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  • 1
    Online-Ressource
    Online-Ressource
    American Geophysical Union (AGU) ; 1988
    In:  Journal of Geophysical Research: Solid Earth Vol. 93, No. B2 ( 1988-02-10), p. 1119-1130
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 93, No. B2 ( 1988-02-10), p. 1119-1130
    Kurzfassung: Coincident multichannel seismic reflection and refraction data from a N–S transect near Oahu, Hawaii, provide evidence for thickening of the Pacific crust by 1–2 ± 1 km south of the large‐offset (16 m.y.) Molokai Fracture Zone (FZ). Tau‐p stacks, tau‐sum inversions, and forward modeling of the refraction data indicate that the crustal thickening occurs primarily within the lower portion of seismic layer 2. Assuming isostatic balance, the differences in crustal thickness predict that seafloor having the same age will have different elevations across the FZ. Observations of sea‐floor depths across the FZ east of the Hawaiian Islands are consistent with this prediction implying that the processes which have generated the crustal differences have been stable for over 50 m.y. Previous correlations between the chemical composition of ridge crest basalts, crustal thickness, and ridge crest elevation have been attributed to variations in the thermal regime of the upper mantle under mid‐ocean spreading centers. In accord with this hypothesis, we propose that the observed differences in crustal structure across the Molokai FZ may have been produced by small (25°C) differences in the thermal regime of the upper mantle beneath the ancestral East Pacific Rise. Discontinuous intracrustal reflections located about 1.6 s below the sediment/basement interface are observed in migrated reflection data south of Oahu. These reflections are similar in character to the lower crustal “Horizon R” event observed in the western North Atlantic. Shallower intracrustal reflections, possibly from within seismic layer 2, are also observed. The observation of these intracrustal reflections in both the Atlantic and Pacific oceans suggests that they are a fundamental signature of the crustal accretion process at a variety of spreading rates and that they are mappable using modern seismic reflection/refraction methods.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1988
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Online-Ressource
    Online-Ressource
    American Geophysical Union (AGU) ; 1987
    In:  Journal of Geophysical Research: Solid Earth Vol. 92, No. B3 ( 1987-03-10), p. 2647-2661
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 92, No. B3 ( 1987-03-10), p. 2647-2661
    Kurzfassung: Analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant, systematic, and symmetric dependence of average layer 2 velocities on their distance to the north and south of the Hawaiian ridge. Beyond the flexural arch surrounding the ridge the velocity‐depth solutions indicate a normal layer 2. Within the arch (approximately 155 km from the ridge) the average elastic velocities in layer 2 are lowered by 0.8–0.9 ± 0.2 km/s. Within 75 km of the ridge the average velocities are again normal. Elastic and elastic‐plastic flexural models for the regional compensation of the Hawaiian islands predict tensional stress drops of 0.8 kbar in the upper lithosphere for the region having lowered velocities in layer 2, which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0.5 km/s. A significant inverse relationship (correlation coefficient of 0.818) exists between the average elastic velocities in the upper 1.0 km of the igneous crust and the strain in the upper crust calculated from these flexural models. The correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure. These observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1987
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 77, No. 18 ( 1996-04-30), p. 173-176
    Kurzfassung: The Whittier Narrows earthquake of 1987 and the Northridge earthquake of 1991 highlighted the earthquake hazards associated with buried faults in the Los Angeles region. A more thorough knowledge of the subsurface structure of southern California is needed to reveal these and other buried faults and to aid us in understanding how the earthquake‐producing machinery works in this region.
    Materialart: Online-Ressource
    ISSN: 0096-3941 , 2324-9250
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1996
    ZDB Id: 24845-9
    ZDB Id: 2118760-5
    ZDB Id: 240154-X
    SSG: 16,13
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  • 4
    Online-Ressource
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    American Geophysical Union (AGU) ; 1987
    In:  Journal of Geophysical Research: Solid Earth Vol. 92, No. B13 ( 1987-12-10), p. 13687-13707
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 92, No. B13 ( 1987-12-10), p. 13687-13707
    Kurzfassung: Coincident multichannel seismic reflection and refraction data acquired during a wide‐aperture two‐ship experiment provide evidence for a complex crust‐mantle (C‐M) transition under Oahu, Hawaii. Several large‐aperture common depth point lines and three expanding spread profiles suggest the existence of an anomalously thick (3–6 km) C‐M transition zone underneath the volcanic ridge which extends for distances of 100 km to the north and south from the center of Oahu. The anomalous C‐M transition may represent a plutonic complex which intruded into the upper mantle and the lower crust in a 200‐km‐wide area centered at Oahu. The existence of such a large volume of intrusions near the base of the crust implies that the surficial expression of volcanism constitutes only a small fraction of the amount of melt generated at depth under the Hawaiian Islands. This interpretation is in accord with previous petrological models which predict trapping and accumulation of upwelling magma at and below the Moho. We have constructed a model which suggests that the interaction between the upwelling magma and the lithospheric flexural stress field may modulate the characteristic eruption history of Hawaiian volcanoes. In particular, the model for the plane stress field which accompanies the flexure of the oceanic crust around island chains indicates that the stress field under individual volcanoes varies considerably with its position relative to the tip of the chain. As a Hawaiian‐sized volcano develops, the magnitude of deviatoric compressive stresses under it is probably sufficient to block the conduits of the upwelling magma within the oceanic crust and to terminate eruptions. Further upwelling magma is predicted by the models to be ponded at the base of the crust. Resumption of posterosional volcanism seems to occur at a constant distance behind the center of active shield volcanism, as the horizontal compressive stresses along the axis of the chain are released. Observed orientations of dikes of this volcanic phase agree with the directions of the maximum calculated stresses. Our model implies that magma upwells over a 300‐km‐wide zone and that the oceanic plate may not be fractured under the islands.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1987
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Online-Ressource
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    American Geophysical Union (AGU) ; 2000
    In:  Eos, Transactions American Geophysical Union Vol. 81, No. 46 ( 2000-11-14), p. 545-552
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 81, No. 46 ( 2000-11-14), p. 545-552
    Kurzfassung: In the past decade, Earth scientists have recognized the seismic hazards that crustal faults and sedimentary basins pose to Seattle, Washington (Figure 1). In 1998, the US. Geological Survey and its collaborators initiated a series of urban seismic studies of the upper crust to better map seismogenic structures and sedimentary basins in the Puget Lowland. These studies are called the Seismic Hazard Investigations of Puget Sound (SHIPS). In March 1998, we conducted our first SHIPS study, an investigation of the upper crustal structure of the Puget Lowland, using marine airgun sources and land recorders [ Fisher et al. , 1999].The study was nicknamed Wet SHIPS. In September 1999, we obtained a seismic refraction line to study the upper crustal structure in the Seattle area in a land‐based study nicknamed Dry SHIPS [ Brocher et al. , 2000] (Figure 1). In March 2000, we recorded the demolition of the Seattle Kingdome sports stadium using a dense array of seismic recorders for a detailed site response study; this study was nicknamed Kingdome SHIPS (Figure 1).
    Materialart: Online-Ressource
    ISSN: 0096-3941 , 2324-9250
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2000
    ZDB Id: 24845-9
    ZDB Id: 2118760-5
    ZDB Id: 240154-X
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Online-Ressource
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    American Geophysical Union (AGU) ; 1996
    In:  Journal of Geophysical Research: Solid Earth Vol. 101, No. B10 ( 1996-10-10), p. 22311-22334
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 101, No. B10 ( 1996-10-10), p. 22311-22334
    Kurzfassung: Wide‐angle seismic data collected during the Bay Area Seismic Imaging Experiment provide new glimpses of the deep structure of the San Francisco Bay Area Block and across the offshore continental margin. San Francisco Bay is underlain by a veneer ( 〈 300 m) of sediments, beneath which P wave velocities increase rapidly from 5.2 km/s to 6.0 km/s at 7 km depth, consistent with rocks of the Franciscan subduction assemblage. The base of the Franciscan at 15–18 km depth is marked by a strong wide‐angle reflector, beneath which lies an 8‐ to 10‐km‐thick lower crust with an average velocity of 6.75 ± 0.15 km/s. The lower crust of the Bay Area Block may be oceanic in origin, but its structure and reflectivity indicate that it has been modified by shearing and/or magmatic intrusion. Wide‐angle reflections define two layers within the lower crust, with velocities of 6.4–6.6 km/s and 6.9–7.3 km/s. Prominent subhorizontal reflectivity observed at near‐vertical incidence resides principally in the lowermost layer, the top of which corresponds to the “6‐s reflector” of Brocher et al. [1994]. Rheological modeling suggests that the lower crust beneath the 6‐s reflector is the weakest part of the lithosphere; the horizontal shear zone suggested by Furlong et al. [1989] to link the San Andreas and Hayward/Calaveras fault systems may actually be a broad zone of shear deformation occupying the lowermost crust. A transect across the continental margin from the paleotrench to the Hayward fault shows a deep crustal structure that is more complex than previously realized. Strong lateral variability in seismic velocity and wide‐angle reflectivity suggests that crustal composition changes across major transcurrent fault systems. Pacific oceanic crust extends 40–50 km landward of the paleotrench but, contrary to prior models, probably does not continue beneath the Salinian Block, a Cretaceous arc complex that lies west of the San Andreas fault in the Bay Area. The thickness (10 km) and high lower‐crustal velocity of Pacific oceanic crust suggest that it was underplated by magmatism associated with the nearby Pioneer seamount. The Salinian Block consists of a 15‐km‐thick layer of velocity 6.0–6.2 km/s overlying a 5‐km‐thick, high‐velocity (7.0 km/s) lower crust that may be oceanic crust, Cretaceous arc‐derived lower crust, or a magmatically underplated layer. The strong structural variability across the margin attests to the activity of strike‐slip faulting prior to and during development of the transcurrent Pacific/North American plate boundary around 29 Ma.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1996
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Online-Ressource
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    Informa UK Limited ; 1999
    In:  International Geology Review Vol. 41, No. 3 ( 1999-03), p. 263-274
    In: International Geology Review, Informa UK Limited, Vol. 41, No. 3 ( 1999-03), p. 263-274
    Materialart: Online-Ressource
    ISSN: 0020-6814 , 1938-2839
    Sprache: Englisch
    Verlag: Informa UK Limited
    Publikationsdatum: 1999
    ZDB Id: 2070023-4
    ZDB Id: 2122950-8
    SSG: 13
    SSG: 7,41
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Online-Ressource
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    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Solid Earth Vol. 105, No. B3 ( 2000-03-10), p. 5835-5857
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 105, No. B3 ( 2000-03-10), p. 5835-5857
    Kurzfassung: We use new seismic and gravity data collected during the 1994 Los Angeles Region Seismic Experiment (LARSE) to discuss the origin of the California Inner Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core complex mode. The data provide detailed crustal structure of the Borderland and its transition to mainland southern California. Using tomographic inversion as well as traditional forward ray tracing to model the wide‐angle seismic data, we find little or no sediments, low (≤6.6 km/s) P wave velocity extending down to the crust‐mantle boundary, and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal California, we do not find evidence for an underplated fossil oceanic layer at the base of the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the shelf edge, which represents the transition to the western Transverse Ranges. On the shelf the Palos Verdes Fault merges downward into a landward dipping surface which separates “basement” from low‐velocity sediments, but interpretation of this surface as a detachment fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina Schist rocks extending from top to bottom of the crust. This interpretation is compatible with a model for the origin of the ICB as an autochthonous formerly hot highly extended region that was filled with the exhumed metamorphic rocks. The basin and ridge topography and the protracted volcanism probably represent continued extension as a wide rift until ∼13 m.y. ago. Subduction of the young and hot Monterey and Arguello microplates under the Continental Borderland, followed by rotation and translation of the western Transverse Ranges, may have provided the necessary thermomechanical conditions for this extension and crustal inflow.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2000
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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