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  • 1
    Call number: 4/M 05.0119
    Type of Medium: Monograph available for loan
    Pages: XIV, 130 S.
    Edition: 3. veränd. Aufl.
    Location: Reading room
    Branch Library: GFZ Library
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  • 2
    Publication Date: 2007-12-12
    Description: The island of Crete represents a horst structure located in the central forearc of the retreating Hellenic subduction zone. The structure and dynamics of the plate boundary in the area of Crete are investigated by receiver function, surface wave and microseismicity using temporary seismic networks. Here the results are summarized and implications for geodynamic models are discussed. The oceanic Moho of the subducted African plate is situated at a depth of about 5060 km beneath Crete. The continental crust of the overriding Aegean lithosphere is about 35 km thick in eastern and central Crete, and typical crustal velocities are observed down to the upper surface of the downgoing slab beneath western Crete. A negative phase at about 4 s in receiver functions occurring in stripes parallel to the trend of the island points to low-velocity slices within the Aegean lithosphere. Interplate seismicity is spread out about 100 km updip from the southern coastline of Crete. To the south of western Crete, this seismically active zone corresponds to the inferred rupture plane of the magnitude 8 earthquake of AD 365. In contrast, interplate motion appears to be largely aseismic beneath the island. The coastline of Crete mimics the shape of a microseismically quiet realm in the Aegean lithosphere at 2040 km depth, suggesting a relation between active processes at this depth range and uplift. The peculiar properties of the lithosphere and the plate interface beneath Crete are tentatively attributed to extrusion of material from a subduction channel, driving differential uplift of the island by several kilometres since about 4 Ma.
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  • 3
    Publication Date: 1999
    Keywords: KTB, ISO 89, Oberpfalz, reflection seismics, seismic processing/methodology
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  • 4
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    Inst. f. Geophys., Ruhr-Univ. Bochum
    In:  Wissenschaftliche Veröffentlichungen, Reihe B, Arlington, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. E35, no. 31, pp. 1-13, pp. B04310, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1989
    Keywords: Seismology ; Induced seismicity ; Rock bursts (see also ERDSTOSS and GEBIRGSSCHLAG) ; GEBIRGSSCHLAG (see also rockburst and Erdstoss) ; Earthquake catalog
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  • 5
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The Ocean Drilling Program (ODP), and its predecessor DSDP, collected a unique data set which can be used to verify fundamental hypotheses on the origin and constitution of the oceanic crust. The combination of geophysical surface- and boreholemeasurements with geological and petrological probing requires a multidisciplinary approach. In this respect, the purpose of this paper is to show the possibilities of reflection seismic data to support stratigraphic interpretation. The data used in this investigation come from one of the prime targets of German ODP-research, namely the Moroccan basin offshore NW-Africa. Drill Site 416 and two multichannel seismic profiles were at our disposal. The punctuate information on physical rock properties and logging results at Site 416 were processed to appear comparable with the seismic profiles. Computation of synthetic seismograms using borehole data as input (forward modelling) allowed to associate reflection horizons with geological boundaries. Calculation of pseudo-velocity logs from reflection profiles (inverse modelling), calibrated by the borehole measurements, enables us to extend the local information of the drill site into a wider area. Although reconnaissance surveys within ODP-programs do not produce a data set comparable in quantity and quality with commercial seismic exploration campaigns, they present an excellent opportunity to use quantitative modelling techniques to understand the origin of the seismic record in a specific region and to examine the potential of seismic stratigraphy as an important tool in marine geosciences.
    Abstract: Résumé L' «Ocean Drilling Program» (ODP), comme son prédécesseur le DSDP, a récolté un ensemble unique de renseignements utilisables à la vérification des hypothèses fondamentales relatives à l'origine et à la constitution de la croûte océanique. La combinaison des mesures géophysiques, effectuées en surface et en sondage, avec les données géologiques et pétrologiques exige une approche pluridisciplinaire. A cet égard, l'objet de cette note est de montrer l'apport de la sismique — réflexion dans l'interprétation stratigraphique. Les données utilisées proviennent d'une des premières cibles du programme allemand ODP, à savoir le bassin marocain situé au large du NW de l'Afrique. Nous avons eu à notre disposition le sondage n∘ 416, ainsi que deux profils sismiques multicanaux. Les informations ponctuelles sur les propriétés physiques des roches et les mesures effectuées dans le sondage 416 ont été traitées de manière à être comparables aux profils sismiques. Des séismogrammes synthétiques ont été calculés à partir des mesures faites dans le sondage (modélisation directe), ce qui a permis de corréler les réflecteurs avec les limites géologiques. Le calcul, à partir des profils «réflexion», de logs de pseudo-vitesse (modélisation inverse) calibrés par les mesures faites dans le sondage nous a permis d'étendre les informations locales fournies par le sondage à une aire plus étendue. Bien que les levés de reconnaissance que comporte le programme ODP ne fournissent pas un ensemble de données comparables en qualité et en quantité à celles d'une campagne d'exploration sismique commerciale, ils procurent néanmoins une excellente occasion d'appliquer les techniques de la modélisation quantitative à l'interprétation des enregistrements sismiques et de montrer les possibilités de l'outil important que constitue la stratigraphie sismique dans la géologie sous-marine.
    Notes: Zusammenfassung Das Ocean Drilling Project (ODP, früher DSDP) liefert einen einmaligen Datensatz, der für die Verifizierung von fundamentalen Hypothesen zur Entstehung und Zusammensetzung der ozeanischen Kruste dienen kann. Die Kombination von geophysikalischen Oberflächenund Bohrlochmessungen erfordert zusammen mit den geologischen und petrologischen Daten einen interdisziplinären Ansatz. In dieser Hinsicht möchte der folgende Artikel die Möglichkeiten aufzeigen, die seismische Daten für die Unterstützung einer stratigraphischen Interpretation bieten. Die Daten dieser Untersuchung stammen aus einem Hauptzielgebiet der deutschen ODP-Forschung, dem marokkanischen Becken westlich der NW-Küste Afrikas. Die DSDP-Bohrlokation 416 und zwei seismische Mehrkanal-Profile standen uns zur Verfügung. Die punktuelle Information über die physikalischen Gesteinseigenschaften und die Ergebnisse der Bohrlochmessungen des Site 416 wurden so bearbeitet, daß sie mit den seismischen Profilen vergleichbar sind. Die Berechnungen von synthetischen Seismogrammen mit den Bohrlochmessungen als Eingangsdaten (Vorwärtsmodellierung) erlaubt die Verbindung von Reflexionshorizonten mit geologischen Grenzen. Die Berechnung von Pseudo-Geschwindigkeitslogs, kalibriert an den Bohrlochmessungen, aus den reflexionsseismischen Profilen (inverses Modellieren), ermöglicht es, die lokale Information des Bohrlochs über einen größeren Bereich um das Bohrloch zu erweitern. Obwohl die Vorerkundungsarbeiten innerhalb des ODP-Projekts Daten erbringen, die in Quantität und Qualität nur eingeschränkt mit denen kommerzieller seismischer Explorationserkundungen vergleichbar sind, stellen sie eine hervorragende Möglichkeit zur Anwendung von quantitativen Modellierungstechniken dar, die zur Interpretation der Seismogramme der untersuchten Region beitragen und die Leistungsfähigkeit der seismischen Stratigraphie als ein wichtiges Werkzeug in den marinen Geowissenschaften zeigen.
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
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  • 7
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    Deutsches GeoForschungsZentrum GFZ
    Publication Date: 2016-05-13
    Description: Abstract
    Description: Data acquisition from 1996-2002 was divided into five separate field deployments: one in 1996 and 1997 in western Crete, one in 1999 on the small island Gavdos, south of Crete, one in 2000/2001 in the Messara plain in central Crete and finally one in 2002 in the gap between the western and central Crete networks south of Rethimnon. For all deployments, short period seismometers (Mark-L4-3D, S13, GS13 or CM-3) and PDAS100 dataloggers were used. In 1996 a network of six mini-arrays was installed on westen Crete. Each mini-array consist of a central three-component seismometer (A01-A06) surrounded by three vertical component seismometers (A110,A120,A130,A210,..) within a radius of about 300 m. The average distance between the cental stations was about 10 km. These central stations were re-used in 1997 and the network was extended to 47 stations (A001-A047) equipped with tree-component seismometers deployed all over western Crete except the Levka Ori. Although the network aperture was significantly increased from about 20 km to 60 km the station spacing was reduced to 5 km. 12 stations (GA01-GC03) were installed on Gavdos in 1999 with a network aperture of only 5 km limited to the size of the island. The dense spacing allows array methods for the detection and localisation of seismicity. In 2000/2001 an 8 station network (M001-M008) was located around the Messara plain in central Crete. The maximum aperture of this network was 50 km in EW and 20 km in NS direction. To close the gap in the seismicity observation between western and central Crete 7 stations (R01-R07) were installed south of Rethimnon in 2002. The seismic networks were originally planned as part of pre-site surveys for specific drilling proposals within the International Continental Drilling Program (ICDP). The networks provide the opportunity to image shallow seismically active zones of the Hellenic subduction zone. Waveform data is available from the GEOFON data centre, under network code YU, and is fully open.
    Keywords: Seismic waveforms Crete ; Seismic monitoring ; Monitoring system ; Seismological stations
    Type: Other , Seismic Network
    Format: Greater than 150 GB
    Format: SEED data
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  • 8
    Publication Date: 2016-05-13
    Description: Abstract
    Description: The focus of the two temporary seismic networks CYCNET and LIBNET was to monitor the south Aegean region which has the highest seismic activity in Europe. The knowledge of seismotectonics of the volcanic arc of the Hellenic subduction zone poses a number of questions that can best be addressed via an investigation of the spatiotemporal distribution of hypocenters. In order to obtain hypocenters with small location errors and low detection threshold the CYClades seismic NETwork (CYCNET) was installed in the central volcanic arc of the Hellenic subduction zone. Up to 22 stations, equipped with short-period and broadband sensors, were distributed on 17 islands and operating for more than two years starting in autumn 2002. Most islands were equipped with a single seismic station. To decrease the detection threshold at the volcanic centers of Milos and Santorini additional stations were installed there. The combination of short-period and broadband sensors provides data for both seismicity studies and structural investigations. Focussing on the Santorini-Amorgos zone the University of Hamburg (Dahm, T., Hensch, M.) deployed 6 Ocean Bottom Seismometers (OBS)(SANT1-SANT6) near the submarine volcano Columbo for about two month in 2005. In order to better resolve seismic activity in the region of the forearc slivers between the Ptolemy-, Pliny- and Strabo-Trenches south of Crete and to map the subducting African lithosphere in this region as well as the southern termination of the seismogenic zone the LIByan sea the seismic offshore NETwork (LIBNET) was installed. This network consisting of up to 6 simultaneously recording Ocean Bottom Seismometers (OBS) was operated from May 2003 until June 2004 in five subsequent deployment phases. Waveform data are available from the GEOFON data centre, under network code ZZ, and are fully open.
    Keywords: Seismic waveforms Cyclades ; Seismic monitoring ; Monitoring system ; Seismological stations
    Type: Other , Seismic Network
    Format: Approx. 600 GB
    Format: SEED data
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  • 9
    ISSN: 1420-9136
    Keywords: Key words: Borehole seismics, velocity estimation, KTB seismic experiments, vertical receiver array, transmitted wave field, P-to-S conversion.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Within the "Integrated Seismics Oberpfalz 1989 (ISO89)" a three-component Moving Source Profiling (MSP) experiment, also named walk-away VSP, was carried out at the drilling site of the "Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland (KTB)" in Germany. Analysis of transmitted waves traveling from the source locations at the surface down to the receiver array in the borehole reveals velocity information about the illuminated part of the subsurface. Complementary to the widely used evaluation of travel-time perturbations to locate velocity inhomogeneities we suggest the use of the directivity of transmitted wave types down in the borehole. To determine the wave-field directivity we focus on transmitted arrivals by employing principles of "Controlled Directional Reception (CDR)." We calculate local slant-stacks for three different depth positions as a function of the source offset, thus obtaining the variation of the vertical slowness (vertical ray parameter) of incident waves along the horizontal source profile and the vertical receiver array. The slowness data combined with travel times are interpreted by forward modeling taking into account geological information of the survey area. Our findings confirm results from gravity measurements which suggest the existence of large amphibolite/metabasite complexes in the vicinity of the borehole. The described method is also used to identify P-to-S converted energy originating from fracture zones above the receiver array and to locate the region in which conversion occurs.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2017-05-05
    Description: On a SW–NE profile from the Libyan coast towards central Turkey phase velocity curves of the fundamental Rayleigh mode were measured using a two-station method. The inversion of phase velocity curves yields 1-D models of shear wave velocity down to approximately 200 km depths that may be interpreted as estimates of average models between neighbouring stations on the profile. Strong lateral variations in the shear wave velocity structure are imaged along the profile. The subducted oceanic African mantle lithosphere is indicated in 1-D models for the region around Crete by significantly enlarged shear wave velocities. It is also imaged by an average model of the structure between stations on Crete and Santorini. On a path crossing the Libyan Sea south of Crete the resulting model is slower than a model expected for 110 Myr old oceanic lithosphere. The passive African margin is thus assumed to extend northwards beneath the Libyan Sea. Anomalous low shear wave velocities are found for the uppermost mantle beneath central Turkey down to a depth of approximately 130 km. Using two stations on Crete the average depth of the oceanic Moho within the subducting slab is estimated to be at approximately 50 km beneath Crete. For this arc-parallel path, an enlarged standard deviation of the measured phase velocities of approximately 0.2 km s−1 between 10 and 30 mHz is observed that is probably caused by strong lateral heterogeneity related to the subducting slab. In addition, in this frequency range an anomalous propagation of the fundamental Rayleigh mode is detected that is indicated by measured phase velocities that are approximately one standard deviation faster than phase velocities expected from a great-circle approximation. An average shear wave velocity of approximately 3.5 km s−1 is observed above the oceanic Moho. In order to explain the recent lithospheric structure of the Hellenic subduction zone a tectonic model is assumed for the NE–SW striking profile considered. It is based on the calculated 1-D models, tectonic reconstructions and on a model derived from the metamorphic history of rocks exposed on Crete. The suggested model summarizes the tectonic development at a lithospheric scale starting in the Late Cretaceous. Accretion of crustal material of two microcontinents to Eurasia is assumed, while continuous subduction of the oceanic lithosphere of different ocean basins and possibly of the mantle lithosphere of the microcontinents resulted in a single slab. The length of the oceanic lithosphere that was subducted south of Crete is estimated to be not greater than approximately 550 km.
    Type: Article , PeerReviewed
    Format: text
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