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  • 1
    In: Journal of geophysical research / B, Washington, DC : Union, 1978, 0148-0227
    Description / Table of Contents: New seismic and geodetic data from Costa Rica provide insight into seismogenic zone processes in Central America, where the Cocos and Caribbean plates converge. Seismic data are from combined land and ocean bottom deployments in the Nicoya peninsula in northern Costa Rica and near the Osa peninsula in southern Costa Rica. In Nicoya, inversion of GPS data suggests two locked patches centered at 14 ± 2 and 39 ± 6 km depth. Interplate microseismicity is concentrated in the more freely slipping intermediate zone, suggesting that small interseismic earthquakes may not accurately outline the updip limit of the seismogenic zone, the rupture zone for future large earthquakes, at least over the short (~1 year) observation period. We also estimate northwest motion of a coastal "sliver block" at 8 ± 3 mm/yr, probably related to oblique convergence. In the Osa region to the south, convergence is orthogonal to the trench. Cocos-Caribbean relative motion is partitioned here, with ~8 cm/yr on the Cocos-Panama block boundary (including a component of permanent shortening across the Fila Costeña fold and thrust belt) and ~1 cm/yr on the Panama blockCaribbean boundary. The GPS data suggest that the Cocos platePanama block boundary is completely locked from ~10-50 km depth. This large locked zone, as well as associated forearc and back-arc deformation, may be related to subduction of the shallow Cocos Ridge and/or younger lithosphere compared to Nicoya, with consequent higher coupling and compressive stress in the direction of plate convergence.
    Type of Medium: Microfilm
    Pages: graph. Darst
    ISSN: 0148-0227
    Language: English
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  • 2
    Publication Date: 2022-05-26
    Description: Author Posting. © The Oceanography Society, 2014. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 27, no. 2 (2014): 138-150, doi:10.5670/oceanog.2014.49.
    Description: Increasing public awareness that the Cascadia subduction zone in the Pacific Northwest is capable of great earthquakes (magnitude 9 and greater) motivates the Cascadia Initiative, an ambitious onshore/offshore seismic and geodetic experiment that takes advantage of an amphibious array to study questions ranging from megathrust earthquakes, to volcanic arc structure, to the formation, deformation and hydration of the Juan De Fuca and Gorda Plates. Here, we provide an overview of the Cascadia Initiative, including its primary science objectives, its experimental design and implementation, and a preview of how the resulting data are being used by a diverse and growing scientific community. The Cascadia Initiative also exemplifies how new technology and community-based experiments are opening up frontiers for marine science. The new technology—shielded ocean bottom seismometers—is allowing more routine investigation of the source zone of megathrust earthquakes, which almost exclusively lies offshore and in shallow water. The Cascadia Initiative offers opportunities and accompanying challenges to a rapidly expanding community of those who use ocean bottom seismic data.
    Description: The Cascadia Initiative is supported by the National Science Foundation; the CIET is supported under grants OCE- 1139701, OCE-1238023, OCE‐1342503, OCE-1407821, and OCE-1427663 to the University of Oregon.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 14 (1967), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Earth and Planetary Sciences 32 (2004), S. 403-433 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: The migration of the Mendocino triple junction through central and northern California over the past 25-30 million years has led to a profound change in plate interactions along coastal California. The tectonic consequences of the abrupt change from subduction plate interactions north of the triple junction to the development of the San Andreas transform system south of the triple junction can be seen in the geologic record and geophysical observations. The primary driver of this tectonism is a coupling among the subducting Juan de Fuca (Gorda), North American, and Pacific plates that migrates with the triple junction. This coupling leads to ephemeral thickening of the overlying North American crust, associated uplift and subsequent subsidence, and a distinctive sequence of fault development and volcanism.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 112 (1993), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We analyse the PP phase at upper mantle distances (25° to 60°) to quantify its propagation characteristics and potential for determining crust and upper mantle velocity structure. Upper mantle distance PP waveforms are very complex, involving interference between a variety of arrivals traversing different depth ranges in the Earth. Even for laterally homogeneous structures, complete synthetic seismograms such as provided by reflectivity calculations are required to adequately model the full suite of arrivals that contribute to upper mantle PP phases. the complexity of PP waveforms can be exploited to extract crust and upper mantle structural information for relatively homogeneous paths. While PP-P differential traveltimes and PP/P amplitude ratios provide constraints on average upper mantle velocities above the transition zone, early PP coda, comprized of crustal reflections and conversions, and precursors to the PP phase, comprized of multiple Moho underside reflections, can provide information on crustal thickness and velocity gradients in the uppermost mantle. Positive velocity gradients below the crust generate large amplitude Moho underside reflections that are particularly visible for short-period and broad-band seismograms at distances from 25° to 38°. We demonstrate the potential use of the PP phase for determining upper mantle structure by modelling long-period signals traversing relatively ‘pure’ paths across North America. A continuum of P-wave velocity models with varying lid structure is appropriate for the upper mantle beneath North America. the highest velocities are found beneath the northern Canadian shield, with the lid becoming progressively slower beneath the southern shield, continental platform and tectonically active regions, respectively. Most of the heterogeneity in P-velocity structure is concentrated above a depth of 250km, although some data are consistent with models that are relatively slow at greater depths.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 119 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We model 45 P and PP waveforms at epicentral distances of 14° to 40°, primarily sampling western and central China, to determine regionalized P-wave velocity variations for the crust and upper mantle in this region. Observed P and PP waveforms are matched by 1-D forward modelling using the reflectivity technique. Our approach is to first find a homogeneous average velocity model for China which can match the observed broad-band waveforms filtered with a long-period instrument response. This model is then used as a starting model for the matching of the broad-band waveforms to investigate the lateral velocity variations. Our preferred average model WCH has a 50 km thick crust with a velocity of 6.4 km s−1, a Pn velocity of 8.15 km s−1 and a low-velocity zone between 100 km and 175 km depth. It has intermediate characteristics between an active tectonic region and a stable shield, compatible with previous S-wave modelling results. Modelling of the broad-band waveforms indicates significant lateral deviations from model WCH. For the Tibetan plateau we observe larger crustal thickness (55–70 km) and Pn velocity (8.15–8.25 km s−1) in combination with a low-velocity zone that varies in magnitude throughout the Tibetan region. Lower velocities than our average model may be present below 200 km depth. Our modelling indicates a thin lid of about 30–45 km under Tibet. We infer from our results and previous work that crustal shortening and thickening is the most likely process responsible for the central and northern Tibetan plateau's thick crust and high average elevation, and that the Indian plate has probably only underplated the southernmost part of the plateau. Mantle convection associated with the crustal shortening process has led to strong lateral heterogeneity in the upper mantle under Tibet. Higher Pn velocities in western Tibet might indicate that this region is presently undergoing crustal shortening. Paths traversing eastern China require a constant velocity lid of about 100 km thickness, a Pn velocity of 8.12–8.14 km s−1 and a crustal thickness between 27 and 35 km. A preliminary model for northern China suggests a crustal thickness between 43 and 50 km, a Pn velocity of about 8.0 km s−1 and a 100 km thick lid with a positive velocity gradient for this region.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 794 (1996), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 3 (1967), S. 306-319 
    ISSN: 1432-1106
    Keywords: Neuroglia ; GABA ; Glutamate ; Chemical transmitters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Unresponsive cells in the pericruciate cortex of cats under pentobarbitone were distinguished from neurones by total absence of spontaneous or evoked spikes and synaptic responses. They had much greater membrane potentials (mean −62 mV) and resistances (mean 48 MΩ) than neurones (means −36 mV, 21 MΩ), and the potentials were unusually stable. They could be depolarized by external applications of K+, but were insensitive to internal injections of K+ or Cl−. Unlike neurones, they were not hyperpolarized by GABA or depolarized by L-glutamate, but large doses of GABA had a depolarizing effect, without reducing the membrane resistance. ACh also depolarized some neurones and unresponsive cells without a fall in membrane resistance; but nor-adrenaline and 5HT were ineffective on the few unresponsive cells tested. It is suggested that unresponsive cells are neuroglia; that the depolarizing actions of GABA and ACh indicate a change in electrogenic active transport, and that glia may remove transmitters from the extracellular space.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 3 (1967), S. 320-336 
    ISSN: 1432-1106
    Keywords: Cortex ; Inhibition ; GABA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In cats under pentobarbitone anaesthesia, GABA was tested on cortical, pericruciate neurones and its action compared with IPSPs evoked by surface stimulation. GABA was applied to individual cells by microiontophoresis, while recording the membrane potential and resistance. When K citrate-recording electrodes were used, GABA always hyperpolarized the cell and lowered its resistance, like the synaptic inhibitory effect. By adequate polarization both the action of GABA and the IPSP could be reversed, at a similar level of membrane potential. Both could also be reversed by injecting Cl− into a cell from a KCl recording electrode and the new reversal potentials also did not differ significantly from each other: after this treatment, some cells could be excited with GABA. All these effects of GABA were only seen when it was applied outside the neurones; intracellular injections were ineffective. Since the reversal potentials for the action of GABA and the IPSP are approximately similar, it is concluded that GABA could be the main cortical inhibitory transmitter.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 211 (1966), S. 1372-1374 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Y-AMINOBTJTYRIC acid (GABA) was first identified as a normal constituent of brain tissue in 19501'2. Some years later, GABA was found to have a marked depressant effect on cortical neurones3, and to be a constituent of Factor I an extract of brain tissue found to have a strong inhibitory action on ...
    Type of Medium: Electronic Resource
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