3. Wochenbericht MSM20/2

FS „Maria S. Merian“, MSM 20-­2 17.1.2012 Walvis Bay – 16.2.2012 Recife 3. Wochenbericht (30.1. bis 5.2.

4. Wochenbericht MSM20/2

FS „Maria S. Merian“, MSM 20-­2 17.1.2012 Walvis Bay – 16.2.2012 Recife 4. Wochenbericht (6.2. bis 12.2.

Tectonic Controls on Gas Hydrate Distribution off SW Taiwan

The northern part of the South China Sea is characterized by widespread occurrence of bottom simulating reflectors (BSR) indicating the presence of marine gas hydrate. Because the area covers both a tectonically inactive passive margin and the termination of a subduction zone, the influence of tectonism on the dynamics of gas hydrate systems can be studied in this region. Geophysical data show that there are multiple thrust faults on the active margin while much fewer and smaller faults exist in the passive margin. This tectonic difference matches with a difference in the geophysical characteristics of the gas hydrate systems. High hydrate saturation derived from ocean bottom seismometer data and controlled source electromagnetic data and conspicuous high‐amplitude reflections in P‐Cable 3D seismic data above the BSR are found in the anticlinal ridges of the active margin. In contrast all geophysical evidence for the passive margin points to normal to low hydrate saturations. Geochemical analyses of gas samples collected at seep sites on the active margin show methane with heavy δ13C isotope composition, while gas collected at the passive margin shows light carbon isotope composition. Thus, we interpret the passive margin as a typical gas hydrate province fuelled by biogenic production of methane and the active margin gas hydrate system as a system that is fuelled not only by biogenic gas production but also by additional advection of thermogenic methane from the subduction system

Electrical properties of the mantle upwelling zone beneath a mid-ocean ridge, an application of vertical gradient sounding

grantor: University of TorontoOn mid-ocean ridges, as adjacent plates move apart, the mantle material rises to fill the void created. During its ascent the solidus of the material is crossed and melting occurs. The melt itself is eventually emplaced at the ridge axis producing new oceanic crust. The understanding of the flow of the solid and molten material is hampered by the lack of knowledge of vital model parameters such as the connectivity of the partial melt. Connectivity is related to the permeability in the upwelling region. It therefore controls the migration pattern of the buoyant melt, the flow of the solid phase material, and the mantle upwelling mechanism. Changes in the geometry of the distribution of melt in the solid material have a large impact on the electrical conductivity. I have measured the conductivity of the upwelling region to constrain possible partial melt geometries. I present results of vertical gradient sounding (VGS) experiments on the Endeavour and Explorer ridge, which are part of the Juan de Fuca and its northern extension, the Explorer ridge, respectively. The VGS method is a natural source EM method based entirely on measurements of the magnetic fields. Electrical responses of the 1D layered normal seafloor combined with a 2D region representing the mantle upwelling zone and proposed upwelling mechanisms are derived. A comparison of the synthetic response of a range of models with data measured on the Endeavour segment shows that the conductivity in the upwelling region is very high (in the order of 1 to 5 ohm m depending on the shape of the upwelling region). The results of this experiment suggest that the pore space containing the conductive melt is well connected. The melt must be able to move freely through the upwelling region. The experiments support so called melt migration models. The data measured on the Explorer segment yielded a different conductivity model. The data do not require the presence of a pronounced 2D conductivity anomaly at depth and therefore precludes the existence of large or well connected melt fractions in an upwelling region underneath Explorer ridge. The data therefore support a study of magnetic anomaly maps that suggests that the Explorer ridge is degenerate, i.e. that the Explorer plate is slowly deforming internally and its movement is governed by the movement. of the surrounding plates.Ph.D

Joint inversion of marine magnetotelluric and gravity data incorporating seismic constraints Preliminary results of sub-basalt imaging off the Faroe Shelf

Breakup of the North Atlantic during the early tertiary was accompanied by widespread and massive magmatism, resulting in the coverage of large areas of the North Atlantic with flood basalts. These flood basalts hamper seismic investigations of underlying sequences and thus the understanding of the rifting, subsidence and evolution of the margin which, in turn, increases the risk for hydrocarbon exploration. In this paper we present a methodology for the simultaneous joint inversion of diverse geophysical datasets, i.e. free air gravity and magnetotelluric soundings (MT) using seismic a priori constraints. The attraction of the joint inversion approach is that different geophysical measurements are sensitive to different properties of the sub-surface, so through joint inversion we significantly reduce the null space and produce a single model that fits all datasets within a predefined tolerance. Using sensitivity analysis of synthetic data, we show how each data set contains complementary important information of the supra and sub-basalt structure. While separate inversions of individual datasets fail to image through the basalt layer, our joint inversion approach leads to a much improved sub-basalt structure. Application of the joint inversion algorithm to satellite gravity data and MT data acquired on the FLARE10 seismic line south west of Faroe islands supports the existence of a 1 km to 2 km thick low velocity region that might be indicative of the existence of a sedimentary basin underneath the basalt layer. Though in this paper we demonstrate the use of joint inversion on a sub-basalt target, we believe it has wider applicability to other areas where conventional seismic imaging fails

Point Process Tools

This toolbox implements various tools for working with simple, non-marked, one dimensional point processes. The highlight of this toolbox is the new goodness-of-fit test developed for parametric models

Dynamic controls of fluid and gas flow at North Alex Mud Volcano, West Nile Delta

OS51D-01 The North Alex Mud Volcano (NAMV) is located at a water depth of 500m above a large deep-seated gas reservoir on the upper slope of the western Nile deep-sea fan. It has been the object of an integrated study of fluid and gas flow using existing and newly developed observatory technologies to better constrain and quantify devolatilisation and defluidisation patterns and their long-term variability in relation to underlying hydrocarbon reservoirs. As it is known that the activity of mud volcanoes varies significantly over periods of months and weeks, the assessment of the activity of NAMV focuses on proxies of fluid and gas emanations. Submarine mud volcanoes are usually characterized by fluid formation and fluidization processes occuring at depths of several kilometers below the seafloor, driving a complex system of interacting geochemical, geological and microbial processes. Mud volcanoes are natural leakages of oil and gas reservoirs. Near-surface observations made at such sites can therefore be used to monitor phenomena that occur at greater depth. Since the initiation of the project in 2007, NAMV has arguably become one of the best-instrumented mud volcanoes worldwide with a network of observatories collecting long-term records of chemical fluxes, seismicity, temperature, ground deformation, and methane concentration. In addition five research cruises collected complementary geophysical and geological data and samples. In the summer of 2010 a large number of monitoring systems has been recovered which provide us with a synoptic view of the internal dynamics of an active mud volcano. We will present an integrated analysis based on ship-based and sea-floor observations