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  • 1
    Publication Date: 2009-04-01
    Description: An unsolved problem of regional importance for both the evolution and structure of the Northwest German Basin is the existence or non-existence of the so-called Bramsche Massif. Explaining the nature of this massif and the cause of a related strong, positive Bouguer anomaly (Bramsche Anomaly) is critical. In the study described here, we tested an existing “intrusion model” against a newer “inversion model” in the southern Northwest German Basin. In the intrusion model, the strongly-positive Bouguer anomaly represents the gravity effect of an intrusion at depths between 6 and 10 km. More recent interpretations invoke tectonic inversion rather than intrusion to explain increased burial and the low level of hydrocarbon maturity found in boreholes. We tested these different interpretations by constructing 3D forward density models to 15 km depth. The intrusion model was updated and adjusted to incorporate recent data and we also modelled pre-Zechstein structures using different scenarios. The final model has a very good fit between measured and modelled gravity fields. Based on currently available seismic and structural models, as well as borehole density measurements, we show that the positive Bouguer anomaly cannot be modeled without a high-density, intrusive-like body at depth. However, further in-sight into the crustal structures of the Bramsche region requires more detailed investigations. ©2007 Springer-Verlag
    Print ISSN: 1437-3254
    Electronic ISSN: 1437-3262
    Topics: Geosciences
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  • 2
    Publication Date: 2015-03-31
    Description: The North Anatolian fault (NAF) in the Marmara Sea is a significant hazard for the city of Istanbul. The use of paleoseismological data to provide an accurate seismic risk assessment for the area is constrained by the fact that the NAF system is submarine; thus a history of paleoearthquakes can be inferred only by using marine sediment cores. Here, a record of turbidites was obtained in two cores and used to reconstruct the earthquake history along the Çınarcık segment, a main branch of the NAF. Klg04 was collected from a berm north of the fault, and Klg03 was positioned in the Çınarcık basin, south of the fault. The cores were correlated using long‐term geochemical variations in the sediment, and turbidites deposited simultaneously at both sites were then identified. Radionuclide measurements suggest the most recent turbidite was triggered by the 1894 C.E. Mw 7.3 earthquake. We conclude that the turbidites identified at both sites are earthquake generated, based on their particular sedimentological and geochemical signatures; the correlation of turbidites at berm and basin sites; and the match of the most recent turbidite with a nineteenth century historical earthquake. To date older turbidites, we used carbon‐14 and paleomagnetic data to build an OxCal model with a local reservoir correction of 400±50  yr. The Çınarcık segment is found to have ruptured in 1509 C.E., sometime in the fourteenth century, in 989 C.E., and in 740 C.E., with a mean recurrence interval in the range of 256–321 years. Finally, we used the earthquake record obtained to review the rupture history of the adjacent segments over the past 1500 years.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences
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  • 3
    Publication Date: 2017-06-10
    Description: Die hier dargestellten Methoden dienen der drei-dimensionalen, interaktiven Bearbeitung der Potentialfelder Gravimetrie und Magnetik, sowie ihrer Ableitungen (Schwere- und Magnetik-Tensor). Die Methodik ist sowohl für terrestrische, als auch Bohrloch- und Airborne-Verfahren einsetzbar. Um die Mehrdeutigkeit der interaktiven Bearbeitung bei der Vorwärtsrechnung und Inversion der Felder zu minimieren, beziehen die numerischen Verfahren verstärkt eine schnelle Computergraphik ein, sodass die Randbedingungen (meist aus der Reflexionsseismik) für die Berechnungen durch den Anwender stets sichtbar sind. Die Vorwärtsrechnungen basieren auf der Approximation geologischer Strukturen durch Polyeder, die Inversionsrechnungen für Geometrie und Gesteinsparameter (Dichte, remanente und induzierte Gesteinsmagnetisierung) werden mit Hilfe der CMA-ES (covariance-matrix-adoption evolution strategy) durchgeführt. CMA-ES ist die ideale Methode, um stark nicht-lineare und komplexe Probleme der Geophysik zu optimieren. Der Benutzer hat die Möglichkeit, die Inversion visuell zu steuern und zu beeinflussen. Die die Untergrundstrukturen approximierenden Polyeder sind durch konstante Gesteinsparameter charakterisiert; durch die Überlagerung eines Voxelmodells sind auch Strukturen mit hochgradig variabler Gesteinsparameterverteilung darstellbar. In vielen Anwendungen liegen häufig Daten vor, deren Auflösung für eine Potentialfelder-Modellierung nicht unbedingt erforderlich ist: Hier helfen neu entwickelte automatisierte Verfahren der gestalt-erhaltenden Datenreduktion. Für die Visualisierung von Potentialfeldern in Bohrlöchern werden Beispiele für eine nutzerfreundliche Visualisierung gezeigt.
    Description: conference
    Keywords: Gravimetrie, 3D Modelling, Visualisierung, Bohrlochtool
    Language: German
    Type: anthologyArticle , publishedVersion
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  • 4
    Publication Date: 2017-06-10
    Description: Structural analysts are often faced with the problem of identifying prominent structural discontinuities covered by post-tectonic sedimentary or volcanic rocks. Gravity fields are often used to delineate the trace of buried discontinuities but are frequently found to be too crude to localize discontinuities adequately. Here, we introduce the importance of dip curvature of the isostatic residual gravity for identifying upper-crustal discontinuities. The relationship between Bouguer gravity, isostatic residual gravity and its dip curvature, first-order structural elements and distribution of Neogene volcanic rocks was examined in the central Andean plateau, more specifically, the southern Altiplano and the Puna...
    Description: conference
    Keywords: TSX 000 ; TQA 000 ; VAE 811 ; VEX 100 ; Südamerika {Geophysik} ; Gravimetrische Verfahren {Geophysik} ; Alpidische Orogene {Geologie} ; Anden {Geologie} ; Zentralanden ; Erdkruste ; Diskontinuität <Geologie> ; Gravimetrie
    Language: German
    Type: anthologyArticle , publishedVersion
    Format: application/pdf
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  • 5
    Publication Date: 2012-01-27
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    In:  [Talk] In: Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, 18-22.06., Heredia, Costa Rica .
    Publication Date: 2012-01-27
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
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    In:  [Talk] In: LAK 2005: 19th Colloquium on Latin American Earth Sciences, 18.- 20.04, Potsdam, Germany .
    Publication Date: 2012-01-27
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
    Publication Date: 2017-01-04
    Description: Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 100 (2006): 234-249, doi:10.1016/j.marchem.2005.10.014.
    Description: Over the past few decades, the radioisotope pair of 238U/234Th has been widely and increasingly used to describe particle dynamics and particle export fluxes in a variety of aquatic systems. The present paper is one of five review articles dedicated to 234Th. It is focused on the models associated with 234Th whereas the companion papers (same issue) are focused on present and future methodologies and techniques (Rutgers van der Loeff et al.), C/234Th ratios (Buesseler et al.), 234Th speciation (Santschi et al.) and present and future applications of 234Th (Waples et al.). In this paper, we review current 234Th scavenging models and discuss the relative importance of the non steady state and physical terms associated with the most commonly used model to estimate 234Th flux. Based on this discussion we recommend that for future work the use of models should be accompanied by a discussion of the effect that model and data uncertainty have on the model results. We also suggest that future field work incorporate repeat occupations of sample sites on time scales of 1-4 weeks in order to evaluate steady state versus non steady state estimates of 234Th export, especially during high flux events (> ca. 800 dpm m-2 d-1). Finally, knowledge of the physical oceanography of the study area is essential, particularly in ocean margins and in areas of established upwelling (e.g. Equatorial Pacific). These suggestions will greatly enhance the application of 234Th as a tracer of particle dynamics and flux in more complicated regimes.
    Description: This paper grew out of discussion held at the “Future Applications of 234Th in Aquatic Systems” workshop held at Woods Hole Oceanographic Institution in August, 2004 (see: http://www.geol.sc.edu/cbnelson/Thmeeting/). We are grateful to the US National Science Foundation Chemical Oceanography Program (OCE 0354757) for its support of the workshop. We thank the US National Science Foundation, the National Oceanic and Atmospheric Administration and the Belgian Science Policy for their support of many of the field and modeling efforts described in this paper.
    Keywords: Th-234 ; Model ; Scavenging ; Export ; Particle dynamics
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 2096326 bytes
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  • 9
    Publication Date: 2017-12-21
    Description: Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 100 (2006): 190-212, doi:10.1016/j.marchem.2005.10.012.
    Description: The short-lived thorium isotope 234Th (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th in both marine and freshwater systems. The original 234Th method is labour intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of 234Th from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate 234Th analytical technique for a specific aquatic regime and known sampling constraints.
    Description: Individuals and science efforts discussed herein were supported by many national science programs, including the U.S. National Science Foundation and U.S. Department of Energy and the Ministerio de Educación y Ciencia of Spain. The Agency is grateful for the support provided to its Marine Environment Laboratory by the Government of the Principality of Monaco".
    Keywords: Th-234 ; Methodology ; Sampling ; Analytical techniques, ; Export
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: 327450 bytes
    Format: 289061 bytes
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  • 10
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    In:  [Talk] In: AGU 2007 - Fall meeting, 10.- 14.12, San Francisco, USA .
    Publication Date: 2012-01-27
    Type: Conference or Workshop Item , NonPeerReviewed
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