ALBERT

Description: The purpose of this study is to refine the probabilistic seismic hazard assessment for Vanuatu. The analysis is complicated by inconsistencies of the global and local data for the investigated region and systematic inadequacies of the attenuation relation available. An additional aspect in the field of which more research would be desirable is the de-clustering algorithm for the identification of dependent earthquakes. In order to quantify the inevitable uncertainties associated with our results, we used a Logic Tree approach. The report is subdivided into seven chapters. Chapter 2 summarises the geology and tectonic setting of the Vanuatu island arc. Prior scientific investigations will be sketched briefly and to the degree to which they are relevant for our further considerations. The consecutive Chapter 3 describes the different data sources used for the calculations. Together, the local earthquake catalogue provided by the IRD (Institut de Recherche pour le D´eveloppement) and the global catalogues constitute a comprehensive data base for the region. The homogenisation of different catalogues required the conversion of magnitudes through maximum likelihood regressions. Chapter 4 gives a brief overview over the methodological concept applied. The implementation of the Cornell methodology involves two key steps: The first step is to construct a seismicity model (Chapter 5) including the definition of source zones and seismicity parameters characterising the level and type of activity in the respective zone. The second step is to determine an appropriate attenuation relation for the earthquake-generated ground motion in dependence of magnitude and distance. Chapter 6 compares several attenuation relations from the recent geophysical literature. We argue that the modeling of attenuation is the weakest link in this analysis and the major source of uncertainty. The new seismic hazard maps are presented and discussed in Chapter 7. The map that we consider to be the most relevant is also shown on the inner title page of this report. Our findings indicate that the seismic hazard in Vanuatu has been underestimated by prior assessments such as the Global Seismic Hazard Assessment Programme GSHAP (cf. Fig. 1.1).

Description: Bivergent wedges result from the interaction between deformation, flexure and surface processes. Based on 2D sandbox simulations in conjunction with PIV, this study investigates the influence of these processes on the spatio-temporal evolution of strain-partitioning within, and the associated surface uplift of, bivergent wedges. To facilitate interpretation and to successfully communicate results, two new display types, i.e., the surface uplift and the evolution of deformation map are introduced.

Description: Following work is embedded in the multidisciplinary study DESERT (DEad SEa Rift Transect) that has been carried out in the Middle East since the beginning of the year 2000. It focuses on the structure of the southern Dead Sea Transform (DST), the transform plate boundary between Africa (Sinai) and the Arabian microplate. In this work a short description of the seismic reflection method and the various processing steps is followed by a geological interpretation of the seismic data, taking into account relevant information from other studies.

Description: This thesis work describes a new experimental method for the determination of Mode II (shear) fracture toughness, KIIC, of rock and compares the outcome to results from Mode I (tensile) fracture toughness, KIC, testing using the International Society of Rock Mechanics (ISRM) Chevron-Bend (CB-) method. The fracture toughness describes the resistance of rock to fracturing. This parameter is therefore important when estimating the failure of rock and rock structures using rock fracture mechanics principles.

Description: The main objective of this thesis is an investigation and description of the secular variation of the Earth's magnetic field between 1980 and 2000. In particular, in the first part of this study the phenomenon of geomagnetic jerks are investigated by means of a deterministic model, which basically gives a description of the secular variation as a parameterization of typical periodicities of the external field. I argue that the conclusion drawn from this approach is not valid for explaining jerks as caused by external events and not valid to describe the global secular variation. In the second part a time--dependent model of the secular variation between 1980 and 2000 is developed. The endpoints of the time interval were chosen, because of the availability of high quality field models from satellite data for these epochs. The Gauss coefficients are expanded in time as function of cubic B--splines. This model is forced to fit field models from high quality vector measurements from MAGSAT in 1980 and OERSTED in 2000. The methodology is new. The model is a valuable extension of the hitherto existing time--dependent description of the secular variation, the GUFM which was valid until 1990. Unlike GUFM the model is based on observatory monthly means, and the knot spacing of the cubic B--Splines tighter than GUFM. Therefore it reveals a short term secular variation on subdecadal time scale, which was not as yet resolved. The model is also valuable to test the frozen flux hypothesis and to link some of the morphology of the radial field at the core--mantle boundary to the geodynamo. The third part of this thesis deals with the inversion of the time--dependent field and secular variation model for different kinds of core surface flow. These flows allow prediction of the decadal change of the length of the day, an observable which is independent to geomagnetic data. The prediction of some of the flows have the right tendency, but differ in slope from the observed change of the length of the day.

Description: The Central European Basin System is one of the basins where the sedimentary cover is strongly affected by salt tectonics. The most significant stage of salt movement occurred during the Triassic. The largest Triassic subsidence occurred in the different sub-basins surrounding the Ringkoebing-Fyn High such as the Horn Graben, the Danish Basin and the Glueckstadt Graben. Furthermore, the thickest Triassic succession is observed in the Glueckstadt Graben where it reaches more than 9000 m. In the present study, the structure and the Permian to recent evolution of the Glueckstadt Graben are investigated by use of borehole data, seismic lines and 3D structural modelling. The evaluation of the diverse deformation patterns of the sedimentary cover and their relations to salt structures show that the strongest salt movements occurred at the beginning of the Keuper when the Gluckstadt Graben was affected by extension. The onlap patterns of the Jurassic sediments onto the top of the Keuper succession indicate essential changes of the sedimentation style during the Jurassic. Thick Jurassic sediments are only observed around salt structures and are thinning away from salt walls or salt stocks. The Upper Cretaceous strata have an approximately constant thickness and the parallel reflections patterns indicate a quiet tectonic setting with very minor salt movements in the Late Cretaceous. Renewed salt flow during the Paleogene-Neogene caused rapid subsidence along the marginal parts of the Central Triassic Graben in the Westholstein, the Eastholstein and the Hamburger troughs. The thick Paleogene-Neogene strata within the marginal troughs may also be related to a regional component of tectonic subsidence in the area, contemporary with rapid subsidence in the North Sea. The 3D modelling approach has been used to determine salt distribution at certain paleo-levels in response to unloading due to sequential removing of the stratigraphic layers. The modelling approach was also aimed to reconstruct the original Permian salt distribution immediately after deposition. The initial salt thickness varies from 1300 m at the flanks of the basin up to 3000 m within the central part and demonstrates a clear NNE-SSW trend of the basin. The regional trend of the restored salt distribution points to a westward continuation of the Permian salt basin. The formation of the deep Central Triassic Graben and the subsequent Jurassic- Cenozoic marginal troughs was strongly controlled by the development of salt structures through time. It is shown that the depocentre of sedimentation was moving away from the central part of the of the original Graben structure towards its margins. The evaluation of the available data and results of the 3D reverse modelling demonstrate that a greater amount of subsidence occurred close to the active salt structures, and may have resulted in gradual depletion of Permian salt. Thus, this study indicates that the source of such long-term subsidence is derived from gradual depletion of the Permian salt, which started within the axial part of the basin and moved towards the basin flanks with time. In this sense, the Glueckstadt Graben was formed at least partially as a “basin-scale rim syncline” during post-Permian times. Therefore, the results show that salt withdrawal may have played an important role during the Meso-Cenozoic evolution and that the effects of salt-driven subsidence during the Meso-Cenozoic can be considered the main reason for the formation of the deep Central Triassic Graben and the subsequent Jurassic-Cenozoic marginal troughs.

Description: Das zentraleuropäische Beckensystem ist eines der Becken, in denen die Sedimentdecken stark durch Salztektonik beeinflusst sind. Die stärksten salztektonischen Aktivitäten traten während der Trias auf. Die größte triassische Subsidenz erfolgte in den verschiedenen Unterbecken rund um das Ringköbing-Fünen Hoch (Horn Graben, Dänisches Becken, Glückstadt Graben). Die mächtigste triassische Abfolge wurde im Glückstadtgraben beobachtet, wo sie mehr als 9000 m Mächtigkeit erreicht. In der vorliegenden Studie wurden die Struktur sowie die Entwicklung des Glückstadt Grabens vom Perm bis heute mit Hilfe von Bohrdaten, seismischen Linien und 3D-Strukturmodellierung untersucht. Die Auswertung der verschiedenen Deformationsmuster der Sedimentdecke und ihr Bezug zu Salzstrukturen zeigen, dass die stärksten Salzbewegungen am Beginn des Keupers, während einer Dehnung des Glückstadt Graben auftraten. Die jurassischen Sedimente zeigen dann eine grundlegende Änderungen der Sedimentationsart während des Jura an. Mächtige jurassische Sedimente treten nur rund um Salzstrukturen auf und dünnen mit zunehmender Entfernung von Salzmauern oder Salzstöcken aus. Die Oberkreideschichten haben eine annähernd konstante Mächtigkeit, und die parallelen Reflektionsmuster weisen auf eine ruhige tektonische Subsidenz mit geringen Salzbewegungen in der Oberkreide hin. Erneute Salzbewegungen während des Paläogens-Neogens verursachten schnelle Subsidenz entlang der Randbereiche des zentraltriassischen Grabens, den Westholstein, Ostholstein und Hamburger Trögen. Die mächtigen paläogen-neogenen Schichten innerhalb der Randtröge sind eventuell auch mit einer regionalen Komponente tektonischer Subsidenz verbunden, zeitgleich mit schneller Subsidenz in der Nordsee. Der 3D- Modellierungsansatz wurde genutzt, um die Salzverteilung für verschiedenen Paläolevels als Reaktion auf Entlastung durch sequentielles Entfernen der stratigraphischen Schichten zu bestimmen. Mit dem Modellierungsansatz wurde auch versucht, die ursprüngliche permische Salzverteilung unmittelbar nach der Ablagerung zu rekonstruieren. Die ursprüngliche Salzmächtigkeit variiert zwischen 1300 m an den Beckenflanken und bis zu 3000 m innerhalb des zentralen Teils und zeigt einen klaren NNO-SSW-Trend innerhalb des Beckens. Die Bildung des tiefen zentraltriassischen Grabens und der nachfolgenden jurassisch- känozoischen Randtröge wurde stark durch die langandauernde Entwicklung von Salzstrukturen kontrolliert. Es wird gezeigt, dass das Sedimentationszentrum sich vom Zentralteil der ursprünglichen Grabenstruktur in Richtung ihrer Ränder verlagerte. Die Auswertung der verfügbaren Daten und die Ergebnisse der 3D-Rückwärtsmodellierung zeigen, dass der größte Teil der Subsidenz nahe aktiver Salzstrukturen auftrat, und eventuell zu einer graduellen Abwanderung permischer Salze führte. Daher zeigt die Studie, dass die Ursache der langzeitigen Subsidenz die graduelle Abwanderung permischen Salzes ist, welche im axialen Teil des Beckens begann und sich im Laufe der Zeit in Richtung der Beckenflanken bewegte. In diesem Sinne wurde der Glückstadtgraben zumindest teilweise in nachpermischer Zeit als basin-scale rim syncline geformt. Daher zeigen die Ergebnisse, dass dieser Salzrückzug während der meso-känozoischen Evolution eine bedeutende Rolle gespielt haben dürfte, und dass die Effekte salzgesteuerter Subsidenz während des Meso-Känozoikums als Hauptursache der Bildung des tiefen zentraltriassischen Grabens und die nachfolgenden jurasso- känozoischen Tröge angesehen werden kann.