229 documents found in 225ms
# 1
Dias, N.A. • Silveira, G. • Haberland, C.
Abstract: The lithosphere of Iberia has been formed through a number of processes of continental collision and extension. In Lower Paleozoic, the collision of three tectonics blocks produced the Variscan Orogeny, the main event of formation of the Iberian lithosphere. The subsequent Mesozoic rifting and breakup of the Pangea had a profound effect on the continental crust of the western border of Iberia. Since the Miocene, the southern interaction between Africa and Iberia is characterized by a diffuse convergent margin that originates a vast area of deformation. The impact of this complex tectonic in the structure of the Iberian Lithosphere remains an incognito, especially in its western part beneath Portugal. While the surface geology is considerably studied and documented, the crustal and lithospheric structures are not well constrained. The existing knowledge relating the observed surface geology and Lithospheric deep structures is sparse and sometimes incoherent. The seismic activity observed along West Iberia is intensely clustered on few areas, namely on north Alentejo, Estremadura and Regua-Verin fault systems. Some of the problems to address are: What is the relation between surface topography and the deep crustal/lithospheric structure? How was it influenced by the past tectonic events? Which was the deep driving factor behind the tectonic units observed at surface: Lithosphere-Astenosphere boundary structure or deeper mantle structure? How the upper mantle and the Lithosphere-Astenosphere transition zone accommodated the past subduction? Which is its role and influence of the several tectonic units, and their contacts, in the present tectonic regime and in the stress field observed today? Is the anomalous seismicity and associated crustal deformation rates, due to an inherited structure from past orogenies? The main goal of this work is a 3D detailed image of the “slice” of the Earth beneath Western Iberia, by complementing the permanent seismic networks operating in Portugal and Spain. The different scales involved require the usage of several passive seismological methods: Local-Earthquake Tomography for fine structure of seismogenic areas, ambient noise tomography for regional crustal structure, Receiver Functions for Lithospheric structure and Surface-wave tomography for large scale Listosphere-Astenosphere structure. Crustal and Mantle seismic anisotropy analysis, coupled with source analysis and correlation with current geodetic measurements will allow establishing a reference 3D anisotropy model of present and past processes.
# 2
Balling, Niels • Tilmann, Frederik • Kind, Rainer
Abstract: This project investigates the crust and upper mantle along a north-south oriented, about 350 km long profile from around the town of Ringkøbing in western Jutland to south of Hamburg in northwestern Germany, with a focus on teleseismic receiver functions and seismic tomography. A number of tectonic processes have affected the crust and uppermost mantle beneath southern Scandinavia and northern Germany: Precambrian crustal accretion in southern Baltica, Caledonian collision between Baltica and Avalonia along the Tornquist Suture Zone (TSZ), followed by Variscan collision and formation of the North German and the Norwegian-Danish basins, and more recent magmatic activity to the south. This study is particularly focused on the closure of the Tornquist Sea and the Caledonian collision between Baltica and Avalonia. A total of 29 stations, provided by GFZ and the University of Aarhus, were deployed between autumn 2010 and summer 2012, of which 25 form the main profile, and 4 are positioned in an off-line location. Waveform data are available from the GEOFON data centre, under network code ZW, and are available under CC-BY 4.0 license according to GIPP-rules.
# 3
Heit, Ben • Yuan, Xiaohui • Jokat, Wilfried • Weber, Michael • Geissler, Wolfram
Abstract: The Etendeka continental flood-basalt province in northern Namibia, linked by the Walvis Ridge to the Tristan da Cunha hotspot, has great importance in global plate tectonic concepts, and is an ideal place to understand the role of the plume-lithosphere interaction during the break-up of the Southern Atlantic Ocean. Within this frame we operated an amphibian passive-source seismic network (WALPASS for Walvis Ridge Passive Source Experiment) in the region where the Walvis Ridge intersects with the continental margin of northern Namibia. The land network operated for over two years while the OBS stations were in operation for one year. The broadband seismic network is composed of 28 three-component land stations and 12 ocean-bottom stations. This configuration of stations will allow us to map the lithospheric and upper mantle structure in the ocean-continent transition beneath the passive continental margin of northern Namibia and to examine possible seismic anomalies related to the postulated hotspot track from the continent to the ocean along the Walvis Ridge. The acquired data should help clarify the velocity anomaly in the lowermost mantle caused by the Africa super plume and to improve the distribution of seismicity in this geophysically little studied region.
# 4
Heit, Benjamin • Yuan, Xiaohui • Mancilla, Flor de Lis
Abstract: We operated a densely spaced broadband seismic field experiment to study the structure of the crust and mantle lithosphere across the Sierra Nevada mountain range, southern Spain. The Sierra Nevada is one of the key areas within the complicated Betic-Alboran-Rif system. It contains the highest mountain of the Iberian Peninsula and is located in the close vicinity of a very deep seismic zone (>600 km depth). This region plays a decisive role in answering the question if subduction or delamination is the dominant geological process in the western Mediterranean. The seismic array, consisting of 40 broadband stations spaced 2 km apart (compared to earlier station spacing of ~50 km), has been deployed in September 2010 by a joint effort of GFZ Potsdam and University of Granada, and has been operated until the end of 2011. The proposed scientific work is the analysis of the data collected with the present experiment which includes mainly P and S receiver function analysis and surface wave tomography with ambient noise data. We will image the seismic structure and thickness variation of the crust and mantle lithosphere at high resolution and hence infer tectonic and geodynamic processes related to the Africa-Eurasia collision. The resulting structural details especially of the mantle lithosphere will contribute essentially to the recognition of the geodynamic deformations in the western part of the African-Eurasian plate collision. Data are available from the GFZ seismological data archive.
# 5
geofon operator
Abstract: Earthquake, 2010-02-26 20:31:25, Ryukyu Islands, Japan
# 6
geofon operator
Abstract: Earthquake, 2010-04-06 22:15:02, Northern Sumatra, Indonesia
# 7
KTB, WG Geochemistry
Abstract: The qualitative and quantitative phase analyses were performed in the KTB field laboratory by x-ray powder diffraction using SIEMENS D 500 diffractometer. During early stages of the KTB project a new method for quantitative phase analysis was developed (see references below). The method is based on the comparison of the diffraction spectrum of the unknown sample with those of pure minerals. The powder diffraction data of the minerals are stored in a database built up of 250 natural minerals separated from various types of igneous and metamorphic rocks. The complete analyses (radiation: Cu K alpha, lambda: 1,5405Å, stepwidth: 0,01°, counting time 2 sec/step, angle 2-80°) was carried out automatically including computations. The results of this quantitative phase analysis were used e.g. to check thin section petrography (and vice versa) and to construct a \"mineralogical rock composition log\".
# 8
KTB, WG Geophysics
Abstract: In the laboratory, the gamma radiation is measured by a sodium iodtite (NaI) scintillation detector (cores and cuttings) and by a germanium (Ge) semiconductor detector (cuttings). The cuttings are measured in air tight Marinelli-beakers with a volume of 250 cm3. For the core measurements a special, automatically operating equipment with three NaI detectors is used. A description of this apparatus is given in Wienand et al. (1989). The principle of measurements with the Ge-detector is described by Bücker et al. (1991).The measured spectra are calibrated by a standard of Luvarovite (NIM-L, South African Bureau of Standards). The influence of the local terrestrial radiation on the measurements has been corrected. Especially for the core measurements a calibration procedure has been performed for geometric corrections (core diameter and length). In general, a measuring time of 12 h for the NaI-detector and 2 h for the Ge-detector was chosen.
# 9
KTB, WG Geophysics
Abstract: The thermal conductivity on cores is measured in two steps (see Pribnow 1994). First, one face end of the core is sawed and polished. The half space line source is pressed against this preparated face (without further contact medium like water) by a computerized device. The position of the heat source is varied in 15 degree intervals around one semicircle. At each position, 3 repeating measurements are performed. The line source azimuth of the lowest measured thermal conductivity is the strike of the foliation plane. On the other hand, the thermal conductivity is maximal parallel to that direction. This apparent paradox can be explained by the experimental method, because the measurement plane is perpendicular to the orientation of the line source (Pribnow 1994).In a second step a calotte plane perpendicular to the strike of foliation is prepared. A second series of thermal conductivity measurements in 15 degree intervals ...
# 10
KTB, WG Geochemistry
Abstract: Geochemical Analysis of Anions of Mud Samples of the KTB Main Hole HB1h.
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