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  • 1
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    In:  [Poster] In: Taiwanese-German Joint Symposium on Marine Gas Hydrate: TaiGer VIII , 05.-06.04.2018, Bremen, Germany .
    Publication Date: 2018-05-24
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 2
    Publication Date: 2019-02-01
    Description: We present high-resolution resistivity imaging of gas hydrate pipe-like structures, as derived from marine controlled-source electromagnetic (CSEM) inversions that combine towed and ocean-bottom electric field receiver data, acquired from the Nyegga region, offshore Norway. Two-dimensional CSEM inversions applied to the towed receiver data detected four new prominent vertical resistive features that are likely gas hydrate structures, located in proximity to a major gas hydrate pipe-like structure, known as the CNE03 pockmark. The resistivity model resulting from the CSEM data inversion resolved the CNE03 hydrate structure in high resolution, as inferred by comparison to seismically constrained inversions. Our results indicate that shallow gas hydrate vertical features can be delineated effectively by inverting both ocean-bottom and towed receiver CSEM data simultaneously. The approach applied here can be utilised to map and monitor seafloor mineralisation, freshwater reservoirs, CO2 sequestration sites and near-surface geothermal systems.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2018-09-12
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
    Publication Date: 2019-01-11
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  • 5
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    In:  [Talk] In: Schmucker-Weidelt-Kolloquium - 24. Kolloquium Elektromagnetische Tiefenforschung, 26.09.-29.09.2011, Neustadt an der Weinstraße .
    Publication Date: 2012-02-23
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  • 6
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    Copernicus Publications (EGU)
    In:  [Poster] In: EGU General Assembly 2011, 03.04.-08.04.2011, Vienna, Austria .
    Publication Date: 2012-07-06
    Description: Even though first experiments for the characterization of the seafloor using marine electromagnetic (EM) methods were already carried out in the mid 1960’s, they have only played a minute role in marine academic investigation for several decades. Only in the past decade, the strongly increasing interest of oil companies for alternative investigation methods for marine oil and gas exploration brought the use of EM methods into the focus of attention. Traditional founders of marine EM methods (Scripps, U of Toronto, U of Southampton) are now accompanied by newly established commercial (e.g. Exxon, AOA Geophysics, OHM surveys, EMGS, Statoil) as well as academic groups. The marine EM group at the IFM GEOMAR, which was established in 2006, initially focused on the development and testing of EM receivers (RX) for magnetotelluric (MT) measurements. Successful measurements were taken during a cruise to the Costa Rican trench (2007/08, see Worzewski, this session). However, these measurements revealed some problems with this first generation of instruments (e.g. stability of stations on the ocean-floor). A subsequent, much improved generation of MT receivers developed in 2008 was successfully deployed during cruises to the Alboran Sea (2009) and the Cyprus Arc (2010) and is currently used in investigations of the Walvis Ridge (Namibia, 2011) and the New Zealand Subduction Zone (2011). For a RWE Dea funded project at the North Alex Mud Volcano (NAMV), a second line of development at the IFM-GEOMAR focused on development of controlled source electromagnetic (CSEM) equipment. For this first project, safety concerns (slop stability) as well as the comparatively small size of the investigated target ([ca.] 1km2) required a new approach to allow for a secure, high resolution CSEM experiment. For this type of experiment, the existing MT receivers were extended to include a high frequency CSEM mode (10kHz) for the electric fields. Additionally, a lightweight electric dipole transmitter (TX), which can be mounted on a small remotely operated underwater vehicle (ROV) was developed. In a 3D-style tomographic experiment (Nov. 2008), ten receivers were deployed over the surface of NAMV at a total of 16 receiver locations and in three successful dives with a Cherokee ROV (Ghent University, Belgium), the transmitter was deployed at a total of 80 locations. Since both RXs and TX were stationary during measurements, a small dipole moment of 200Am (20A current, 10m dipole length) was sufficient to collect transient data up to RX-TX distances of more than 1km. Generally, navigational inaccuracy limits the accuracy and thus also the resolution of CSEM measurements, which is mainly due to the constantly moving sources used in most commercial systems. The good quality of data recorded during the initial experiment at the NAMV raises the question, if this issue may for some types of CSEM experiments may be remedied by using stationary transmitters instead of flying sources. During the upcoming experiment in New Zealand (April 2011), we will find some answers to this question with our new CSEM transmitter system, which has a higher dipole moment ([ca.] 1kAm) and the capability to perform the navigation between TX and the RXs directly on the ocean floor.
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  • 7
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    Society of Exploration Geophysicists
    In:  Geophysics, 77 (3). E171-184.
    Publication Date: 2018-06-08
    Description: Electromagnetic methods are commonly employed in exploration for land-based mineral deposits. A suite of airborne, land, and borehole electromagnetic techniques consisting of different coil and dipole configurations have been developed over the last few decades for this purpose. In contrast, although the commercial value of marine mineral deposits has been recognized for decades, the development of suitable marine electromagnetic methods for mineral exploration at sea is still in its infancy. One particularly interesting electromagnetic method, which could be used to image a mineral deposit on the ocean floor, is the central loop configuration. Central loop systems consist of concentric transmitting and receiving loops of wire. While these types of systems are frequently used in land-based or airborne surveys, to our knowledge neither system has been used for marine mineral exploration. The advantages of using central loop systems at sea are twofold: (1) simplified navigation, because the transmitter and receiver are concentric, and (2) simplified operation because only one compact unit must be deployed. We produced layered seafloor type curves for two particular types of central loop methods: the in-loop and coincident loop configurations. In particular, we consider models inspired by real marine mineral exploration scenarios consisting of overburdens 0 to 5 m thick overlying a conductive ore body 5 to 30 m thick. Modeling and resolution analyses showed that, using a 50 m(2) transmitting loop with 20 A of current, these two configurations are useful tools to determine the overburden depth to a conductive ore deposit and its thickness. In the most extreme case, absolute voltage errors on the order of 10 nV are required to resolve the base of a 30 m thick ore deposit. Whether such noise floors can be achieved in real marine environments remains to be seen.
    Type: Article , PeerReviewed
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  • 8
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    In:  [Poster] In: 9th International Conference on Gas in Marine Sediments (ICSG), 15.-19.09.2008, Bremen .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
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    In:  [Other] In: 69. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG), 23.03.-26.03.2009, Kiel . 69. Jahrestagung der Deutschen Geophysikalischen Gesellschaft in Kiel : 23.-26. März 2009 ; p. 22 .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
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    Geological Society Publ. House
    In:  In: Growth and Collapse of the Tibetan Plateau. , ed. by Gloaguen, R. and Ratschbacher, L. GSL Special Publications . Geological Society Publ. House, Bath, UK, pp. 221-233. ISBN 978-1-86239-326-4
    Publication Date: 2017-05-23
    Description: The endorheic Gaxun Nur Basin (GNB, local name: Ejina basin), which is located north of the Tibetan Plateau between the tectonic stress fields of the Qilian Shan and the Gobi-Tienshan, has evolved as a large inland basin filled with deltaic sediments during the past 250 ka. Here we present selected examples of geomorphological, sedimentological and geophysical evidence of tectonic activity and discuss a possible time frame of selected occurrences. We used medium-scale geomorphological mapping supported by analyses of Landsat ETM images, Corona images and an Aster Digital Terrain Model (Aster-DTM), combined with field surveys, dated sediment sections, and geophysical investigations using electromagnetic methods. The spatio-temporal distribution of radiocarbon-dated lake sediments within the northern GNB indicates a non-even distribution of neotectonic activity with west–east increasing amplitude of subsidence rates from 0.8–1.1 m/ka in the western part and more than three times higher rates in the eastern part. Our data indicate that tectonic has strongly amplified climate-induced environmental changes and may be regarded as an example of non-climatic pulses affecting lake-hydrology and basin development.
    Type: Book chapter , NonPeerReviewed
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