Brandes C.,Leibniz University of Hanover |
Tanner D.C.,Leibniz Institute for Applied Geophysics
Earth-Science Reviews | Year: 2014
Folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts, accretionary wedges, fold-and-thrust belts, and intra-plate settings in either strike-slip, compressional, or extensional regimes. Due to their widespread occurrence, knowledge about the development of these structures is important to a broad spectrum of geoscience sub-disciplines, such as structural geology, seismology, geomorphology, petroleum geology, and Quaternary geology. Fault-related folding has been analyzed intensively over the last 140. years. For the sake of this review, we divide the folds according to the way the faults and the folds form; that is into detachment, fault-bend, and fault-propagation folds.All fault-related folds are caused by changes in fault parameters. The simplest method to produce folds is to transport material along faults that have stepped, flat-ramp-flat geometries (fault-bend fold). Alternatively the slip can decrease along the length of the fault, and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy, either a detachment fold or a fault-propagation fold is formed, respectively.Detachment folding was first investigated in the early 20th Century, whereas the full significance of fault-propagation folds was recognized quite late in the 1980s. Seminal work on fault-related folding was carried out in the 1930s, but quantitative kinematic models have only been available in the last 30. years. These models are extremely valuable, because they allow a comprehensive understanding of the evolution of fault-related folds and lead to more accurate predictions of the sub-surface structure. From the mid-1990s onwards, numerical simulations have been used to identify how fault parameters (such as dip and fault-bend angle, propagation-to-slip ratio, and shape of the trishear zone) influence the geometry of the related folding. This is directly applicable to the analysis of the shape of anticlines produced. However, this does not mean that fold geometry is uniquely related to fault geometry; on the contrary, different kinematic approaches can lead to a similar fold shape. © 2014 Elsevier B.V.
Muller-Petke M.,Leibniz Institute for Applied Geophysics |
Dlugosch R.,Leibniz Institute for Applied Geophysics |
Yaramanci U.,Leibniz Institute for Applied Geophysics
New Journal of Physics | Year: 2011
The technique of nuclear magnetic resonance (NMR) has found widespread use in geophysical applications for determining rock properties (e.g. porosity and permeability) and state variables (e.g. water content) or to distinguish between oil and water. NMR measurements are most commonly made in the laboratory and in boreholes. The technique of surface NMR (or magnetic resonance sounding (MRS)) also takes advantage of the NMR phenomenon, but by measuring subsurface rock properties from the surface using large coils of some tens of meters and reaching depths as much as 150 m. We give here a brief review of the current state of the art of forward modeling and inversion techniques. In laboratory NMR a calibration is used to convert measured signal amplitudes into water content. Surface NMR-measured amplitudes cannot be converted by a simple calibration. The water content is derived by comparing a measured amplitude with an amplitude calculated for a given subsurface water content model as input for a forward modeling that must account for all relevant physics. A convenient option to check whether the measured signals are reliable or the forward modeling accounts for all effects is to make measurements in a well-defined environment. Therefore, measurements on top of a frozen lake were made with the latest-generation surface NMR instruments. We found the measured amplitudes to be in agreement with the calculated amplitudes for a model of 100% water content. Assuming then both the forward modeling and the measurement to be correct, the uncertainty of the model is calculated with only a few per cent based on the measurement uncertainty. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Rucker C.,TU Berlin |
Gunther T.,Leibniz Institute for Applied Geophysics
Geophysics | Year: 2011
Direct-current resistivity surveys usually are performed using steel rods of finite extent and grounding resistance. However, in modeling, electrodes are commonly treated as ideal point sources. We present an approach for numerical computation applying the complete electrode model (CEM), which is known from medical imaging. The electrode surface was discretized, and the partial-differential equations were extended by additional relations incorporating a contact impedance and a condition for the current flow through the electrode surface. We verified the modeling of the electrical potential using an analytical solution for a perfectly coupled half-ellipsoid current source. To quantify the influence of a finite electrode, we computed the electrode effect as the ratio between CEM and point-source solution and investigated its dependence on geometry and contact impedance. Surface measurements using rods of typical spatial extent showed electrode effects on the order of the measuring accuracy for an electrode length/spacing ratio lower than 0.2. However, the effects are more significant for closed geometries such as experimental tanks. A comparison with a point approximation for finite electrodes using point-source locations along the electrode axis showed the best agreement, with points at about 60% of the electrode extension. The contact impedance played a minor role for four-point measurements, contributing only a few percent to the electrode effect. In addition to penetrating electrodes, we investigated surface electrodes with galvanic or capacitive coupling, showing electrode effects on the same order as for penetrating electrodes. An inhomogeneous resistivity distribution clearly increased the size of the effects. We also investigate the use of CEM to simulate current injected through steel-cased boreholes. Finally, we applied the approach with buried ring electrodes to calculate effects caused mainly by geometric disturbances from the borehole. © 2011 Society of Exploration Geophysicists.
Hubner W.,Leibniz Institute for Applied Geophysics
Journal of Applied Geophysics | Year: 2014
Evaluating the formation quality by deriving porosity, pore size, and permeability from cuttings instead of drill cores is a promising and challenging field of research established in the past decade. Challenges with cuttings are their small and irregular size rendering them unsuitable for e.g. standard permeability measurements. Permeability can be estimated from nuclear magnetic resonance (NMR) measurements. NMR measurements on cuttings are especially challenging 1) because the total NMR signal is very low due to small sample sizes and 2) because the high ratio of outer surface to volume leads to a significant contribution of interstitial water to the NMR signal, which thus distorts the informative NMR signal from within the pore space. The aim of the study is to evaluate the use of NMR in combination with micro-computed tomography (μCT) as a method to determine the pore space characteristics of small drill cuttings from the Bückeberg Formation (German Wealden). After accurate removal of interstitial water and a CT based sorting, it was possible to measure NMR signals representative for the individual pore sizes. The representiveness of the measured values was verified by simulations of the NMR signals in pore spaces determined via μCT. Porosity, relaxation time distributions, and permeability were calculated for cuttings assemblages with large, medium, small, and very small pores. © 2014 Elsevier B.V.
Barta G.,ELTE Institute of Geography and Earth science |
Barta G.,Leibniz Institute for Applied Geophysics
Quaternary International | Year: 2014
Micro- and macroscale secondary carbonates were investigated from the loess-paleosol sequence of Sütto, Hungary. As secondary carbonates are formed in pedosedimentary environments, they designate how the microecosystem adapts to dust accretion. Besides pedogenic aspects, the hints of diagenesis can be tracked, especially concerning leaching effects. The main goal of this study was to make an attempt whether the distribution-related signals of secondary carbonates combined with their genetic properties can be used for paleoenvironmental reconstruction. The elaborated method is wet sieving of bulk loess/paleosol samples in order to: 1) separate secondary carbonates to describe morphological properties, partly with the help of scanning electron microscopy and 2) provide a depth-related semiquantitative distribution. The semiquantitative distribution is ordered to the marine isotope stage units of the Sütto sequence (MIS 6 to 2). The MIS 6 section is characterized by presumably slower dust accumulation and raises the possibility of a multiphase leaching history throughout the profile. Lower dust accumulation rates with increasing aridity are assumed upwards in MIS 5. MIS 4 is typified by arid conditions and the alternation of lower and higher dust accumulations. Certain properties of paleosol development and frost deformation related to secondary carbonates can be distinguished in MIS 3. Dust accumulation rates are presumed to be consistent upwards in this section. During MIS 2, different sedimentation stages are distinguished, but generally they show a decreasing trend upwards to the modern soil. This work serves as a complementary method which may help to refine the paleoenviromental signals of the Sütto loess-paleosol sequence to determine relative sedimentary phases. The limitations of the method have to be taken into consideration, as the results are semiquantitative. © 2013 Elsevier Ltd and INQUA.
Wacha L.,Leibniz Institute for Applied Geophysics |
Frechen M.,Leibniz Institute for Applied Geophysics
Quaternary International | Year: 2011
Along the right bank of the Danube River in Croatia up to 30 m thick loess-palaeosol sequences are exposed. A detailed geochronological study was performed on the "Gorjanović loess section" at Vukovar by the means of infrared stimulated luminescence (IRSL) dating. The section consists of loess intercalated by three palaeosols and a tephra layer. Fourteen samples were collected and dated using the elevated temperature post-IR IRSL protocol, a modified single aliquot regenerative dose (SAR) protocol, for the equivalent dose (De) determination on fine-grained polymineral material. Both the IRSL signal at 50 °C and the post-IR IRSL signal at 225 °C were recorded. Fading tests were performed for both signals and the ages were fading-corrected. The loess/palaeosol sequence can be correlated to the penultimate glacial - last interglacial - last glacial period (MIS6-MIS2). An even older loess record at the site under study was previously described but is not exposed anymore owing to the embankment. The fading-corrected IRSL and the fading-corrected post-IR IRSL results are in excellent agreement. The post-IR IRSL signal at 225 °C shows less fading than the IRSL signal at 50 °C and can successfully be used for the dating of older loess. © 2011 Elsevier Ltd and INQUA.
Gunther T.,Leibniz Institute for Applied Geophysics |
Muller-Petke M.,Leibniz Institute for Applied Geophysics
Hydrology and Earth System Sciences | Year: 2012
For reliably predicting the impact of climate changes on salt/freshwater systems below barrier islands, a long-term hydraulic modelling is inevitable. As input we need the parameters porosity, salinity and hydraulic conductivity at the catchment scale, preferably non-invasively acquired with geophysical methods. We present a methodology to retrieve the searched parameters and a lithological interpretation by the joint analysis of magnetic resonance soundings (MRS) and vertical electric soundings (VES). Both data sets are jointly inverted for resistivity, water content and decay time using a joint inversion scheme. Coupling is accomplished by common layer thicknesses. We show the results of three soundings measured on the eastern part of the North Sea island of Borkum. Pumping test data is used to calibrate the petrophysical relationship for the local conditions in order to estimate permeability from nuclear magnetic resonance (NMR) data. Salinity is retrieved from water content and resistivity using a modified Archie equation calibrated by local samples. As a result we are able to predict porosity, salinity and hydraulic conductivities of the aquifers, including their uncertainties. The joint inversion significantly improves the reliability of the results. Verification is given by comparison with a borehole. A sounding in the flooding area demonstrates that only the combined inversion provides a correct subsurface model. Thanks to the joint application, we are able to distinguish fluid conductivity from lithology and provide reliable hydraulic parameters as shown by uncertainty analysis. These findings can finally be used to build groundwater flow models for simulating climate changes. This includes the improved geometry and lithological attribution, and also the parameters and their uncertainties. © Author(s) 2012.
Reimann T.,Free University of Berlin |
Reimann T.,Leibniz Institute for Applied Geophysics |
Tsukamoto S.,Leibniz Institute for Applied Geophysics
Quaternary Geochronology | Year: 2012
The applicability of the post-IR IRSL single-aliquot regenerative-dose protocol (termed pIRIR protocol) has been tested on K-rich feldspar from recent coastal sediment samples (<500 a) from the southern North Sea coast and southern Baltic Sea coast. The most suitable post-IR IRSL (pIRIR) stimulation temperature is found to be 150 °C by using a preheat temperature of 180 °C. For this pIRIR stimulation temperature, a detectable pIRIR signal is obtained and the residual dose is minimized. Furthermore, anomalous fading is found to be negligible in the pIRIR 150 signal for our young samples whereas the fading rates for the conventional IRSL signal measured at 50 °C (IRSL 50) is between 5 and 7%/decade. However, the pIRIR 150 signal bleaches significantly slower compared to the IRSL 50, according to bleaching experiments using daylight, solar simulator and IR diodes, although the residual doses of both signals are similar. The laboratory residual doses in perfectly bleached aliquots are variable from sample to sample and vary between 300 ± 170 and 800 ± 460 mGy for the pIRIR 150. The precision of the residual dose determination is generally poor and causes large uncertainties on the residual subtracted ages. The laboratory residual doses alone cannot account for the observed overestimation in our two youngest samples (<70 a), indicating that the feldspar signals in these samples were presumably not fully bleached prior to aeolian or beach deposition. However, even if the age uncertainties are large we obtained pIRIR 150 ages in agreement with independent age estimates for the two older samples, which are 70 and 390 years old. © 2012 Elsevier B.V..
Ehret B.,Leibniz Institute for Applied Geophysics
Geoderma | Year: 2010
A new rock classification method for ground penetrating radar (GPR) data is presented for cases where no additional geological information is available from boreholes. There are non-linear relationships between petrophysical properties of rocks and electromagnetic waves which can be handled using two methods derived from statistical learning theory on pattern recognition. An investigation was carried out looking at proving the feasibility of the method in principle for use on synthetic models as well as measurement data. The different learning methods were also compared. The method is based on multivariate statistical learning algorithms for the discrimination of layer boundaries between different rocks. The discrimination developed works with artificial neural networks (ANN) and support vector machines (SVM). The processing procedure starts with geological models with varying petrophysical rock parameters, which are to be sought in the measurement data. The models are used to generate synthetic radargrams from which rock properties can be derived using wave attributes. The calculated values of the wave attributes are stored in a multivariate data pool. This data pool is used to train the ANN and the SVM. The same wave attributes are derived from the GPR data and also saved in a data pool. This generates two data sets for pattern recognition with which to directly classify rock layers. Wave attributes can therefore be used to derive the non-linear correlative relationships between rock properties and GPR data by the weighted matrices of ANN and SVM. The presented method can be used to match reflections in the GRR data directly with the layer boundaries of rock formations. The classification of a boundary horizon between rock salt and anhydrite is demonstrated on synthetic GPR traces and measurement data from a rock salt mine. The advantage of this method is that rock classification is not a priori dependent on borehole data. © 2009 Elsevier B.V.
News Article | December 21, 2016
DFG to fund 12 projects for the development of new technologies through new call/ New major research instrument for X-raying reinforced concrete components approved The Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) is funding new instrumentation for various fields of knowledge-driven research through two calls. The Joint Committee of the largest research funding organisation and central self-governing organisation of the research community in Germany took the relevant funding decisions at its December session in Bonn. The first decision relates to the call for "New Instrumentation for Research", issued for the first time, which is designed to enable the development of new instrumentation technologies for research questions which cannot be answered with currently available equipment. The newly developed instrumentation should be made available to as many researchers as possible for the purposes of basic research. After the very strong response to the call issued in January 2016 - which attracted a total of 79 proposals - the DFG Joint Committee has now decided to fund twelve projects for an initial three years with a total funding volume of €8 million. The projects relate to natural sciences (including geosciences), life sciences, medical technology, and engineering sciences and are based at the following universities and non-university research institutions: Aalen University; Charité - Universitätsmedizin Berlin (university hospital); University of Bonn; Technical University of Darmstadt; Erlangen University Hospital, University Medical Center Freiburg and Radiological Institute, German Cancer Research Centre, Heidelberg; Leibniz Institute for Applied Geophysics, Hanover, and Leibniz Institute of Photonic Technology, Jena; Heidelberg University; University of Jena; University of Cologne, Leibniz Institute for Astrophysics, Potsdam, and Landessternwarte Königstuhl (state observatory), Heidelberg; Technical University of Munich, University of Greifswald and Max Planck Institute of Plasma Physics, Greifswald; University Hospital Münster; University of Würzburg and University of Mainz. The second decision relates to a major instrumentation initiative. Through this initiative, the DFG will make €8 million available for the construction and commissioning of a new type of system at the Technical University of Kaiserslautern that will be able to X-ray components made of reinforced concrete and other materials using computed tomography (CT). The system will use X-rays of 9 mega-electronvolts, much more powerful than medical X-ray systems, allowing it to probe reinforced concrete components up to 30 centimetres in diameter and 6 metres in length. It will even be possible to X-ray components while they are experiencing stress or destruction; the three-dimensional images of these processes will provide researchers with valuable information. The research carried out with the new equipment is intended to provide information about the durability and properties of established construction materials and also facilitate the development of improved materials and composites. For 20 percent of its usage time, the new X-ray system will also be available to other scientific working groups in Germany. For "New Instrumentation for Research": Dr Achim Tieftrunk, Scientific Instrumentation and Information Technology Division, tel. +49 228 885-2816, Achim.Tieftrunk@dfg.de For the major instrumentation initiative: Dr Michael Royeck, Scientific Instrumentation and Information Technology Division, tel. +49 228 885-2976, Michael.Royeck@dfg.de