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[en] Complete text of publication follows. Presently, both geophysical surveying and archaeological excavation requires precise determination of local coordinates and occasionally, the creation of a Digital Terrain Map. Besides topography implies essential information for archaeology in itself, combination of topography with geophysical data is able to give further knowledge about the archaeological objects. We carried out a high-resolution magnetic survey over the Roman-age ruins of the ancient town, Porolissum located in NW Romania. We surveyed an area of 100 m x 120 m with grid spacing of 0.5 m and we measured the total magnetic field and its vertical gradient. In this case study we present how joint application of magnetic and geodetic data can be used for topographic correction and interpretation of the magnetic anomaly map. Magnetic topographic correction is defined here as the removal of disturbing magnetic signals caused by the topography. In this procedure the induced magnetic field is calculated using the geomagnetic field of the Earth and the magnetic susceptibility of the soil. The induced magnetic field is subtracted from the measured data. We also investigate the magnitude of the induced field considering three different susceptibility values (0.0035, 0.005 and 0.01 SI) of the soil. In the correction the remanent magnetization of the soil is neglected. The correction was made for both the total field and the gradient. With the help of the topographic correction the obtained anomaly maps contain more details and they are easier to interpret. The corrected magnetic gradient map shows streets and foundations of houses like a present day city map. In some places two generations of houses built on top of each other's foundation can be recognized as the walls of different ages have different directions. The magnetic maps proved to be very useful in reconstructing the structure of the ancient city.
[en] Complete text of publication follows. Time-lapse magnetotellurics aims at studying resistivity variations in the earth due to internal processes, especially when aqueous or magmatic fluids are involved. Reliable estimates of the uncertainties of the MT parameters are essential to determine accurately the occurrence and timing of a subsurface event. These estimates depend mainly on magnetospheric activity. Chave and Thompson's (1989) estimation of errors is based on the internal dispersion of parameter estimates. We have run synthetic tests to assess whether the parameters and errors obtained by their approach (RRRMT software) are suitable for time-lapse studies. A measured ULF magnetic field is convolved with known impedance tensors to generate a synthetic electric field entirely correlated to the magnetic field. Both MT fields are then input into RRRMT. The resistivity estimates and their errors are then compared to the known values and we found significant differences between RRRMT and expected results. We have therefore designed a new and simple method to estimate errors in all dimensional cases. We present our results for both 1D and 3D cases, which leads to more realistic estimates than those obtained by RRRMT. Furthermore, we have initiated a study of the influence of magnetospheric ULF micropulsation activity on the measured error on impedance estimates, using synthetic data sets. Three methods are being considered: spectral electromagnetic energy, F. Plaschke's field-line resonance detector and an ad-hoc multifractal approach.
[en] Complete text of publication follows. The Southern African Magnetotelluric Experiment (SAMTEX) is imaging the electrical structures and geometries of the continental lithosphere below Botswana, Namibia and South Africa to depths of 200+ km. Primary geometrical information can readily be obtained from lithospheric-scale MT experiments about the three-dimensional variation in conductivity, and this information can be related to formation and deformation processes. In particular, one important piece of geometrical information easily and relatively precisely (to within 10%) obtained from MT data is the depth to the lithosphere-asthenosphere boundary (LAB), due to the sensitivity of conductivity to small fractions (<1%) of partial melt and/or increased water content. Over four phases of acquisition SAMTEX measurements have been made at a total of more than 700 MT sites in an area of greater than a million square kilometres, making it by far the largest-ever MT project undertaken. In particular, during Phase IV very challenging MT measurements were made in the highly-remote Central Kalahari Game Reserve, completing the coverage of Botswana. One of the most significant results from SAMTEX is the mapping of the LAB beneath the Archean cratons and bounding mobile belts of Southern Africa, particularly beneath Namibia and Botswana for which no prior lithospheric information exists. As would be expected, the electrically-defined LAB is generally shallow (150 km) beneath the mobile belts, deep (250 km) in the centres of the cratons, and transitional at the edges of cratons. Kimberlites are useful in also inferring lithospheric thickness, and diamondiferous kimberlites are located primarily where the electrical lithosphere is transitional in thickness, or where there is a change in its electrical anisotropy properties, both of which are craton edge effects. The electrical properties of the continental mantle derived from SAMTEX data can be compared with seismic ones derived from data from the South African Seismic Experiment (SASE) of the Kaapvaal Project and from regional/continental-scale investigations. Generally there is very good predictive linear agreement between seismic velocity and log(conductivity), indicative of both being influenced by the same bulk property factors, such as temperature, Mg and composition.
[en] Complete text of publication follows. Taylor states are magnetic field morphologies in a sphere or shell that obey Taylor's constraint, namely the vanishing of the azimuthal component of the Lorentz torque on every cylinder coaxial with the rotation axis of the Earth. We report on simple models of the internal magnetic field structure in a sphere and a spherical shell that are compatible with morphologies of the magnetic field at the core surface.
[en] Complete text of publication follows. The problem of thermal convective instabilities of a fluid in rotating self-gravitating spheres and shells has been subject of many papers mostly due to its importance for various geophysical and astrophysical applications including geodynamo problem. The fluid motion inside the Earth's outer core is examples of the flows for which knowledge on the general behaviour of such convection can be applied. In most of the works on this issue the Boussinesq fluid is considered. However, it is known that almost adiabatic states are typical for the deep convective interiors of all known planets and their moons. The asymptotic theory for the marginal stability of almost adiabatic geo-convection was given just recently by Starchenko et al. (2006). Asymptotic analysis was performed within the framework of local theory and new estimates of critical parameters differ from those obtained previously using the Boussinesq model. Here we consider the marginal stability of well-mixed almost adiabatic states in rapidly rotating spherical shells, whose inner to outer radius ratio does not exceed that of the modern Earth. The buoyancy source is the non-convective entropy gradient that is purely radial and consist of two terms - first one is linear in r and second one is r-2 proportional. This second term can be treated as normalized difference between temperatures or heat fluxes on the inner and outer boundaries of the core, and the stabilizing first term corresponds to the inner cooling of the core. The critical Rayleigh-type numbers, frequencies and solution structures of the marginal states are determined by both analytical and numerical methods. In each case we consider the range of convective layer widths and set of different values of Prandtl number.
[en] Complete text of publication follows. The influence of anisotropic diffusive coefficients on marginal stability of the horizontal fluid planar layer rotating about horizontal axis and permeated by a horizontal homogeneous magnetic field is studied. The linear stability analysis is performed using separable solution in the form of horizontal rolls. Both, stationary and overstable motions, are examined. Anisotropy of diffusive coefficients (thermal diffusivity and viscosity) is considered. Adopting the conclusions of Braginsky and Meytlis the turbulent diffusivities are enhanced in the x-direction of rotation, Ω=Ω0x and in the y-direction of the magnetic field, B=Bmy, in comparison with vertical z-direction. This anisotropy ( κxx = κyy > κzz, νxx = νyy > νzz), called BM anisotropy, is in this orientation of axis of rotation formally the same like oceanic type of stratification anisotropy (SA) considered in our former studies, because rotation and magnetic field are both in horizontal directions. In SA anisotropy due to density stratification determined by gravity, g=-gz, the diffusive coefficients have different values in z-direction and the ones in the horizontal directions, x and y (in oceanic (atmospheric) SA type anisotropy the horizontal diffusivities are greater (smaller) than vertical diffusivities). The influence of anisotropy on ΛE (Elsasser and Ekman numbers) regime diagram showing the regions of preference of oblique, cross and parallel steady rolls is studied. BM anisotropy decreases the domain of preferred oblique rolls (atmospheric SA anisotropy increases it) and impedes convection by decreasing critical Rayleigh number (atmospheric SA anisotropy enhances it). The influence of anisotropies on basic parameters describing overstable modes (wave numbers, frequency, angle between axis of rolls and basic magnetic field) is also studied. Study of importance of inertial terms shows, that these terms are relatively unimportant and can be neglected. In the case of inviscid overstable modes the Λq regime diagram is studied. Comparing the results from the case with vertical axis of rotation, there is significant difference, because the unique property of BM anisotropy (in the case of vertical axis of rotation the BM anisotropy handicapes the overstability by reducing the ranges of Elsasser number as well as Ekman number at which the overstability exists) is not present in the model with here studied horizontal axis of rotation.
[en] Complete text of publication follows. As the landslides constitute one of the main causes which may generate important damages, even catastrophic some times, we focused on the earthquake-induced landslide (Provita de Sus) to develop an appropriate methodology for assessing this type of geohazard. This paper highlights results of a first stage in the study of the interest area, consisting in a detailed electrical investigation and elaboration of a structural model, as well as of a second stage which is referring to the electric and electromagnetic multi-parametric monitoring, in order to find out a relevant connection between various geophysical parameters, also between geophysical parameters and some indicators of natural hazard, so that the premises of a near-real time geohazard assessment methodology get possible, even if it could be at the interface of more disciplines. This takes into account the fact that any algorithm is created for certain geological conditions, what confers credibility for a specific zone, with its own structural features at one time. Therefore, for the dangerous zones, related to the seismic activity, specific geomorphological conditions (steep slopes) and with climate changes (teeming rains), the monitoring of the slide motions, with an adequate sampling rate, represents a useful way to assure a near real-time geohazard assessment in order to avoid too high risks.
[en] Complete text of publication follows. The performance of the Hungarian National Radioactive Waste Repository programme for the final disposal of low- and intermediate-level radioactive waste started in 1993. Geophysical investigations on the site ongoing since 1997. Two magnetotelluric field campaigns were carried out in 2002 and 2005 along a 100 m grid with Stratagem EH-4 instrument. The frequency range was 10 Hz - 24 kHz (AMT). The geological setting of the area is paleozoic granite covered by quarter sediments (mainly loess). The topography of the investigated area is steep and diversified terrain. Bimodal 2D inversion was applied along 15 profiles perpendicular to valleys and ridges, constrained by the topography. A 3D resistivity distribution model was derived from the 2D inversion results. Two tunnels has been build until 2009, each tunnel is 2 km long. The MT measurements cover more than the half of the excavated region. The large amount of detailed geophysical, geological and hydrogeological information from the tunnel and the nearby drillings now can be compared to the 3D resistivity distribution model.
[en] Complete text of publication follows. Determining the conductivity of subsurface salty water layers containing Iodine using magnetotelluric (MT) method is our aim. The salty water layers specially if contain minerals such as Iodine have high electric conductivity. This study includes investigation down to 1300 m in the east of Alagol lake, located in the north of Golestan province, Iran. The area, a part of Kopeh-Dagh sedimentary basin, has been formed by last orogeny phase of Alpine and following erosion. Topographic reliefs of the area consist of loesses occurring naturally by temperature contrast between the Alborz and Turkmenistan desert. The area formation is Quaternary which consists of jammed sediments in the torrential holes. According to 1D and 2D models, three conductive layers were distinguished at depth of 20 m to 90 m, 110 m to 500 m and about 1100 m . The last two layers are interpreted as the layers which consist of salty water and probably Iodine constructions. Also resistive bodies are monitored in the 4th and 5th profiles that are appeared irregularly. Isolated conductive bodies are detectable at some sites in more depths. To prove the correctness of the results the 1D model of the MT data are compared with the results of a log record that is located at 4 Km southwestern of station B51. One final conclusion is confirmed a 200 m thick conductor at the depth of 700 m.
[en] Complete text of publication follows. Magnetovariational (MV) sounding results are commonly presented in the form of induction arrows (tippers). However, many examples show that horizontal magnetic inter-station (perturbation) responses look more informative and effective, especially in the tracing of elongated crustal and upper mantle conducting structures. These responses may extend capabilities of joint MT/MV inversion and their invariants can directly map conductivity anomalies. The only drawback is the requirement of simultaneous observations, thus conventional tipper data sets may be estimated from single station records and spatially denser. To this extent it is desirable to develop techniques capable to restore magnetic field components from tipper data arrays. These techniques exploit the potential representation of magnetic field in non-conducting atmosphere and conventionally apply spline approximation and Hilbert transform routines. In 2D this approach leads to direct integral equation solution (Vanyan, Varentsov, Sokolova), while in 3D it applies iterative schemes (Banks et al., Ritter) In this paper we describe two new implementations of such 3D iterative procedure (Kovacikova; Nowozynski, Jozwiak). Details of data interpolation and boundary conditions as well as iterative techniques are discussed. New procedures are used to calculate horizontal MV responses for tipper data sets of the EMTESZ-Pomerania sounding array. Also 2D calculations of this kind are performed along central profiles of this array. These calculations are compared with direct estimates of horizontal MV responses available at many sites of this array. The obtained results show that it is possible to reconstruct quite accurately horizontal MV responses from sufficiently dense tipper arrays. However, special attention is to be paid to peripheral tipper anomalies caused by geoelectric structures located outside of the recalculation grid. Also obvious is the need for the robust smoothing of tipper responses.