Entwicklung einer simultanen refraktions- und reflexionsseismischen 3D-Laufzeittomographie mit Anwendung auf tiefenseismische TRANSALP-Weitwinkeldaten aus den Ostalpen

A 3D refraction and reflection seismic travel time tomography was developed on the basis of the widespread Local Earthquake Tomography (LET) method SIMULPS. To include crustal scale refraction seismic observations in the inversion the accuracy of this method was adjusted for long ray paths and high resolution. Floating or discontinuous reflectors are modelled on separate grids by bi-cubic splines, and an appropriate reflection ray tracer was developed using the Approximate Ray Tracing/Pseudo Bending (ART/PB) method. Accuracy was adjusted by several means: arcuate ART trajectories are roughly adjusted to the velocity field before bending, multiple ART travel time minima are perturbed and step length along the ray path for distant observations is reduced by iterative resegmentation. The resulting ray tracer also finds head waves as long as interface geometry is not too complex. The extensions have been tested with some simple synthetic models focusing on problems connected with discontinuities and low velocity zones. The inversion algorithm was then applied to a wide-angle data set from the Eastern Alps recorded by seismological three-component stations during the TRANSALP campaign. From Vibroseis records a high resolved model for the upper crust was derived, which was extended to depth with low resolution using distant observations from dynamite shots. The resulting model correlates well with known geologic structures in the upper crust. The middle and lower crust shows distinct velocity functions for the European and the Adriatic part of the profile. The European Moho is resolved from the Northern Calcareous Alps in 40 km depth to the Alpine root in ca. 55 km depth, where it seems to lose its reflective character. Only few reflections from the Adriatic Moho were recorded yielding a depth of ca. 40 km. Lower crustal structure is interpreted as a result of southward subduction of Penninic oceanic crust before collision.Auf der Basis einer weitverbreiteten Methode der Lokalbebentomographie (SIMULPS) wurde eine simultane 3D-Tomographie für refraktierte und reflektierte Laufzeiten entwickelt. Die Genauigkeit dieser Methode wurde den Bedüfnissen der hochauflösenden Krustenrefraktionsseismik angepasst. Reflektoren werden mit bi-kubischen Splines auf separaten Gittern parameterisiert. Ausgehend von den Approximate Ray Tracing/Pseudo Bending (ART/PB) Methoden der Strahlmodellierung wurde ein geeigneter Reflexionsraytracer entwickelt. Die Erhöhung der Genauigkeit erfolgte durch eine grobe Anpassung der kreisförmigen ART-Trajektorien an das Geschwindigkeitsfeld, die Auswertung mehrerer ART-Laufzeitminima sowie die verfeinerte Diskretisierung des Strahlwegs für entfernte Beobachtungen. Der resultierende Strahlmodellierer findet auch Kopfwellen, solange die Geometrie nicht zu komplex ist. Die Erweiterungen wurden anhand von synthetischen Daten getestet, wobei ein Schwerpunkt auf der Betrachtung von Problemen im Zusammenhang mit Reflektoren und Niedriggeschwindigkeitszonen lag. Der Inversionsalgorithmus wurde dann auf einen Weitwinkeldatensatz aus den Ostalpen angewandt, der im Rahmen der TRANSALP-Messungen von seismologischen 3K-Stationen aufgezeichnet wurde. Aus Vibroseisregistrierungen konnte ein hochauflösendes Modell der Oberkruste gewonnen werden, das mit geringer Auflösung auf der Basis sprengseismischer Beobachtungen in die Tiefe fortgesetzt wurde. Das Ergebnismodell zeigt in der Oberkruste eine gute Übereinstimmung mit geologischen Befunden. Die Geschwindigkeitsverteilung der mittleren und tiefen Kruste zeigt deutliche Unterschiede zwischen dem europäischen und dem adriatischen Teil. Die Europäische Moho kann von den Nördlichen Kalkalpen, wo sie sich in etwa 40 km Tiefe befindet, bis zum Hauptkamm in 55 km Tiefe verfolgt werden. Südlich davon scheint sie ihren reflektiven Charakter zu verlieren. Mit nur wenigen reflexionsseismischen Beobachtungen wurde die Tiefe der adriatischen Moho auf 40 km bestimmt. Die Struktur der tiefen Kruste wird als Ergebnis einer südgerichteten Subduktion penninischer ozeanischer Kruste und anschließender Kollision interpretiert

Fault Detection with Crosshole and Reflection Geo-Radar for Underground Mine Safety

Ground-penetrating radar and crosshole radar are applied in an underground marble mine for fault detection and to test if different geological bodies can be distinguished. Boreholes are often drilled in advance of mining to clarify the locations of ore bodies and gangues. Here, such boreholes were used for crosshole investigations to supplement optical borehole imaging. Four boreholes were drilled along a profile with increasing offsets from 5 to 25 m. The crosshole measurements were performed with 100 MHz antennas. Tomographic panels were created up to a depth of 28 m and were complemented by reflection mode ground-penetrating radar (GPR) measurements along a 25 m-long profile with 100 and 250 MHz antennas. The GPR imaging successfully delineates the fault and karstification zones with higher water content due to their strong dielectric permittivity contrast compared to the surrounding geology

A stratigraphic link between the NE Greenland and Mid-Norwegian continental margins based on reflection seismic and borehole data

During the last decades, the Norwegian-Greenland Sea has been a focus of research. Beside commercial interest in hydrocarbon exploration, the region is important for the understanding of the Cenozoic climate evolution from the opening of the North Atlantic at approximately 55 Ma to the late-Cenozoic glaciations. In 2003, the research vessel “Polarstern” conducted a seismic survey along the NE Greenland shelf and slope during expedition “ARKTIS XIX leg 4a”. We reprocessed seven seismic profiles from this data set applying multiple suppression, radon transformation and time migration. Furthermore, a seismic net consisting of 13 processed profiles along the Mid-Norwegian margin with a special focus on the Vøring Plateau area reaching into deep sea were provided by the Norwegian Petroleum Directorate (NPD). The NPD profiles served as a link between the deep-sea parts of the NE Greenland and Norwegian margins for a seismo-stratigraphic correlation, based on its reflection characteristics and P-wave velocity distribution from Eocene to Pleistocene times. Borehole data of the Deep Sea Drilling Project (DSDP) and its successor, the Ocean Drilling Program (ODP) supported reflection seismic correlation between the two continental margins via sonic velocities from log measurements (if available) and stratigraphic correlations among borehole data based on previous literature researches, shipboard scientific reports and initial reports. Based on these data sets, an updated Cenozoic stratigraphic model of the NE Greenland continental margin could be derived. The results should ease and encourage selections of drilling spots and offshore seismic data acquisition in future, since both will contribute to a more detailed picture of the Cenozoic strata and the geological evolution of the Norwegian-Greenland Sea