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  • 1
    Microfilm
    Microfilm
    Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica (2004)
    Associated volumes
    Details Availability
    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
    DOI: 10.1029/2003JB002931
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    Shear partitioning near the central Japan triple junction: the 1923 great Kanto earthquake revisited—II (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The faulting mechanism of the 1923 great Kanto earthquake is re-examined. The new fault model is constrained by: (1) the focal mechanism of the main shock; (2) triangulation data; (3) levelling data; (4) the distribution of aftershocks; (5) the geology of the ocean floor east of the Boso peninsula; and (6) the delineation of lateral variations in the dip of the subducting Philippine Sea plate. While factors (1)–(4) have been used to constrain earlier fault models, factor (5) leads us to propose the rupture of a major right-lateral fault (here named the Boso transform fault) which accommodated about 1.6 m of slip in the 1923 earthquake. Kinematic constraints derived from the 1923 main-shock fault geometry suggest that the Boso transform fault accommodates about 1.6 cm yr−1 of the relative plate motion, in agreement with onland and marine geology and the uplift history of the Boso peninsula. All plausible fault models of the 1923 earthquake involve right-lateral slip of the Boso transform fault. Triangulation data are better explained by a model which specifies shallower dip of the subducting Philippine Sea slab southeast of the Miura peninsula, consistent with seismological observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04710.x
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  • 3
    Electronic Resource
    Electronic Resource
    Global tomography from Rayleigh and Love wave dispersion: effect of ray-path bending (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 118 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A large data set of fundamental-mode Rayleigh and Love wave phases has been employed for global tomographic inversions. These data represent observations of the first arriving surface waves R1 and L1 from approximately 850 seismic events, with about 10 observations of dispersion per event. The inversion for laterally varying depth-dependent structure is performed in several steps. At discrete periods from 111s–250s for Love waves, and from 111s–200s for Rayleigh waves, we first determine simultaneously the global distribution of phase-velocity anomaly and the relocations of the seismic events. Each phase-velocity distribution is then corrected for laterally varying Moho depth and bathymetry, followed by inversion for 3-D earth structure in the depth range 0–240 km. In order to lie within the limits of ray theory we restrict all model perturbations to a degree 0–16 spherical-harmonic expansion. A second-order scattering (ray path) correction is included in the inversions. The phase-velocity perturbations show a high correlation with surface tectonics at shorter periods. Comparison of inversions shows that those performed without the ray-path correction exhibit a complicated pattern of fast- and slow-velocity bias. The only common feature in the patterns of bias (with respect to period or wave type) is that fast velocity bias is concentrated in regions of large structural gradient. The amplitude pattern of the depth-dependent model has pronounced peaks in the intervals 0–70 km and 140–210 km. The deeper peak is associated with lateral variations in asthenosphere structure. We derive new estimates for the spherically averaged phase velocities of the fundamental-mode Rayleigh and Love waves. The spherically averaged phase velocities are decreased by about 0.1 per cent by including the ray-path correction. These phase-velocity dispersions can be simultaneously fit well with an isotropic model either with or without the ray-path correction, but particularly well when the ray-path correction is included. In both cases a pronounced low-velocity zone of the global extent is required in the depth range 120–190 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb03997.x
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of Rayleigh wave refraction from three-component seismic spectra (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 113 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Lateral refraction of intermediate period surface waves is caused by horizontal gradients in local phase velocity in the vicinity of the source-receiver minor arc. For smooth structural perturbations, this is manifested by an off-azimuth arrival (azimuth deviation) of the Airy phase. We present a method for estimating azimuth deviation as a function of frequency for Rayleigh waves observed on a three-component seismogram. By taking advantage of the different dispersion characteristics of the Rayleigh and Love wave group arrivals, the method essentially constructs an optimal narrow-band taper for each frequency component, in order to minimize the effect of Love wave contamination in the Rayleigh wave azimuth estimation. We have measured the frequency-dependent azimuth deviation of fundamental mode Rayleigh waves of period 20-100s under a variety of conditions. The most coherent results are obtained for (1) seismic records with a relatively high Rayleigh wave excitation, (2) ray paths which are confined to purely oceanic or purely continental lithosphere, and (3) ray paths of intermediate offset (30°-50°).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb04657.x
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  • 5
    Electronic Resource
    Electronic Resource
    Propagation of surface waves on a laterally heterogeneous earth: asymptotic solution of the two-dimensional wave equation (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 111 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The two-dimensional wave equation is used to represent the propagation of surface waves on a laterally heterogeneous earth. Assuming sufficiently smooth variations in earth structure, expressions for the wavefield potentials and their associated displacement spectra are derived up to second-order scattering interactions. Up to first-order scattering, these expressions are shown to be equivalent to the results obtained from the coupling of normal modes along a common dispersion branch. The second-order scattering wavefield appears as a negatively phase-shifted perturbation which acts to decrease the apparent phase velocity of the arriving wavelet. Synthetic experiments demonstrate that significant bias in earth structure inversions may be introduced by neglecting such effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00555.x
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  • 6
    Electronic Resource
    Electronic Resource
    Multiple moment expansion of fully coupled aspherical earth seismograms (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 106 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An asymptotic theory is developed to generate long-period synthetic seismograms on the aspherical earth. For given source and receiver, the method requires only the knowledge of aspherical earth structure along the source-receiver great circle, as well as the transverse gradients and curvature of this structure along the great circle. The theory is developed here for spheroidal modes observed on the vertical component. Each isolated spheroidal mode pSl is represented in the time domain by a truncated Taylor series expansion, with the nth expansion coefficient expressed as the nth moment of the multiplet spectrum about a fiducial frequency. The resulting expansions are valid up to order 1/l and account for all of the effects associated with refraction and focusing of the equivalent surface waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb04617.x
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  • 7
    Electronic Resource
    Electronic Resource
    Coseismic Deformation From Earthquake Faulting On A Layered Spherical Earth (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A method for calculating the static displacement field following earthquake faulting in a layered spherical earth is presented. At shallow levels, the Earth's layering is characterized by sharp jumps in bulk and shear moduli at the Conrad discontinuity and the Moho and is therefore important to consider when evaluating crustal deformation. the solution to the equations of static equilibrium is represented as a superposition of spheroidal and toroidal components that each depend on spherical harmonic degree and the moment tensor. A method that has recently been applied to the problem of wave propagation on a layered spherical earth is here applied to the static deformation field. By representing the point source in terms of discontinuities in the displacement-stress vector, the Green's function for a particular source geometry is derived directly. Numerical tests are presented to verify the accuracy of the method and to illustrate the effects of sphericity and layering on the calculated deformation fields. the effect of sphericity is generally less than about 2 per cent (of maximum deformation) within 100 km of an earthquake source at crustal depths. Comparisons between the deformation calculated on a spherical homogeneous earth and spherical layered earth show that up to 20 per cent errors would be introduced if the Earth's layered structure were ignored. the effect of layering is strongest for sources with a strong horizontal slip component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06530.x
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  • 8
    Electronic Resource
    Electronic Resource
    Pliocene change in Pacific-plate motion (1986)
    [s.l.] : Nature Publishing Group
    Nature 320 (1986), S. 738-741 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The 15--3 Myr segments of every young Pacific chain, with the exception of the Marquesas, are fit very well by Epp's 15-1 Myr stage pole (65‚ N 40‚ W; 0.84‚ Myr"1). There is, however, a large discrepancy between the observed and predicted trends of the Caroline Islands (Fig. I/) after 5.2 Myr (the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/320738a0
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  • 9
    Electronic Resource
    Electronic Resource
    From rifting to drifting (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 398 (1999), S. 21-22 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Africa is splitting apart down the East African Rift. An analysis of the relative motion of the tectonic plates involved allows the rate of continental rifting to be estimated. Geologists are naturally drawn to modern examples of fundamental processes that have occurred over long stretches ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/17913
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  • 10
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    Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica (2004)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 109 . B11403.
    Details
    Publication Date: 2018-04-25
    Description: 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 block–Caribbean boundary. The GPS data suggest that the Cocos plate–Panama 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: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2003JB002931
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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