Field campaign Kinzig valley
Introduction
Abb. 1: Location of work area between Vogelsberg and Spessart
In Oktober 2006 the University of Frankfurt and the former GGA istitute carried out a geoelectrical field experiment in the Kinzig valley (AGRICOLA et al 2006, 2007). We used dipole-dipole arrays with dipole lengths of about 50m. The maximum dipole distance was about 1.5km. Injection was done with a programmable high-voltage source (SÜDEKUM et al. 2004) with up to 40A at 1000V. The signals were registered continuously using the data logger GEOLORE (ROßBERG et al. 2004) in three dipole directions (see below). In summary 22 injections at 8 positions were accomplished and registered at 11 stations resulting in a total of 726 single data.
Geology and station layout
Abb. 2: Geology of the Kinzig valley and experimental layout: Measuring stations (green triangles) and injection points (black points)
Data processing
By extensive techniques the measured signals have been processed. First, the active signals are cut and filtered. Second, the resistance is determined by Fourier analysis of current and potential time series'. With a new approach also an error is estimated, which is used as weighting factors in the inversion with the finite difference software DC3dInvRes (Günther, 2004). Figure 3 shows a preliminary result.
Figure 3: First inversion result. In the shallow part (-35m) the reservoir and underlying sediments show up. From a depth down to 225m we observe a NE-SW striking good conductive zone. From 300m on the ground is conductive in the Northwest and resistive in the Southeast. This can be a hint for a fault.
References (mainly in german)
AGRICOLA, T.; SCHÜNEMANN, J.; JUNGE, A. (2006): Großflächige Gleichstrommessungen an Land und im Wasser:Technische Aspekte. Mitteilungen der Deutschen Geophysikalischen Gesellschaft
Nr. 4/2006: 6-17.
AGRICOLA, T.; SCHÜNEMANN, J.; JUNGE, A. (2007): Großräumige gleichstromgeoelektrische Messungen in einem Flachsee. Poster-Präsentation auf der Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 2007. Abstract, Poster
EHRENBERG, K.-H. & HICKETHIER, H. (1982): Erläuterungen zur Geologischen Karte von Hessen 1:25.000 Blatt Nr.5622 Steinau a. d. Str. - Hess. Landesamt f. Bodenforschung.
GÜNTHER, T. (2004): Inversion Methods and Resolution Analysis for the 2D/3D Reconstruction of Resistivity Structures from DC Measurements, PhD Thesis, University of Mining and Technology, Freiberg
ROßBERG, R.; GOLDEN, S.; BEBLO, M. (2004): Datensammeln, fast ohne Energie: Geolore - Ein batteriegestützter Datenlogger für wissenschaftliche Messwerterfassung. - Elektronik 18: 78-86.
SCHÜNEMANN, J.; GÜ NTHER, T.; JUNGE, A.(2007): 3-dimensional subsurface investigation by means of large-scale tensor-type dc resistivity measurements. - 4th International Symposium on Three-Dimensional Electromagnetics, Freiberg.
SÜDEKUM, W., BROST, G., SAUER, J., WORZYK, P. & GRINAT, M. (2004): Eine programmierbare Hochstromquelle - mit 50 A von DC bis AC - GGA-Institut, www.gga-hannover.de
Authors
Thomas Agricola & Thomas Günther, after a (german) poster:
Agricola, Junge, Günther, Schünemann (2008): Aufbereitung großer gleichstromgeoelektrischer Datensätze im Frequenzbereich - Poster, 68. Jahrestagung der Deutschen Geophysikalischen Gesellschaft in Freiberg (Sachsen), 03.-06.03.08
a page in the project large scale resistivity investigation