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Saragiotis C.,Eotvos Lorand Geophysical Institute | Scholtz P.,Eotvos Lorand Geophysical Institute | Bagaini C.,Schlumberger
Geophysical Prospecting | Year: 2010

For a linear elastic Earth the time derivative of the ground force is considered proportional to the far-field wavelet. Under the assumption that the baseplate is stiff and the bending forces of the baseplate are negligible, the ground force is also approximated by the sum of the accelerations of the baseplate and the reaction mass weighted by the respective masses. Combining these two assumptions, the time derivative of the weighted sum is considered proportional to the far-field wavelet. This result, often referred to as the far-field wavelet assumption, although convenient and most often employed is not always valid. We explore its validity using the spectral harmonic ratios of recorded data, which are used extensively in data filtering and analysis of vibratory data. We show that the far-field wavelet assumption fails particularly for harmonic components of even order. More compact soil after repeated shots further invalidates this assumption. Non-linear modelling of the ground under the vibrator point may provide a direction towards solving this discrepancy. Finally, we describe a method for the estimation of the harmonic spectral ratios. © 2009 European Association of Geoscientists & Engineers.

Hips K.,Hungarian Academy of Sciences | Haas J.,Hungarian Academy of Sciences | Vido M.,Eotvos Lorand Geophysical Institute | Barna Z.,Geological Institute of Hungary | And 3 more authors.
Sedimentology | Year: 2011

A peculiar facies of the Norian-Rhaetian Dachstein-type platform carbonates, which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments, occurs in the Zlatibor Mountains, Serbia. Microfacies investigations revealed that the blackened bioclasts are predominantly Solenoporaceae, with a finely crystalline, originally aragonite skeleton of fine cellular structure. Blackening of other bioclasts also occurs subordinately. Solenoporacean-dominated reefs, developed behind the platform margin patch-reef tract, were the main source of sand-sized detritus. The blackened and other non-blackened bioclasts are incorporated in automicrite cement. Radiaxial fibrous calcite cements in the dissolutional cavities are also black, dark grey or white. Reworked black pebbles were reported from many occurrences of peritidal deposits; in those cases, the blackening took place under pedogenic, meteoric diagenetic conditions. In contrast, in the inner platform deposits of the Ilidža Limestone, the blackening of bioclasts occurred in a marine-meteoric mixing-zone, as indicated by petrographic features and geochemical data of the skeleton-replacing calcite crystals. Attributes of mixing-zone pore waters were controlled by mixing corrosion, different solubility of carbonate minerals and microbial decomposition of organic matter. In the moderate-energy inner platform environment, large amounts of microbial organic tissue were accumulated and subsequently decomposed, triggering selective blackening in the course of early, shallow burial diagenesis. The δ18O and δ13C values of the mixing-zone precipitates and replacive calcite do not produce a linear mixing trend. Variation mainly resulted from microbial decomposition of organic matter that occurred under mixing-zone conditions. The paragenetic sequence implies cyclic diagenetic conditions that were determined by marine, meteoric and mixing-zone pore fluids. The diagenetic cycles were controlled by sea-level fluctuations of moderate amplitude under a semi-arid to semi-humid climate. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.

Dando B.D.E.,University of Leeds | Stuart G.W.,University of Leeds | Houseman G.A.,University of Leeds | Hegedus E.,Eotvos Lorand Geophysical Institute | And 2 more authors.
Geophysical Journal International | Year: 2011

Subducted slab roll-back, lithospheric instability and asthenospheric extrusion have all been proposed as mechanisms that explain the evolution of the extensional Pannonian Basin, within the convergent arc of the Alpine-Carpathian mountain system in central Europe. We determine the P- and S-wave velocity structure of the mantle to depths of 850km beneath this region using tomographic inversion of relative arrival-time residuals from 225 (P waves) and 124 (S waves) teleseismic earthquakes recorded by 56 stations of the Carpathian Basins Project (CBP) temporary seismic network (16-month duration) and 44 permanent seismic stations. The observed median P-wave relative arrival-time residuals vary between -1.13s (early) in the Alps and 1.12s (late) at the western end of the Carpathians; S-wave relative arrival-time residuals are about twice as large (-2.13s and 3.39s). We tested the effect of deterministic corrections on our relative arrival-time residuals using crustal velocity models from controlled source experiments, but show that the use of station terms in the inversion provides a robust method of correcting for near-surface crustal variation. Our tomographic models reduce the P-wave rms residual by 71 per cent to 0.130s and our S-wave rms residual by 59 per cent to 0.624s. At shallow sublithospheric depths we image several localized lower velocity regions, correlated with higher heat flow and interpreted as upwelling asthenosphere. We image a high velocity structure down to depths of about 350km beneath the Eastern Alps. Further east, beneath the Pannonian Basin, a deeper continuation of the Eastern Alps fast anomaly is imaged trending E-W from ∼300km depth and extending into the mantle transition zone (MTZ). In the MTZ we image a fast anomaly extending outwards as far as the Carpathians, the Dinarides and the Eastern Alps. This higher velocity mantle material is interpreted as being produced by a mantle downwelling, whose detachment from the lithosphere above may have triggered the extension of the Pannonian Basin. © 2011 The Authors. Geophysical Journal International © 2011 RAS.

Ren Y.,University of Leeds | Stuart G.W.,University of Leeds | Houseman G.A.,University of Leeds | Dando B.,RockTalk Imaging Ltd. | And 4 more authors.
Earth and Planetary Science Letters | Year: 2012

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence, extension and convective overturn in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region from P-wave finite-frequency teleseismic tomography to help constrain such geodynamical interactions. We have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. The data were recorded on 54 temporary stations deployed by the South Carpathian Project (2009-2011), 56 temporary stations deployed by the Carpathian Basins Project (2005-2007), and 131 national network broadband stations. The P-wave relative arrival times are measured in two frequency bands (0.5-2.0. Hz and 0.1-0.5. Hz), and are inverted for Vp perturbation maps in the upper mantle. Our images show a sub-vertical slab of fast material beneath the eastern Alps which extends eastward across the Pannonian basin at depths below ~300. km. The fast material extends down into the mantle transition zone (MTZ), where it spreads out beneath the entire basin. Above ~300. km, the upper mantle below the Pannonian basin is dominated by relatively slow velocities, the largest of which extends down to ~200. km. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone of SE Romania, intermediate-depth (75-180. km) seismicity occurs at the NE end of an upper mantle high velocity structure that extends SW under the Moesian Platform, oblique to the southern edge of the South Carpathians. At greater depths (180-400. km), a sub-circular high velocity anomaly is found directly beneath the seismicity. This sub-vertical high-velocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. No clear evidence of a residual slab is observed above the MTZ beneath the Eastern Carpathians. These observations suggest that intermediate-depth seismicity in Vrancea Zone is unlikely to be due to slab tearing, but rather could be explained by either gravitational instability or delamination of mantle lithosphere. © 2012 Elsevier B.V.

Hrubcova P.,Academy of Sciences of the Czech Republic | Sroda P.,Polish Academy of Sciences | Grad M.,University of Warsaw | Geissler W.H.,Alfred Wegener Institute for Polar and Marine Research | And 3 more authors.
Geophysical Journal International | Year: 2010

The Variscan orogeny is the major Middle to Late Palaeozoic tectonometamorphic event in central Europe, and the Bohemian Massif is the largest exposure of rocks deformed during this orogeny. The Bohemian Massif consists of the Saxothuringian, Barrandian and Moldanubian units. Adjacent to this massif in the southeast, the Western Carpathians form an arc-shaped mountain range related to the Alpine orogeny during the Cretaceous to Tertiary. The complex crustal-scale geological structure of the Variscan Bohemian Massif and the Western Carpathians, and especially their contact, were analysed in this study employing the data of the SUDETES 2003 international seismic refraction experiment. The analysed seismic data were acquired along the 740 km long, NW-SE oriented S04 profile that crossed the Bohemian Massif and the Western Carpathians before terminating in the Pannonian Basin. The data were interpreted by 2-D trial-and-error forward modelling of P waves, and additional constraints on crustal structure were provided by gravity modelling.The complex velocity structure derived in our analysis included low velocities of 5.85 km s-1 at the contact of the Saxothuringian and Barrandian units that reflect the presence of low-density granites. There are distinct lateral variations in deep crustal structure in the transition between the Bohemian Massif and the Western Carpathians. The abrupt change of the crustal thickness in this transition zone may be associated with the Pieniny Klippen Belt, a deep-seated boundary between the colliding Palaeozoic lithospheric plate to the north and the ALCAPA microplate to the south. In the upper crust of this transition, low velocities of 4 km s-1 extend to 6 km and represent the sedimentary fill of the Carpathian Flysch and Foredeep that thins towards the foreland. This basin is also expressed as a pronounced gravity low. The Moho in the Carpathians reaches a depth of 32-33 km. In contrast, in the Pannonian Basin the Moho rises to a depth of 25 km, which corresponds to the Pannonian gravity high. © 2010 The Authors Geophysical Journal International © 2010 RAS.

Karbon M.,Vienna University of Technology | Bruckl E.,Vienna University of Technology | Hegedus E.,Eotvos Lorand Geophysical Institute | Preh A.,Vienna University of Technology
Natural Hazards and Earth System Science | Year: 2011

On 12 February 2008, a landslide occurred along a 50 m high bank of the Danube river near Dunaszekcsö, Hungary. The initial state is only incompletely documented and the geodetic data acquired after the mass movement are sparse. A generalized 3-D topographic model of the landslide and its surrounding area was assembled and a representative longitudinal profile extracted. The reconstruction of the original surface is based on an orthophoto as well as on morphological considerations. Recorded observations include the locations of the outcrops of basal sliding surfaces, displacements at the main scarp and in the lower part of the slide, and a value to describe the total mass transport. Such sparse and inhomogeneous data were insufficient to derive a comprehensive documentation of the landslide or obtain adequate constraints for an accurate numerical analysis. Therefore, slider block models were fitted to the field data, which have only a small number of free parameters. A general view on the morphology of the mass movement justifies its classification as a rotational slide. A double slider block model fits all observational parameters within their error margin and supplies valuable information on the geometry of the slide. Estimates of the residual friction angles were derived and the question of reactivation was addressed. Finite Difference (FD) modelling and the application of conventional stability analysis support the geometry of the slider blocks and the computed average residual friction angles. Generally, the results are assumed to represent preliminary information, which could only be attained by the combination of the thinly distributed geodetic data with qualitative morphological observations and the implementation of a model. This type of information can be gained quickly and may be valuable for preliminary hazard mitigation measures or the planning of a comprehensive exploration and monitoring program. © Author(s) 2011.

Csontos A.,Eotvos Lorand Geophysical Institute | Sugar D.,University of Zagreb | Brkic M.,University of Zagreb | Kovacs P.,Eotvos Lorand Geophysical Institute | Hegymegi L.,Eotvos Lorand Geophysical Institute
Annals of Geophysics | Year: 2012

One of the main challenges on the course of the repeat station surveys is to determine the spatial differences of the geomagnetic elements between the repeat stations and the reference observatory. The difficulty arises from the fact, that the directly obtained differences are affected not only by spatial but also by temporal effects of external origin. The error deriving from the external effects can be efficiently diminished by the installation of an on-site vector variometer. In this case the spatial difference can be computed for night-time period, when the external field is less varying (both spatially and temporally) than during daytime. Installation of the on-site variometer in the field requires the fulfillment of nearly the same conditions as in the observatories, i.e. the control of the reference frame, the scale factors, the offsets, and the temperature effects of the magnetometer. The principle of the fluxgate and DIDD magnetometers is quite different from each other, therefore the two devices provide different possibilities to obtain accurate result. The paper discusses some of the possible instrumental errors and offers a method based on the DIDD technology for the determination of the reference frame of a portable recording station. We analyse real records measured during the joint Hungarian-Croatian repeat station survey. © 2012 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved.

Heilig B.,Eotvos Lorand Geophysical Institute | Lotz S.,Hermanus Geomagnetic Observatory | Lotz S.,Rhodes University | Vero J.,Hungarian Academy of Sciences | And 4 more authors.
Annales Geophysicae | Year: 2010

It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of ground-level Pc3-4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and ground-based magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during low-density events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves. © Author(s) 2010.

In this note, a simple method is introduced for the determination of the pitch angle between two coil axes by means of a total field magnetometer. This method is applicable when the homogeneous volume inside the coils is large enough to accommodate the sensor of a total field magnetometer. The orthogonality of calibration coil systems used for calibration of vector magnetometers can be calibrated by this procedure. The method can be easily automated and applied for the calibration of delta inclination-delta declination (dIdD) magnetometers. © 2012 IOP Publishing Ltd.

Berta M.,Eötvös Loránd University | Kiraly C.S.,Eötvös Loránd University | Falus G.Y.,Eotvos Lorand Geophysical Institute | Juhasz G.Y.,Mol Nyrt. | Szabo C.S.,Eötvös Loránd University
Energy Procedia | Year: 2011

One of the largest storage potential for CCS is in the deep saline aquifers because their pore water cannot be used for drinking and for agricultural activities. In the Pannonian Basin (Hungary) there are sedimentary sub-basins filled up by sedimentary rock sequences containing such aquifers, which have the main potential for CCS in Hungary. Our chosen study area in the Pannonian Basin was the Jászság Subbasin, well known by numerous seismics and hydrocarbon exploration wells. As Hungary is situated in the middle of the Pannonian Basin, its emissions could be significantly reduced by CCS. That is the main reason to find a suitable place for CCS. The process filling up the basin resulted in a sedimentary system from deep-water to deltaic sediments, including thick facies units of reservoir quality as well as thick facies units acting as seals above it. During the evolution of the basin, large rivers brought huge amounts of sediments from the NE and NW towards the deeper parts of Lake Pannon, forming huge deltas on the river mouths. The potential reservoir formations now form a hidrogeologically coherent regional system, indicating a large potential for storage capacity. Furthermore, the saline aquifer system is large enough to ensure its long-term industrial usage for CCS, because the injection does not cause critical increase in the pressure. However, the system is not homogenous: there are siltstone interbeddings both in the Algyo″ (clayey cover formation), and the Szolnok Formations (dominantly sandstone), as we could see on well-logs of HC exploration wells. The siltstone in these formations does not have porosity high enough to be the storage rock, whereas the permeability is not low enough to be a good cap rock. That is why we try to avoid sampling siltstone-rich regions in the whole Jászság Basin. On the other places, and depth intervals we have used drilling cores to get a realistic quality and representative quantity of the tested formations. Our detailed studies deal with the sandy Szolnok Formation, and the clayey Algyo″ Formation. The Szolnok Fm. is mainly formed by sandstone, its bottom is nearly 1000 to 3500 m deep under the surface, thus it would be used as a storage rock. Its cap rock (seal) is the Algyo″ Fm. with more than 1000 m thickness, and a clayey composition. These potential rock associations are examined in detail in our ongoing research. We will do ex situ tests observing the behavior of the rocks when injecting supercritical CO2 in the saline pore water on pressure and temperature representing the depth of planned injection conditions. © 2011 Published by Elsevier Ltd.

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