerals are usually high. In addition to magnetite (Fe₃O₄), maghemite (γFe₂O₃) and hematite (Fe₂O₃), some Fe-high oxide (72.25 wt%–86.67 wt%), ilmenite (FeTiO₃), and magnetite-ulvöspinel [Fe(FeCr)O₄, Fe (FeNi)O₄] were also detected. In sample DS-4J obvious negative linear correlations were found between Ti and Fe, and the contents of Mn, Si, Al and Ca are usually high and the minerals are dominated by magnetite (maghemite), goethite (FeOOH) and limonite (containing Si and OH). In addition, the signs of corrosion of magnetic minerals and newly crystallized magnetite (maghemite) were recognized. Differences in the composition and assemblage characteristics of magnetite minerals between XS and DS reflect significant differences in source rocks and preserving conditions.     

Ellipsoidal geoid computation

Modern geoid computation uses a global gravity model, such as EGM96, as a third component in a remove–restore process. The classical approach uses only two: the reference ellipsoid and a geometrical model representing the topography. The rationale for all three components is reviewed, drawing attention to the much smaller precision now needed when transforming residual gravity anomalies. It is shown that all ellipsoidal effects needed for geoid computation with millimetric accuracy are automatically included provided that the free air anomaly and geoid are calculated correctly from the global model. Both must be consistent with an ellipsoidal Earth and with the treatment of observed gravity data. Further ellipsoidal corrections are then negligible. Precise formulae are developed for the geoid height and the free air anomaly using a global gravity model, given as spherical harmonic coefficients. Although only linear in the anomalous potential, these formulae are otherwise exact for an ellipsoidal reference Earth—they involve closed analytical functions of the eccentricity (and the Earths spin rate), rather than a truncated power series in e². They are evaluated using EGM96 and give ellipsoidal corrections to the conventional free air anomaly ranging from –0.84 to +1.14 mGal, both extremes occurring in Tibet. The geoid error corresponding to these differences is dominated by longer wavelengths, so extrema occur elsewhere, rising to +766 mm south of India and falling to –594 mm over New Guinea. At short wavelengths, the difference between ellipsoidal corrections based only on EGM96 and those derived from detailed local gravity data for the North Sea geoid GEONZ97 has a standard deviation of only 3.3 mm. However, the long-wavelength components missed by the local computation reach 300 mm and have a significant slope. In Australia, for example, such a slope would amount to a 600-mm rise from Perth to Cairns.     

Surface gravitational field and topography changes induced by the Earth’s fluid core motions

Using a Love number formalism, the elastic deformations of the mantle and the mass redistribution gravitational potential within the Earth induced by the fluid pressure acting at the core–mantle boundary (CMB) are computed. This pressure field changes at a decadal time scale and may be estimated from observations of the surface magnetic field and its secular variation. First, using a spherical harmonic expansion, the poloidal and toroidal part of the fluid velocity field at the CMB for the last 40 years is computed, under the hypothesis of tangential geostrophy. Then the associated geostrophic pressure, whose order of magnitude is about 1000 Pa, is computed. The surface topography induced by this pressure field is computed using Love numbers, and is a few millimetres. The mass redistribution gravitational potential induced by these deformations and, in particular, the zonal components of the related surface gravitational potential perturbation (J₂, J₃ and J₄ coefficients), are calculated. Overall perturbations for the J₂ coefficient of about 10^–10, for J₃ of about 10^–11 and for J₄ are found of about 0.3×10^–11. Finally, these theoretical results are compared with recent observations of the decadal variation of J₂ from satellite laser ranging. Results concerning J₂ can be described as follows: first, they are one order of magnitude too small to explain the observed decadal variation of J₂ and, second, they show a significant linear trend over the last 40 years, whose rate of decrease amounts to 7% of the observed value.     

Surveying co-located space-geodetic instruments for ITRF computation

A new and comprehensive method is presented that can be used for estimating eccentricity vectors between global positioning system (GPS) antennas, doppler orbitography and radiopositioning integrated by satellites (DORIS) antennas, azimuth-elevation (AZ-EL) very long baseline interferometry (VLBI) telescopes, and satellite laser ranging (SLR) and lunar laser ranging (LLR) telescopes. The problem of reference point (RP) definition for these space-geodetic instruments is addressed and computed using terrestrial triangulation and electronic distance measurement (EDM) trilateration. The practical ground operations, the surveying approach and the terrestrial data processing are briefly illustrated, and the post-processing procedure is discussed. It is a geometrically based analytical approach that allows computation of RPs along with a rigorous statistical treatment of measurements. The tight connection between the geometrical model and the surveying procedure is emphasized. The computation of the eccentricity vector and the associated variance–covariance matrix between an AZ-EL VLBI telescope (with or without intersecting axes) and a GPS choke ring antenna is concentrated upon, since these are fundamental for computing the International Terrestrial Reference Frame (ITRF). An extension to RP computation and eccentricity vectors involving DORIS, SLR and LLR techniques is also presented. Numerical examples of the quality that can be reached using the authors approach are given. Working data sets were acquired in the years 2001 and 2002 at the radioastronomical observatory of Medicina (Italy), and have been used to estimate two VLBI-GPS eccentricity vectors and the corresponding SINEX files.