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Über dieses Buch

The research work on the topic of ‘‘Tomography of the Earth’s Crust: From Geophysical Sounding to Real-Time Monitoring’’ has focused on the development of cross-scale multiparameter methods and their technological application together with the development of innovative field techniques. Seismic wave field inversion theory, diffusion and potential methods were developed and optimized with respect to cost and benefit aspects.

This volume summarizes the scientific results of nine interdisciplinary joint projects funded by the German Federal Ministry of Education and Research in the framework of the Research and Development Program GEOTECHNOLOGIEN.

Highlights and innovations presented cover many length scales and involve targets ranging from applications in the laboratory, to ground water surveys of heterogeneous aquifer, geotechnical applications like tunnel excavation, coal mine and CO2 monitoring and the imaging and monitoring of tectonic and societally relevant objects as active faults and volcanoes.

To study these objects, the authors use the full spectrum of geophysical methods (ultrasonics, seismic and seismology, electromagnetics, gravity, and airborne) in combination with new methods like seismic interferometry, diffuse wave field theory and full-wave-form inversion in 3D and partially also in 4D.

Geophysical Sounding to Real-Time Monitoring’’ has focused on the development of cross-scale multiparameter methods and their technological application together with the development of innovative field techniques. Seismic wave field inversion theory, diffusion and potential methods were developed and optimized with respect to cost and benefit aspects.

This volume summarizes the scientific results of nine interdisciplinary joint projects funded by the German Federal Ministry of Education and Research in the framework of the Research and Development Program GEOTECHNOLOGIEN.

Highlights and innovations presented cover many length scales and involve targets ranging from applications in the laboratory, to ground water surveys of heterogeneous aquifer, geotechnical applications like tunnel excavation, coal mine and CO2 monitoring and the imaging and monitoring of tectonic and societally relevant objects as active faults and volcanoes.

To study these objects, the authors use the full spectrum of geophysical methods (ultrasonics, seismic and seismology, electromagnetics, gravity, and airborne) in combination with new methods like seismic interferometry, diffuse wave field theory and full-wave-form inversion in 3D and partially also in 4D.

2 monitoring and the imaging and monitoring of tectonic and societally relevant objects as active faults and volcanoes.

To study these objects, the authors use the full spectrum of geophysical methods (ultrasonics, seismic and seismology, electromagnetics, gravity, and airborne) in combination with new methods like seismic interferometry, diffuse wave field theory and full-wave-form inversion in 3D and partially also in 4D.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Broadband Electrical Impedance Tomography for Subsurface Characterization Using Improved Corrections of Electromagnetic Coupling and Spectral Regularization

Abstract
The low-frequency complex electrical conductivity in the mHz to kHz range has been shown to enable an improved textural, hydraulic, and biogeochemical characterization of the subsurface using electrical impedance spectroscopy (EIS) methods. Principally, these results can be transferred to the field using electrical impedance tomography (EIT). However, the required accuracy of 1 mrad in the phase measurements is difficult to achieve for a broad frequency bandwidth because of electromagnetic (EM) coupling effects at high frequencies and the lack of inversion schemes that consider the spectral nature of the complex electrical conductivity. Here, we overcome these deficiencies by (i) extending the standard spatial-smoothness constraint in EIT to the frequency dimension, thus enforcing smooth spectral signatures, and (ii) implementing an advanced EM coupling removal procedure using a newly formulated forward electrical model and calibration measurements. Both methodological advances are independently validated, and the improved imaging capability of the overall methodology with respect to spectral electrical properties is demonstrated using borehole EIT measurements in a heterogeneous aquifer. The developed procedures represent a significant step forward towards broadband EIT, allowing transferring the considerable diagnostic potential of EIS in the mHz to kHz range to geophysical imaging applications at the field scale for improved subsurface characterization.
Andreas Kemna, Johan A. Huisman, Egon Zimmermann, Roland Martin, Yulong Zhao, Andrea Treichel, Adrian Flores Orozco, Thomas Fechner

Chapter 2. Towards an Integrative Inversion and Interpretation of Airborne and Terrestrial Data

Abstract
The aim of the joint research project is to generate information from airborne geophysical measurements that are properly transferred from physically quantitative descriptions of the subsurface (electrical conductivities, densities, susceptibilities) into spatial structures and information matching the understanding of end-users: geologists, hydrogeologists, engineers and others. We suggest new types of inversion, which are integrated in the interactive workflow to support typical trial and error approaches of inverse and forward EM and gravity/magnetic field modelling for 1D and 3D cases. Subsequently, we combine resistivity and density models with geological 3D subsurface models. The integrated workflow minimizes uncertainties in the interpretation of geophysical data and allows a significantly improved and fast interpretation and imaging of the 3D subsurface architecture. The results of the AIDA project demonstrate that combined 3D geological and geophysical models enable a much better reconstruction of the subterraneous space. AIDA stands for “From Airborne Data Inversion to In-Depth Analysis” and is part of the R&D program: Tomography of the Earth’s Crust—From Geophysical Sounding to Real-Time Monitoring.
Hans-Jürgen Götze, Martin Afanasjew, Michael Alvers, Liliana Barrio-Alvers, Ralph-Uwe Börner, Christian Brandes, Rudolf Eröss, Peter Menzel, Uwe Meyer, Mathias Scheunert, Bernhard Siemon, Klaus Spitzer, Dominik Steinmetz, Johannes Stoll, Gupta Sudha, Bülent Tezkan, Angelika Ullmann, Jutta Winsemann

Chapter 3. MIIC: Monitoring and Imaging Based on Interferometric Concepts

Abstract
The capability of seismic interferometry to create virtual sources at receiver sites from records of ambient seismic noise is used for seismic monitoring and tomography of different targets. We present hardware developed specifically for the needs of seismic data acquisition in the context of monitoring and ambient noise tomography. Digitizers are capable of continuous recording and real time wireless data transmission in self organizing meshes to allow for robust telemetry in difficult circumstances such as cities or landslides that may cause the loss of stations. A software tool is described that implements required processing and analysis procedures for the interferometric processing. We have applied the novel 3D ambient noise surface wave tomography approach to the Issyk-Ata fault in Kyrgyzstan. It shows that seismic interferometry can successfully be used for structural investigations on length scales of only 100 m. The method uses 3D sensitivity kernels for a single-step inversion of phase velocity dispersion curves for subsurface S-wave velocity structure and incorporates topography. We recover lateral differences in sediment velocities and an offset of the bedrock depth across the fault. Applications of interferometric monitoring to the geological \(\mathrm{CO}_2\) storage test site in Ketzin (Germany) and to the Piton de la Fournaise volcano (La Reunion island) emphasize the value of this approach. At Ketzin site we identify variations of the subsurface velocities that are correlated with changes in the ground water level and mask potential signals from the reservoir depth. At Piton de la Fournaise volcano, seismic velocity changes are linked to volcanic processes as shown by comparison with surface displacement and seismicity that are typically used to characterize volcanic activity. We observe a clear distinction between phases of inflation prior to eruptions and deflation during periods of quiescence.
Christoph Sens-Schönfelder, Hortencia Flores-Estrella, Martina Gassenmeier, Michael Korn, Florian Köllner, Claus Milkereit, Ernst Niederleithinger, Stefano Parolai, Marco Pilz, Eraldo Pomponi, Andreas Schuck, Katja Thiemann, Jürgen Völkel

Chapter 4. The MINE Project: Monitoring Induced Seismicity in a German Coal Mine

Abstract
During the last thee years, the MINE project has developed and successfully applied seismological tools, addressing different aspects of the monitoring of mining environments, as dynamic local-scale systems. The human interaction with the shallow underground mining environment, can lead to rock mass weakening or locally induce stress perturbations. As a consequence, triggered or induced seismicity is often observed at mines, potentially posing a risk to miners and infrastructures. This work illustrates a number of recently developed seismological techniques, based on the analysis of full waveforms, which target the problem of detection, location, and characterization of mining-induced seismicity. The proposed methodologies are here discussed through their application to a 14-months coal mining dataset, affecting the region of Hamm, Ruhr, Germany. An automated full-waveform detection and location technique is first used to generate a seismic catalog. A full moment tensor amplitude spectra technique is then adapted for the analysis of induced seismicity, leading to the inversion of more than 1000 focal mechanisms. Finally, a new developed clustering algorithm is used to automatically classify source types, and to track their temporal evolution. The combined application of the methods developed within the MINE project could successfully characterise the mining-induced seismicity and its spatio-temporal variation. Our methods are suitable for automated analysis, and can be easily adopted for mining monitoring purposes in other locations, and with different network geometries.
Simone Cesca, Francesco Grigoli, Ali Tolga Şen, Samira Maghsoudi, Torsten Dahm, Thomas Meier

Chapter 5. Three-Dimensional Multi-Scale and Multi-Method Inversion to Determine the Electrical Conductivity Distribution of the Subsurface (Multi-EM)

Abstract
Combining different electromagnetic (EM) methods in joint inversion approaches can enhance the overall resolution power. Every method is associated with a particular sensitivity pattern. By assembling complementary patterns, subsurface imaging becomes more complete and reliable. We describe different paths to obtain multi-EM inversions. First, a joint inversion approach using finite difference forward operators is outlined that formulates the problem of minimizing the objective function using different weights for each individual method. Then we address a sequential approach using finite element methods on unstructured grids to cycle through the different EM methods iteratively. Both methods are based on a traditional parametrization using piecewise constant model parameters which may be inefficient when describing the usually rather coarse models. Therefore, we investigate wavelet-based model representations as an alternative.
Oliver Ritter, Klaus Spitzer, Martin Afanasjew, Michael Becken, Ralph-Uwe Börner, Felix Eckhofer, Michael Eiermann, Oliver G. Ernst, Alexander Grayver, Jens Klump, Naser Meqbel, Christian Nittinger, Jan Thaler, Ute Weckmann, Julia Weißflog

Chapter 6. MuSaWa: Multi-Scale S-wave Tomography for Exploration and Risk Assessment of Development Sites

Abstract
Near surface seismic imaging bears a high potential to enhance geotechnical site characterization. We highlight recent advances made in S-wave tomography for characterizing near surface unconsolidated sediments. This comprises progress in experimental setup and acquisition technology for local scale S-wave tomography. We discuss the development of mobile seismic crosshole tomography solely building on temporary installations realized by direct push technology as well as a modular borehole geophone chain suitable for operation in shallow and slim near surface boreholes. These technical developments are accompanied by progress in geophysical model generation, i.e., fully non-linear inversion strategies suitable for routine application and model uncertainty appraisal. We link S-wave and P-wave tomographic models to geotechnical target parameters and evaluate recent developments made for high resolution ground-truthing using direct push technology for geotechnical and stratigraphic analyses. To be able to provide improved regional scale seismic properties we advanced the Rayleigh wave based imaging of S-wave velocity variations using diffusive wavefield theory for modeling the full microtremor H/V spectral ratio for receivers at the surface and in depth.
Hendrik Paasche, Michael Rumpf, Agostiny M. Lontsi, Jörg Hausmann, Katrin Hannemann, Thomas Fechner, Matthias Ohrnberger, Ulrike Werban, Jens Tronicke, Frank Krüger, Peter Dietrich

Chapter 7. Seismic Tomography and Monitoring in Underground Structures: Developments in the Freiberg Reiche Zeche Underground Lab (Freiberg, Germany) and Their Application in Underground Construction (SOUND)

Abstract
The construction of large tunnels and underground infrastructures faces increasingly large dimensions and complex geological conditions. Under these conditions, exploration techniques are needed which enable for a detection of potentially hazardous structures during construction. Seismic sensors, integrated into rock anchors, and small seismic signal sources using defined pneumatic impulses or sweep signals generated by magnetostrictive actuators are the components of an exploration system which can be easily integrated into different types of underground excavation work and which can also be deployed for the long-term monitoring of already existing tunnels or caverns. However, for a continuous acquisition of seismic signals during tunnel excavation, the strong and broadband signal generated by a tunnel boring machine (TBM) may be used as a continuously operating source. Within the collaborative project SOUND, the seismic equipment at the Underground Lab of the Reiche Zeche Research Mine in Freiberg (Germany) has been used for a tomographic monitoring study during the excavation of an inclined gallery. A synthetic, but realistic seismic data set was simulated using a randomly heterogeneous velocity model which can be regarded as a realistic prototype of the velocity distribution in the real Gneiss block. The simulated acquisition geometry has been derived from the actual source and receiver point distribution in the Underground Laboratory. It can be shown that the analysis of the modelled seismic data by full waveform inversion (FWI) was able to reveal the lateral heterogeneity of the velocity model with significantly higher resolution compared to traveltime tomography of the direct P-wave arrivals. The analysis of field data from the Underground Laboratory has shown that there are complex interactions in close vicinity to the receiver location, and before FWI can be applied to this real data set, source and receiver dependant signatures need to be removed by inversion and deconvolution. A further field experiment, performed during gallery excavation in the Underground Laboratory, has shown that the setup of seismic receivers in rock anchors and a sparse array of adaptive vibro-sources is able to detect subtle changes in seismic wave propagation related to stress changes due to the excavation of an inclined gallery. After the deployment in the Underground Laboratory, a field survey was carried out on a tunnel construction site. A broadband seismic data set, using the tunnel boring machine could be acquired providing a basis for high resolution imaging of structures ahead of the construction site and geotechnical characterization of the imaged volume.
Stefan Lüth, Thomas Bohlen, Rüdiger Giese, Sven Heider, Silke Hock, Stefan Jetschny, Ulrich Polom, Sonja Wadas, Aissa Rechlin

Chapter 8. Toolbox for Applied Seismic Tomography (TOAST)

Abstract
TOAST (Toolbox for Applied Seismic Tomography) makes methods of full-waveform inversion of elastic waves available for the practitioner. The inversion of complete seismograms is an utmost ambitious and powerful technology. One of its strengths is the enormously increased imaging-resolution since it is able to resolve structures smaller than the seismic wave length. Further it is sensitive to material properties like density and dissipation which are hardly accessible through conventional techniques. Within the TOAST project algorithms available in academia were collected, improved, and prepared for application to field recordings. Different inversion strategies were implemented (global search, conjugate gradient, waveform sensitivity kernels) and computer programs for imaging the subsurface in 1D, 2D, and 3D were developed. The underlying algorithms for the correct numerical simulation of physical wave propagation have thoroughly been tested for artefacts. In parallel these techniques were tested in application to waveform data. They proved their potential in application to synthetic data, shallow-seismic surface waves from field recordings, and microseismic and ultrasonic data from material testing. This provided valuable insight to the demands on seismic observation equipment (repeatability, waveform reproduction, survey layout) and inversion strategies (initial models, regularization, alternative misfit definitions, etc.). The developed software programs, results of benchmark tests, and field-cases are published online by the OpenTOAST.de initiative.
Thomas Forbriger, Michael Auras, Filiz Bilgili, Thomas Bohlen, Simone Butzer, Sandra Christen, Luigia Cristiano, Wolfgang Friederich, Rüdiger Giese, Lisa Groos, Heiner Igel, Florian Köllner, Rolf Krompholz, Stefan Lüth, Stefan Mauerberger, Thomas Meier, Ilaria Mosca, Dirk Niehoff, Heike Richter, Martin Schäfer, Andreas Schuck, Florian Schumacher, Karin Sigloch, Mario Vormbaum, Frank Wuttke

Chapter 9. Tomographic Methods in Hydrogeology

Abstract
The extraction of groundwater for drinking water purposes is one of the most important uses of the natural subsurface. Sustainable management of groundwater resources requires detailed knowledge of the hydraulic properties within the subsurface. Typically, these properties are not directly accessible. The evaluation of hydraulic properties therefore requires hydraulic stimuli of the subsurface (e.g., injection and extraction of groundwater, tracer tests, etc.) with subsequent data analysis. In this context, tomographic techniques and inversion strategies originally derived for geophysical surveying can be transferred to hydraulic applications. In addition, geophysical techniques may be used to monitor hydraulic tests. The latter requires fully coupled hydrogeophysical inversion strategies, accounting for the entire process chain from hydraulic properties via flow and transport to the application of the geophysical surveying techniques. The project “Tomographic methods in hydrogeology” focuses on the development of a geostatistical inversion method for transient tomographic data of multiple hydraulic investigation techniques, the model-based optimal design of tomographic surveys, and the development of experimental techniques and equipment for an efficient execution of tomographic surveys in a hydrogeological context using the model-based design and providing data for the inversion. In this chapter we will show selected examples of the project’s outcome. The examples include developments related to the joint geostatistical inversion of tomographic data sets, its efficient parallelization, and its application to a 3D-inversion of tomographic thermal tracer tests. Furthermore we present a method for solving the inversion of transient tomographic data sets which usually suffer from high computational efforts. Related to the acquisition of tomographic data sets, we also discuss the development of tracer-tomographic methods using heat as tracer.
Olaf A. Cirpka, Carsten Leven, Ronnie Schwede, Kennedy Doro, Peter Bastian, Olaf Ippisch, Ole Klein, Arno Patzelt
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