Am 16. April 2020 sollte das Leipziger Kolloquium „Forschung in der Geotechnik“ an der HTWK Leipzig stattfinden. Ab Frühjahr 2020 konnten viele Ideen aufgrund der Ausbreitung des Coronavirus SARS-CoV-2 und der damit einhergehenden Beschränkungen nicht verwirklicht werden – so auch diese Veranstaltung. Uns war es als Veranstalter jedoch wichtig, die eingereichten Beiträge als Open-Access-Publikation anzubieten. Die hier gebündelten Kurzbeiträge sind als Ausschnitt der derzeitigen Forschung in der Geotechnik zu verstehen. Sie behandeln Themen wie Ersatzbaustoffe, Bodenverdichtungen, optische und seismische Methoden, Ansätze für die Zustandsbeschreibung, für Simulationen und das Verhalten von Böden und Pfählen. Dies zeigt, wie stark die Geotechnik sich in vielen Richtungen spezialisiert hat. Und wie notwendig der fachliche Austausch daher bleibt.

A VSP test experiment at the high temperature geothermal field Krafla in NE-Iceland has been carried out. In two boreholes a zero-, far-, and multi-offset VSP were applied to assess the applicability of VSP as a method for delineating subsurface structures like magmatic bodies, zones of supercritical fluids, superheated steam, and high permeability in volcanic geothermal fields. Because of high well temperatures (>150°C) and high attenuating surface layers, challenging field preparations were necessary. Three-component seismic data were recorded with a sufficient signal-to-noise ratio and dominant signal frequencies around 20 Hz and 40 Hz, down to 2200 m depth, for air gun and explosive sources, respectively. As a result, the data provide a good basis for several processing and imaging techniques. As part of this Master\'s thesis, standard and novel processing techniques of a subset of the data (zero and far-offset VSP in a single well) have been tested and show promising results in accordance with the lithology from well data. Besides velocity profiles and a corridor stack for both P- and S-waves were determined, a 3D Kirchhoff depth migration and Fresnel volume migration have been applied and tested. Already for a single source location, results show structures in the vicinity and below the well, and it can be assumed that further interpretation and data integration will provide a great potential in addition to hitherto applied teleseismic and potential methods. Especially, for geothermal sites it has been shown, that VSP can be applied and provide information of geometries where dipping faults and fracture zones are expected. The research leading to these results has received funding from the European Community\'s Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE).

An lehmigen Modelldeichen mit beliebig variierbaren Hochwasserbelastungen wurde ein Monitoring mit einer hochauflösenden Seismik durchgeführt. Der Vergleich von Deichmessungen während des ungefluteten Zustandes mit Messungen bei hohen Wasserständen und starker Durchfeuchtung der Deiche zeigt einen starken Einfluss auf das seismische Wellenfeld mittels deutlicher Dämpfung der Signale in Bereichen des Deichkörpers mit hoher Durchfeuchtung und einer Abnahme der P-Wellengeschwindigkeiten mit zunehmender Durchfeuchtung des Deiches. Es konnte gezeigt werden, dass Dichte, Kompressions- und Schermodul einen Hauptteil der deutlichen Abnahme der P-Wellengeschwindigkeit mit zunehmendem Wassergehalt bewirken. Mit Laufzeit-Tomographien bei unterschiedlichen Hochwasserbelastungen lassen sich die verschiedenen Durchfeuchtungszustände der Modelldeiche nachvollziehen.

A VSP test experiment at the high temperature geothermal field Krafla in NE-Iceland has been carried out. In two boreholes a zero-, far-, and multi-offset VSP were applied to assess the applicability of VSP as a method for delineating subsurface structures like magmatic bodies, zones of supercritical fluids, superheated steam, and high permeability in volcanic geothermal fields. Because of high well temperatures (>150°C) and high attenuating surface layers, challenging field preparations were necessary. Three-component seismic data were recorded with a sufficient signal-to-noise ratio and dominant signal frequencies around 20 Hz and 40 Hz, down to 2200 m depth, for air gun and explosive sources, respectively. As a result, the data provide a good basis for several processing and imaging techniques. As part of this Master\'s thesis, standard and novel processing techniques of a subset of the data (zero and far-offset VSP in a single well) have been tested and show promising results in accordance with the lithology from well data. Besides velocity profiles and a corridor stack for both P- and S-waves were determined, a 3D Kirchhoff depth migration and Fresnel volume migration have been applied and tested. Already for a single source location, results show structures in the vicinity and below the well, and it can be assumed that further interpretation and data integration will provide a great potential in addition to hitherto applied teleseismic and potential methods. Especially, for geothermal sites it has been shown, that VSP can be applied and provide information of geometries where dipping faults and fracture zones are expected. 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 aim of the thesis is to study the response of Swedish buttress dams if they are subjected to an earthquake of relevant magnitude to Sweden. Swedish dams are evaluated for an extensive amount of load cases, but not for earthquake loading. Therefore, it is not known how the Swedish buttress dams would respond during such loading. Earthquake engineering is practised only to a marginal extent in Sweden due to a low risk of major earthquakes. In fact, an earthquake hazard zonation map that provides data for earthquake resistant design, does not even exist for Sweden. Therefore, part of the thesis is aimed at acquiring data from alternative sources to enable seismic evaluation. The effect of earthquakes on Swedish buttress dams are analysed through case studies. The case studies are performed with numerical analysis using the commercial finite element program Brigade Plus. The case studies are performed on two buttress dam models that were selected based on an inventory of Swedish buttress dams. In the case studies, the dam models are evaluated for the Safety Evaluation Earthquake (SEE), which correspond to 10 000 years return period. At the SEE event, the Peak Ground Acceleration (PGA), is also related to the geographical location of a dam. The envelope of available PGA in Sweden was used in the case studies to cover the spectrum of PGA. The response of the dams to the lowest value of PGA is insignificant and the dams are essentially unaffected. However, for the highest value of PGA the responses indicates that the concrete of the dams is severely cracked and that the ultimate capacity of the reinforcement may be exceeded. Hence, it is concluded that the geographical location of a Swedish dam is highly influential on the response to earthquake loading. / Syftet med denna uppsats är att analysera effekten på svenska betonglamelldammar i det fall de utsätts för en jordbävning av relevant magnitud för Sverige. Svenska dammar har blivit utvärderade för ett stort antal lastfall, dock ej för jordbävningslaster. Det är därför inte känt hur svenska betonglamelldammar uppträder under sådana laster. Jordbävningsdimensionering tillämpas endast marginellt i Sverige eftersom det föreligger låg risk för kraftfulla jordbävningar. Faktum är att en zonindelningskarta över jordbävningsrisk för byggnadsdimensionering inte ens existerar i Sverige. Därför dedikeras en del av uppsatsen till att hitta data från alternativa källor för seismisk utvärdering. Effekten av jordbävningar på svenska betonglamelldammar analyseras genom fallstudier. Dessa är genomförda baserat på numerisk analys med det kommersiella finita element programmet Brigade Plus. Analyserna är baserade på två utvalda betonglamelldammodeller som valdes genom en inventering av svenska betonglamelldammar. I fallstudien utvärderas dammarna för en Säkerhet Utvärderings Jordbävning (SUJ), denna motsvaras av 10 000 års återkomsttid. Vid en SUJ relateras den Maximala Mark Accelerationen (MAA) även till det geografiska läget av en damm. Ytterlighetsvärdena av tillgänglig MMA värden i Sverige användes i fallstudien för att täcka in hela spektrumet. Effekten av det lägsta MMA värdet på dammarna är obetydlig och dammarna kan anses i stort sett opåverkade. Det högsta värdet av MMA indikerar dock att dammarnas betong utsätts för stor uppsprickning och att kapaciteten av armeringen överskrids. Det kan därmed fastslås att det geografiska läget av en damm har stort inflytande över vilken effekt som kan förväntas vid en jordbävning

Im Rahmen des hydrogeologischen Projektes ResiBil wurde das Zittauer Gebirge geologisch untersucht. Das Zittauer Gebirge – als Teil des Sächsisch-Böhmischen Kreidebeckens – liegt im Kreuzungsbereich der Elbezone und des Egergrabens. Hierdurch treten komplexe tektonische Verhältnisse auf, die in dieser Arbeit u. a. erforscht wurden. Es wurden vor allem seismische, geoelektrische und gravimetrische Messungen in Deutschland und Tschechien vorgenommen, um die Lausitzer Überschiebung genauer zu untersuchen. Die Publikation richtet sich an die geologisch interessierte Öffentlichkeit. Redaktionsschluss: 13.09.2020

This study is concerned with the computation of seismic first-arrival traveltimes in anisotropic media using finite difference eikonal methods. For this purpose, different numerical schemes that directly solve the eikonal equation are implemented and assessed numerically. Subsequently, they are used for pre-stack depth migration on synthetic and field data. The thesis starts with a detailed examination of different finite difference methods that have gained popularity in scientific literature for computing seismic traveltimes in isotropic media. The most appropriate for an extension towards anisotropic media are found to be the so-called Fast Marching/Sweeping methods. Both schemes rely on different iteration strategies, but incorporate the same upwind finite difference Godunov schemes that are implemented up to the second order. As a result, the derived methods exhibit high numerical accuracy and perform robustly even in highly contrasted velocity models. Subsequently, the methods are adapted for transversely isotropic media with vertical (VTI) and tilted (TTI) symmetry axes, respectively. Therefore, two different formulations for approximating the anisotropic phase velocities are tested, which are the weakly-anisotropic and the pseudo-acoustic approximation. As expected, the pseudo-acoustic formulation shows superior accuracy especially for strongly anisotropic media. Moreover, it turns out that the tested eikonal schemes are generally more accurate than anisotropic ray tracing approaches, since they do not require an approximation of the group velocity. Numerical experiments are carried out on homogeneous models with varying strengths of anisotropy and the industrial BP 2007 benchmark model. They show that the computed eikonal traveltimes are in good agreement with independent results from finite difference modelling of the isotropic and anisotropic elastic wave equations, and traveltimes estimated by ray-based wavefront construction, respectively. The computational performance of the TI eikonal schemes is largely increased compared to their original isotropic implementations, which is due to the algebraic complexity of the anisotropic phase velocity formulations. At this point, the Fast Marching Method is found to be more efficient on models containing up to 50 million grid points. For larger models, the anisotropic Fast Sweeping implementation gradually becomes advantageous. Here, both techniques perform independently well of the structural complexity of the underlying velocity model. The final step of this thesis is the application of the developed eikonal schemes in pre-stack depth migration. A synthetic experiment over a VTI/TTI layer-cake model demonstrates that the traveltime computation leads to accurate imaging results including a tilted, strongly anisotropic shale layer. The experiment shows further that the estimation of anisotropic velocity models solely from surface reflection data is highly ambiguous. In a second example, the eikonal solvers are applied for depth imaging of two-dimensional field data that were acquired for geothermal exploration in southern Tuscany, Italy. The developed methods also produce clear imaging results in this setting, which illustrates their general applicability for pre-stack depth imaging, particularly in challenging environments.

Sind Geothermiebohrungen nicht fündig, bedeutet dies, dass das Wasser im Untergrund nicht die während der Projektplanung prognostizierte Temperatur hat bzw. nicht in ausreichender Schüttung zu Tage gefördert werden kann. Die Folgen sind meist der Projektabbruch und hohe finanzielle Verluste für den Investor. Beim Bohren nach Öl und Gas bringt schon jetzt nur eine von sieben Erkundungsbohrungen das gewünschte Ergebnis. Da die noch vorhandenen Öl- und Gasvorkommen immer schwieriger zu erschließen sind, steigen mit dem Risiko von Fehlbohrungen die Kosten und damit folgerichtig auch die Brennstoffpreise. Ein Grund für die aufgezeigte Problematik ist, dass die bisher in Bohrgarnituren eingesetzten Messgeräte zwar das Umfeld um die Bohrung, nicht aber den Bereich vor dem Bohrmeißel erkunden können. Seit Ende 2007 arbeitet eine Forschergruppe an einem neuen Messgerät, das in der Lage sein soll, seismische Energie gezielt in Bohrrichtung zu verstärken. Für die Manipulation der Abstrahlrichtung wird das bisher noch nicht in der Seismik genutzte Phased Array Prinzip angewandt. Die bisherigen Versuche im Labormaßstab waren erfolgversprechend. In der vorliegenden Arbeit wird untersucht, wie ein seismisches Messgerät in eine Bohrgarnitur integriert und im Feld eingesetzt werden könnte. Behandelt werden drei wesentliche Fragestellungen: (1) In welchem Bereich vor dem Bohrmeißel soll die seismische Energie verstärkt werden? Eine Richtbohrgarnitur kann zwar durch den Untergrund gelenkt werden, ihr Aktionsradius hängt jedoch von verschiedenen Randbedingungen ab. (2) An welcher Stelle in der Bohrgarnitur soll das Messgerät platziert werden? Ganz vorne befindet sich der Bohrmeißel, dahinter typischerweise die Steuer- und Messgeräte zur Richtungssteuerung der Garnitur, denn der Bohrpfad lässt sich umso genauer steuern, je geringer die Distanz zwischen diesen Geräten und dem Bohrmeißel ist. (3) Wann und wie soll gemessen werden? Jede zusätzlich für Messungen benötigte Zeitspanne ist ein Kostenfaktor, der die Bohrung verteuert. Die Versorgung des Messgeräts mit Energie und die Ansteuerung hängen darüberhinaus von der technischen Ausstattung der Bohrgarnitur und dem Zeitpunkt der Messung im Bohrprozess ab. Angesichts der Fragestellungen wird eine Analyse der bestehenden und neuen Systeme der Tiefbohrtechnik und der Seismik vorgenommen und auf dieser Grundlage ein ganzheitliches Modell entwickelt. Anhand dieses zentralen Modells werden mehrere Konzepte für Richtbohrgarnituren mit integriertem seismischem Messgerät erarbeitet sowie bewertet und die Wechselwirkungen zwischen Mess- und Bohrprozess untersucht. Ein Ergebnis der Arbeit ist die Definition des Begriffs „Vorauserkundung“. Um eine Vorauserkundung durchführen zu können, ist es wichtiger, das Messgerät in eine Richtbohrgarnitur zu integrieren, die hohe Bohrlochkrümmungen ermöglicht, als es so nahe wie möglich hinter dem Bohrmeißel zu platzieren. Mit den im Modell erarbeiteten Bewertungskriterien kann die Weiterentwicklung sowie die praktische Anwendung des seismischen Messgeräts begleitet und beurteilt werden.

This study is concerned with the computation of seismic first-arrival traveltimes in anisotropic media using finite difference eikonal methods. For this purpose, different numerical schemes that directly solve the eikonal equation are implemented and assessed numerically. Subsequently, they are used for pre-stack depth migration on synthetic and field data. The thesis starts with a detailed examination of different finite difference methods that have gained popularity in scientific literature for computing seismic traveltimes in isotropic media. The most appropriate for an extension towards anisotropic media are found to be the so-called Fast Marching/Sweeping methods. Both schemes rely on different iteration strategies, but incorporate the same upwind finite difference Godunov schemes that are implemented up to the second order. As a result, the derived methods exhibit high numerical accuracy and perform robustly even in highly contrasted velocity models. Subsequently, the methods are adapted for transversely isotropic media with vertical (VTI) and tilted (TTI) symmetry axes, respectively. Therefore, two different formulations for approximating the anisotropic phase velocities are tested, which are the weakly-anisotropic and the pseudo-acoustic approximation. As expected, the pseudo-acoustic formulation shows superior accuracy especially for strongly anisotropic media. Moreover, it turns out that the tested eikonal schemes are generally more accurate than anisotropic ray tracing approaches, since they do not require an approximation of the group velocity. Numerical experiments are carried out on homogeneous models with varying strengths of anisotropy and the industrial BP 2007 benchmark model. They show that the computed eikonal traveltimes are in good agreement with independent results from finite difference modelling of the isotropic and anisotropic elastic wave equations, and traveltimes estimated by ray-based wavefront construction, respectively. The computational performance of the TI eikonal schemes is largely increased compared to their original isotropic implementations, which is due to the algebraic complexity of the anisotropic phase velocity formulations. At this point, the Fast Marching Method is found to be more efficient on models containing up to 50 million grid points. For larger models, the anisotropic Fast Sweeping implementation gradually becomes advantageous. Here, both techniques perform independently well of the structural complexity of the underlying velocity model. The final step of this thesis is the application of the developed eikonal schemes in pre-stack depth migration. A synthetic experiment over a VTI/TTI layer-cake model demonstrates that the traveltime computation leads to accurate imaging results including a tilted, strongly anisotropic shale layer. The experiment shows further that the estimation of anisotropic velocity models solely from surface reflection data is highly ambiguous. In a second example, the eikonal solvers are applied for depth imaging of two-dimensional field data that were acquired for geothermal exploration in southern Tuscany, Italy. The developed methods also produce clear imaging results in this setting, which illustrates their general applicability for pre-stack depth imaging, particularly in challenging environments.

This thesis presents new insights into Alpine Fault structures at the drill site of the Deep Fault Drilling Project (DFDP)-2B at Whataroa in New Zealand. Despite the challenging conditions for seismic imaging within a glacial valley filled with sediments and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. The Alpine Fault at the West Coast in New Zealand is a major plate boundary forming a significant geohazard as large earthquakes (magnitude 7-8) occur regularly and the next earthquake is expected relatively soon. A major effort has been made to study the fault characteristics through scientific drilling in the Deep Fault Drilling Project (DFDP) Alpine Fault with the deepest DFDP-2B borehole located in the Whataroa Valley. A great variety of seismic data are newly acquired. First, the WhataDUSIE (Whataroa Detailed University Seismic Imaging Experiment) data set is a ~5 km long 2D profile acquired in 2011 prior to the drilling. As the 2D profile could not fully explain the 3D structures in the Whataroa Valley, an extended surface and borehole data set was acquired in 2016 after the drilling. This data set consists of shorter 2D lines (< 3 km), a dense 3D-array, and vertical seismic profiling (VSP) using the DFDP-2B borehole including the fibre-optic cable. 3D seismic data proved to be essential to understand the complex 3D structures of the glacial valley and the major fault. First-arrival travel time tomography and prestack depth migration (PSDM) are applied to obtain a P-wave velocity model and seismic images of the subsurface (<5 km). In this complex setting, the Fresnel volume migration (a focusing PSDM method) proved to best obtain structural information about the subsurface. Analysing the results of the seismic data processing, two major outcomes are achieved: improved knowledge about the glacial structures of the Whataroa Valley and structural images of the Alpine Fault zone. The Whataroa Valley is an overdeepened glacial valley with details of the basement topography visible in the seismic images. A deep trough is identified south of the DFDP-2B borehole with horizontal layering of the sediments. Valley flanks are identified in both the seismic images and the P-wave velocity model, particularly the western valley flank. Thus, Quaternary and glacial processes can be analysed with the help of the newly derived seismic images. The Alpine Fault is directly imaged with the seismic data, which is the first time in this region at shallow depths (<5 km). Several shorter fault segments between depths of 0.2 km and 2.2 km dipping 40-56° to the southeast are directly imaged. Further identified reflectors and faults are interpreted to represent Alpine Fault structures in the form of a damage zone and induced faults adding further complexity to the fault zone. In conclusion, the 3D seismic results presented in this thesis provide new insights into the Whataroa subsurface. Hence, the new results form a good basis for a deeper understanding of the Alpine Fault structures and underlying processes which is important for potential future drilling but also for the estimation of the geohazard in the region.