Near Surface 2005 - 11th European Meeting of Environmental and Engineering Geophysics

A006 Four dimensional inversion of dc resistivity monitoring data Abstract 1 Dc resistivity monitoring has been increasingly used in order to understand the changes of subsurface conditions in terms of conductivity. An approach commonly used is to construct the time-lapse images by independently inverting the measured data acquired at different times. This may result in the time-lapse images contaminated with inversion artifacts. In this paper I propose an algorithm to invert all data sets simultaneously from a long-term monitoring survey. Accordingly we can obtain all the subsurface models at different times by just one inversion process. As a measure of

A008 MODELLING OF MRS SIGNALS OVER 2D ELECTRICALLY CONDUCTIVE STRUCTURES Abstract 1 We show for the first time modellings of Magnetic Resonance Sounding (MRS) data influenced by 2D electrical resistivity structures. We demonstrate exemplarily the impact of a 2D electrical resistivity distribution for two typical geological situations: a horizontal block and a dipping layer. We also show the influence of the dipping direction that can be especially seen in the phase values. For studies on 2D water content distributions it is also recommended to consider the associated 2D resistivity distribution. Method Magnetic Resonance Sounding (MRS or Surface Nuclear Magnetic Resonance

A010 GEOELECTRIC SURVEYS TO SUPPLEMENT TO DETERMINE THE STRUCTURE OF HYDRO- THERMAL SYSTEMS – CASE STUDY VULCANO Abstract 1 Geophysical methods provide the tools to investigate 3D volcanic structures and corresponding hhdrothermal systems. Even though seismic and gravimetric data have proven to supply valuable information the application of additional potential field methods is of great benefit for improving this picture. Geoelectric multi-electrode tomographic sections give a detailed image of the subsurface resistivity distribution. The Geological Survey of Austria (GBA) has a huge expertise in this field applied to volcanic areas. From 1996 to 2004 the GBA has conducted dozens of

A012 AIRBORNE EM – FROM ANOMALY HUNTING TO 3D MAPPING – A CASE FROM FINLAND Abstract 1 GTK (Geological Survey of Finland) started the Finnish low-altitude airborne geophysical mapping program in 1972. Nearly 90 percent of the land area has been measured so far. During the last ten years airborne EM (AEM) data have turned into a base material in many ground water land use and environmental mapping and monitoring projects. Recent improvements in measurement and interpretation techniques have been giving rise to detailed subsurface conductivity models and expanded the use of AEM data to new applications. This paper discusses

A014 MONITORING OF A GROUNDWATER TRACER USING RADIOMAGNETOTELLURICS (RMT) Summary 1 In autumn 2002 a large amount of saltwater was injected into a shallow unconfined aquifer for a period of 7 days. The experiment was accompanied by extensive geophysical monitoring for 10 weeks before during and after the injection. Radiomagnetotelluric field data display a conducting anomaly progressing with the groundwater flow. A comparable anomaly appears in the conductivities determined by groundwater probing. The RMT data have been interpreted using a two-dimensional magnetotelluric inversion code. Inversion results supply detailed information on the heterogeneous geological structure of the aquifer and reveal a

A016 Frequency electromagnetic modelling to study moisture zones in salt mines 1 G. KURZ (1) R. SCHULZ (2) and U. YARAMANCI (1) (1) Technical University Berlin Dep. of Applied Geophysics Ackerstr. 71 D-13355 Berlin Germany (2) Leibniz Institute for Applied Geosciences Stilleweg 2 D-30655 Hannover Germany [email protected] Abstract To investigate the stability of mining buildings in salt mines (e.g. galleries pillars caverns chambers) detection and observation of moisture zones is necessary. These zones decreases the natural stability of rock salt and are often responsible for collapsing of parts of the mining building. The electromagnetic method is an useful tool for

A018 Time-lapse Monitoring using Borehole-to- Surface Electrical Resistivity Tomography Abstract 1 Time-lapse Electrical Resistivity Tomography (ERT) has been applied in borehole-to-surface mode to study the leachate generation within an unconfined landfill near Thriplow U.K. Several boreholes were drilled in the landfill to characterize the waste and to establish the concentration and spatial variability of the leachate. To assist this study six of these boreholes were instrumented by installing an electrode array on the outside of the PVC casing prior to completion. Borehole-to surface ERT were collected over two periods (January and April) using mainly Wenner-Schlumberger The data were processed using

A020 Z-99 Mapping resistivity variation to identify sulphidic sediments in Sweden. Introduction 1 Sulphidic postglacial sediments occur below the highest coastline in both Finland and Sweden. The sediments were mainly deposited in the Litorina Sea from about 7000 to 4000 years ago. Acid sulphate soils are formed after oxidation of the iron sulphides (e.g. FeS FeS2) in these sediments. High concentrations of certain trace elements (e.g. Ni Cu and Mn) have been measured in streams which drains areas dominated by acid sulphate soils [9]. These trace elements can cause environmental problems. Figure 1. Location of the Study area in the

A022 The quantitative capabilities of HEM inversion for the sea ice case Summary 1 Semi-empirical methods are routinely used for Helicopter Electromagnetic (HEM) sea ice thickness mapping. Although these methods yield sufficiently accurate thickness data it is of interest to determine whether formal one-dimensional (1D) geophysical inversion could yield improved results. If both the thickness and the ice conductivity could be mapped the results could be used to estimate glaciological parameters such as the age of the sea ice. Sea ice conductivity data could also be potentially used to estimate the strength of the ice sheet which would be valuable

A024 A TRIPLE-GRID TECHNIQUE FOR THE 3D INVERSION OF DC RESISTIVITY DATA INCOPORATING ARBITRARY TOPOGRAPHY Summary 1 We present a novel technique for the determination of resistivity structures associated with arbitrary surface topography. The approach represents a triple-grid dc resistivty inversion technique which is based on unstructured tetrahedral meshes and a finite element forward operator applied to the secondary potential. We use a Gauss-Newton method with inexact line search to fit the data within error bounds. A global regularization scheme using special smoothness constraints is applied. The regularization parameter compromising data misfit and model roughness is determined by an L-curve