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  • AGU (American Geophysical Union)  (29)
  • Wiley  (16)
  • Kiel : GEOMAR, Forschungszentrum für Marine Geowissenschaften an der Christian-Albrechts-Universität zu Kiel  (3)
  • IFM-Geomar, Kiel  (2)
  • 1
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: Online-Ressource ([14] p. = 61,0 KB)
    Edition: [Elektronische Ressource]
    Language: German , English
    Note: Contract BMBF 03G144 A. - Differences between the printed and electronic version of the document are possible. - nBibliography p. [8] - [10] , Also available as printed version , Systemvoraussetzungen: Acrobat Reader.
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  • 2
    Keywords: Forschungsbericht
    Description / Table of Contents: Hot spot volcanism, Musicians Seamounts, Italian Ridge, Bach Ridge, Crustal Structure, Ocean bottom hydrophones
    Type of Medium: Online Resource
    Pages: Online-Ressource ([10] p. = 57,6 KB)
    Edition: [Elektronische Ressource]
    Language: German , English
    Note: Contract BMBF 03G142A. - Differences between the printed and electronic version of the document are possible. - Engl. abstract under title: SO 142-HULA II: Interdisciplinary investigations on the timing of the Hawaii-emperor bend and the origin of lithospheric anomalies along the musician seamount chain. - nBibliography p. [5] - [6]. - nIndex p. 7 , Also available as printed version , Systemvoraussetzungen: Acrobat Reader.
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  • 3
    Keywords: Forschungsbericht
    Description / Table of Contents: Galápagos Islands, East Pacific, hotspot, plume-ridge interaction, geochemistry, volcanology, magnetic anomalies, morphology
    Type of Medium: Book
    Pages: Getr. Zählung, [296] S. , Ill., graph. Darst., Kt.
    Language: English , German
    Note: Förderkennzeichen BMBF 03 G 144 A , Text teils dt., überw. in engl. Sprache , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden , Teilweise auch als elektronische Ressource vorh
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  • 4
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    IFM-Geomar, Kiel
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551.4 ; 551.22 ; 550
    Language: English
    Type: article , publishedVersion
    Format: 193 S.
    Format: application/pdf
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  • 5
    Publication Date: 2021-03-29
    Description: report
    Keywords: 551.4 ; 551.22 ; 550 ; UKD 100 ; TSZ 200 ; TSJ 200 ; TOH 300 ; TOH 100 ; TOH 200 ; TQC 600 ; Expeditionsberichte {Regionale Ozeanologie, Indischer Ozean} ; Indischer Ozean {Geophysik} ; Südostasien {Geophysik} ; Seismische Wellen {Geophysik} ; Seismometrie {Geophysik} ; Seismische Vorhersagen {Geophysik} ; Tiefseeseismik {Geophysik}
    Language: English
    Type: article , publishedVersion
    Format: 212 S.
    Format: application/pdf
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  • 6
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 94 (B11). pp. 16023-16035.
    Publication Date: 2018-03-06
    Description: A seismic refraction profile recorded along the geologic strike of the Chugach Mountains in southern Alaska shows three upper crustal high-velocity layers (6.9, 7.2, and 7.6 km/s) and a unique pattern of strongly focussed echelon arrivals to a distance of 225 km. The group velocity of the ensemble of echelon arrivals is 6.4 km/s. Modeling of this profile with the reflectivity method reveals that the echelon pattern is due to peg-leg multiples generated from with a low-velocity zone between the second and third upper crustal high-velocity layers. The third high-velocity layer (7.6 km/s) is underlain at 18 km depth by a pronounced low-velocity zone that produces a seismic shadow wherein zone peg-leg multiples are seen as echelon arrivals. The interpretation of these echelon arrivals as multiples supersedes an earlier interpretation which attributed them to successive primary reflections arising from alternating high- and low-velocity layers. Synthetic seismogram modeling indicates that a low-velocity zone with transitional upper and lower boundaries generates peg-leg multiples as effectively as one with sharp boundaries. No PmP or Pn arrivals from the subducting oceanic Moho at 30 km depth beneath the western part of the line are observed on the long-offset (90-225 km) data. This may be due to a lower crustal waveguide whose top is the high-velocity (7.6 km/s) layer and whose base is the Moho. A deep (~54 km) reflector is not affected by the waveguide and has been identified in the data. Although peg-leg multiples have been interpreted on some long-range refraction profiles that sound to upper mantle depths, the Chugach Mountains profile is one of the few crustal refraction profiles where peg-leg multiples are clearly observed. This study indicates that multiple and converted phases may be more important in seismic refraction/wide-angle reflection profiles than previously recognized.
    Type: Article , PeerReviewed
    Format: text
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  • 7
    Publication Date: 2018-07-16
    Description: The convergent margin of the central Sunda Arc in Indonesia was the target of a reflection and refraction seismic survey conducted in 1998 and 1999. Along two seismic lines across the subduction complex off southern Sumatra and off Sunda Strait, coincident multichannel and wide-angle data were collected, complemented by two refraction strike-lines in the forearc basin off Sumatra. The combined analysis of the acquired data allows us to present a detailed model of the subduction zone where initiation of strain partitioning occurs due to the onset of oblique subduction. The dip of the subducted plate is well defined along both dip-lines and a lateral increase from 5° to 7° from beneath the outer high off Sumatra to Sunda Strait is supported by complementary gravity modelling. The downgoing slab is traced to a depth of more than 30km. On both reflection dip-lines, a clearly developed backstop structure underlying a trench slope break defines the landward termination of the active accretionary prism and separates it from the outer high. Active subduction accretion is supported by laterally increasing velocities between the deformation front and the active backstop structure. Seismic velocities of the outer high are moderate along both lines (〈5.8kms−1 at 20km depth), suggesting a sedimentary composition. Reduced reflectivity beneath a rugged top basement traced along the outer high of both dip-lines supports a high degree of deformation and material compaction. Several kilometres of sediment has accumulated in the forearc domain, although a distinct morphological basin is only recognized off southern Sumatra and is not developed off Sunda Strait. The bathymetric elevation of the Java shelf that is encountered in the southern Sunda Strait corresponds to increased velocities of a basement high there and is connected to extensional structures of the Sunda Strait transtensional basin. Differences observed in the morphology of the forearc domain are also reflected in the lower crustal structure. Off southern Sumatra, the velocity–depth model clearly indicates a continental-type crust underlying the forearc basin, whereas lower velocities are found beneath the Sunda Strait forearc domain. Off Sumatra, some 3-D constraint on the upper plate structure is gained from the refraction strike-lines, which in addition is supported by synthetic data modelling.
    Type: Article , PeerReviewed
    Format: text
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  • 8
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research - Solid Earth, 94 (B1). pp. 625-636.
    Publication Date: 2018-03-06
    Description: During a seismic reflection survey conducted by the California Consortium for Crustal Studies in the Basin and Range Province west of the Whipple Mountains, SE California, a piggyback experiment was carried out to collect intermediate offset data (12–31 km). These data were obtained by recording the Vibroseis energy with a second, passive recording array, deployed twice at fixed positions at opposite ends of the reflection lines. The reflection midpoints fall into a 3-km-wide and 15-km-long region in Vidal Valley, roughly parallel to a segment of one of the near-vertical reflection profiles. This data set makes three unique contributions to the geophysical study of this region. (1) From forward modeling of the observed travel times using ray-tracing techniques, a shallow layer with velocities ranging from 6.0 to 6.5 km/s was found. This layer dips to the south from 2-km depth near the Whipple Mountains to a depth of 5-km in Rice Valley. These depths correspond closely to the westward projection of the Whipple detachment fault, which is exposed 1 km east of the near-vertical profiles in the Whipple Mountains. (2) On the near-vertical profile, the reflections from the mylonitically deformed lower plate at upper crustal and mid crustal depths are seen to cease underneath a sedimentary basin in Vidal Valley. However, the piggyback data, which undershoot this basin, show that these reflections are continuous beneath the basin. Thus near-surface energy transmission problems were responsible for the apparent lateral termination of the reflections on the near-vertical reflection profile. (3) The areal distribution of the midpoints allows us to construct a quasi-three-dimensional image on perpendicular profiles; at the cross points we determined the true strike and dip of reflecting horizons. This analysis shows that the reflections from the mylonitically deformed lower plate dip to the southwest westward of the Whipple Mountains and dip to the south southward of the Turtle Mountains. The results of this study support the interpretation of crustal reflectivity in the near-vertical reflection profiles to be related to the mid-Tertiary episode of extension which produced the Whipple metamorphic core complex. This association geometrically suggests a more regionally distributed mechanism for crustal thinning as compared with single detachment fault models.
    Type: Article , PeerReviewed
    Format: text
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  • 9
    Publication Date: 2019-01-21
    Description: At convergent margins, the structure of the subducting oceanic plate is one of the key factors controlling the morphology of the upper plate. We use high-resolution seafloor mapping and multichannel seismic reflection data along the accretionary Sumatra trench system to investigate the morphotectonic response of the upper plate to the subduction of lower plate fabric. Upper plate segmentation is reflected in varying modes of mass transfer. The deformation front in the southern Enggano segment is characterized by neotectonic formation of a broad and shallow fold-and-thrust belt consistent with the resumption of frontal sediment accretion in the wake of oceanic relief subduction. Conversely, surface erosion increasingly shapes the morphology of the lower slope and accretionary prism towards the north where significant oceanic relief is subducted. Subduction of the Investigator Fracture Zone and the fossil Wharton spreading centre in the Siberut segment exemplifies this. Such features also correlate with an irregularly trending deformation front suggesting active frontal erosion of the upper plate. Lower plate fabric extensively modulates upper plate morphology and the large-scale morphotectonic segmentation of the Sumatra trench system is linked to the subduction of reactivated fracture zones and aseismic ridges of the Wharton Basin. In general, increasing intensity of mass-wasting processes, from south to north, correlates with the extent of oversteepening of the lower slope (lower slope angle of 3.8 degrees in the south compared with 7.6 degrees in the north), probably in response to alternating phases of frontal accretion and sediment underthrusting. Accretionary mechanics thus pose a second-order factor in shaping upper plate morphology near the trench.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2018-01-19
    Description: Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp 〉 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is 〉10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp 〉 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for.
    Type: Article , PeerReviewed
    Format: text
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