GFZ Underground Laboratory in the Research and Education Mine “Reiche Zeche” Freiberg

The GFZ Underground Laboratory is operated by the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences. It is located in the research and education mine “Reiche Zeche” in Freiberg, Germany allows testing of geophysical and geotechnical tools and methods in boreholes and galleries. The lab is ideally suited for seismic system components such as receivers and sources for three-dimensional high resolution seismic imaging and tomography surveying. The lab layout of a basement rock block surrounded by galleries around a vertical as well as two horizontal boreholes enables the realization of various underground survey geometries e.g. well-to-well and well-to-gallery. The galleries are equipped with thirty 3-component geophone anchors installed in 1 m and 2 m depths for tomographic measurements or the recording of radiation pattern of seismic borehole sources

Seismic imaging in the Krafla high-temperature geothermal field, NE Iceland, using zero- and far-offset vertical seismic profiling (VSP) data

The research leading to these results has received funding from the European Community's Seventh Framework Program under grant agreement No. 608553 (Project IMAGE). We thank Landsvirkjun, the operator of the Krafla geothermal field, for technical and logistical support during the survey. We also thank the Operational Support Group of the International Continental Scientific Drilling Program (ICDP) for their technical support. We further acknowledge the support from the Research Council of Norway through its Centres of Excellence funding scheme, project 22372 (SP).Peer reviewedPostprin

Rayleigh-to-shear wave conversion at the tunnel face - from 3D-FD modeling to ahead-of-drill exploration

For a safe tunnel excavation it is important to predict lithological and structural heterogeneities ahead of the construction. conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). In this work we propose a new prediction strategy that has been discovered by 3-D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face are converted into high amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the side walls. We name these waves RSSR waves. In our approach the front face acts as a S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multi-modal reflection response. For the detection of geological interfaces ahead RSSR waves recorded along the side walls are corrected for dispersion and stacked. From the arrival times the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been successfully verified in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geological surveying and exploratory drilling

Modellbau jungsteinzeitlicher Häuser aus Norddeutschland im Archäologisch-Ökologischen Zentrum Albersdorf. Rekonstruktive Grundlage, Erfahrungen und Probleme aus der Praxis

Since 1997 the "Archaeological-Ecological Centre Albersdorf" (AÖZA) in the county of Dithmarschen in Schleswig-Holstein,  Germany, is working on the aim to re-establish a Neolithic cultural landscape (c. 3000 BC) on an area of about 40 hectares. One concrete and important step for the project is to build a "Neolithic village" as a model in original scale and as an open-air museum in the immediate vicinity of original prehistoric grave monuments. The article describes the aims and the scientific base of the "Neolithic" house models following the relatively well preserved structures of houses in Flögeln-Eekhöltjen and Pennigbüttel in Lower Saxony. The experiences of the work (material, methods and problems) are discussed and the possible effects for knowledge and mediation of prehistoric house building for the public are shown

Seismic anisotropy of Opalinus Clay: tomographic investigations using the infrastructure of an underground rock laboratory (URL)

Seismic anisotropy and attenuation make claystone formations difficult to characterize. On the other hand, in many geotechnical environments, precise knowledge of structure and elastic properties of clay formations is needed. In crystalline and rock salt underground structures, high-resolution seismic tomography and reflection imaging have proven a useful tool for structural and mechanical characterization at the scale of underground infrastructure (several deca- to hundreds of meters). This study investigates the applicability of seismic tomography for the characterization of claystone formations from an underground rock laboratory under challenging on-site conditions including anisotropy, strong attenuation and restricted acquisition geometry. The seismic tomographic survey was part of a pilot experiment in the Opalinus Clay of the Mont Terri Rock Laboratory, using 3-component geophones and rock anchors, which are installed 2 m within the rock on two levels, thus suppressing effects caused by the excavation damage zone. As a source, a pneumatic impact source was used. The survey covers two different facies types (shaly and carbonate-rich sandy), for which the elliptical anisotropy is calculated for direct ray paths by fitting an ellipse to the separated data for each facies. The tomographic inversion was done with a code providing a good grid control and enabling to take the seismic anisotropy into account. A-priori anisotropy can be attributed to the grid points, taking various facies types or other heterogeneities into account. Tomographic results, compared to computations using an isotropic velocity model, show that results are significantly enhanced by considering the anisotropy and demonstrate the ability of the approach to characterize heterogeneities of geological structures between the galleries of the rock laboratory.BMBF, 02NUK053D, Verbundprojekt iCross: Integrität von Endlagersystemen für radioaktive Abfälle - Skalenübergreifendes Systemverständnis und Systemanalyse, Teilprojekt

Sub-surface geology and velocity structure of the Krafla high temperature geothermal field, Iceland : Integrated ditch cuttings, wireline and zero offset vertical seismic profile analysis

The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). The VMAPP project run by VBPR, DougalEARTH Ltd. and TGS also contributed funding to the borehole characterization of the K-18 borehole. Landsvirkun is acknowledged for their effort and assistance in this work and in particular for allowing the use of the data from well K-18. We further acknowledge the support from the Research Council of Norway through its Centres of Excellence funding scheme, project 22372 (SP and DAJ).Peer reviewedPostprin

Seismic prediction ahead of a tunnel face - Modeling, field surveys, geotechnical interpretation

An important precondition for underground construction is a detailed knowledge of the soil and/or rock conditions in the area of the construction. In order to overcome existing limitations in classical exploration methods, research and development for exploration ahead of a tunnel face focuses on: hardware development for excavation integrated measurements, modelling and processing of data measured under these specific circumstances, and integrative interpretation of seismic results with other data from the excavation, from geological mapping, and from exploratory drilling, where available. Finite difference modelling of seismic wavefields around tunnels has shown the general feasibility of seismic measurements for imaging structures ahead of a tunnel face. The modelling results were confirmed by field measurements in various tunnel sites. The integrated interpretation of seismic data with all available geological and geotechnical information is currently in the state of development and aims, in the middle to long term perspective, at an “a priori” detection of structures ahead of the face

Hindcast of the 1976/77 and 1998/99 climate shifts in the Pacific

The use of a coupled ocean/atmosphere/sea-ice model to hindcast (i.e. historical forecast) recent climate variability is described and illustrated for the cases of the 1976/77 and 1998/99 climate shift events in the Pacific. The initialization is achieved by running the coupled model in partially coupled mode whereby global observed wind stress anomalies are used to drive the ocean/sea-ice component of the coupled model while maintaining the thermodynamic coupling between the ocean/sea-ice and atmosphere components. Here we show that hindcast experiments can successfully capture many features associated with the 1976/77 and 1998/99 climate shifts. For instance, hindcast experiments started from the beginning of 1976 can capture sea surface temperature (SST) warming in the central-eastern equatorial Pacific and the positive phase of the Pacific Decadal Oscillation (PDO) throughout the 9 years following the 1976/77 climate shift, including the deepening of the Aleutian low pressure system. Hindcast experiments started from the beginning of 1998 can also capture part of the anomalous conditions during the 4 years after the 1998/99 climate. We argue that the dynamical adjustment of heat content anomalies that are present in the initial conditions in the tropics is important for the successful hindcast of the two climate shifts

Geotechnologien - Innovative Technologien zur Erkundung des Untergrundes, Verbundvorhaben: ONSITE - On-line seismic imaging system for tunnel excavation in hard rock

[no abstract available