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  • 1
    Electronic Resource
    Electronic Resource
    ^1^4N quadrupole coupling in DAN and MBANP
    Amsterdam : Elsevier
    Chemical Physics Letters 167 (1990), S. 588-590 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(90)85474-Q
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  • 2
    Electronic Resource
    Electronic Resource
    Mapping the Hawaiian plume conduit with converted seismic waves (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 405 (2000), S. 938-941 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The volcanic edifice of the Hawaiian islands and seamounts, as well as the surrounding area of shallow sea floor known as the Hawaiian swell, are believed to result from the passage of the oceanic lithosphere over a mantle hotspot. Although geochemical and gravity observations indicate ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35016054
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  • 3
    Electronic Resource
    Electronic Resource
    Subduction and collision processes in the Central Andes constrained by converted seismic phases (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 958-961 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Central Andes are the Earth's highest mountain belt formed by ocean–continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35050073
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  • 4
    Electronic Resource
    Electronic Resource
    Inversion of teleseismic S particle motion for azimuthal anisotropy in the upper mantle: a feasibility study (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: We have developed a technique for the inversion of teleseismic S-waveforms in terms of azimuthal anisotropy in the upper mantle. We test different models of the Earth upper mantle by transforming the observed horizontal components into a synthetic vertical component and comparing this with the observed vertical component. The optimum model is found by minimizing the difference between the synthetic vertical component and the observed one. Using this method, we explore the possibility of constraining the distribution of azimuthal anisotropy with depth.We present examples of seismic observations where the data are clearly in favour of an anisotropic model. These observations can be interpreted in terms of two anisotropic layers with different directions of fast velocity axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb03905.x
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 101 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In order to better understand the causes of unprecedented damage to Mexico City during the 1985 September 19 Michoacan earthquake (Mw= 8.0) spectral ratios of teleseismic P-waves of this earthquake are studied with respect to those from five recent, large Mexican subduction zone earthquakes (7.0 ≤Mw≤ 7.7). The data are from vertical-component digital seismographs. It is found that the spectral ratios at stations in the NE quadrant are anomalously more energetic than those predicted by the ω−2 source model in the critical frequency range for Mexico City (0.3-0.7 Hz). The evidence is especially convincing for the spectral ratios with respect to the earthquakes of 1985 September 21 (Mw= 7.6) and 1986 (Mw= 7.0) since the data are available from several stations in the NE quadrant. The teleseismic P-wave spectral ratio in this quadrant with respect to the 1985 September 21 earthquake, in the critical frequency range, is close to the acceleration spectral ratio found in and near Mexico City (also in the NE quadrant). Velocity traces in the epicentral region of the Michoacan earthquake, obtained by integrating the accelerograms, also show oscillations with a frequency of about 0.4 Hz. Furthermore, a regression study of Fourier acceleration spectra at a hill-zone site in Mexico City demonstrates that the Michoacan earthquake was anomalously energetic in the city at the critical frequencies for an event of that magnitude and at that distance. If the data from 7.0 ≤Mw≤ 7.7 events can be extrapolated to estimate the ground motions from Mw≥ 8.0 earthquakes, then the evidence, supports an anomalously large body-wave radiation towards Mexico City between 0.3 and 0.7 Hz during the Michoacan earthquake. This anomalous radiation and the dramatic local amplification of seismic waves in the lake-bed zone of the city (∼ 10–50 times at frequencies between 0.3 and 0.7 Hz) appear to be the principal natural causes of the disaster. The anomalous teleseismic P-wave spectral ratios with respect to the earthquakes of 1985 September 21 and 1986 found in the NE quadrant are not observed in the data available from a small number of stations in the other quadrants. If this observation is true then it suggests a directional property to the anomalous radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb00756.x
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  • 6
    Electronic Resource
    Electronic Resource
    Broadband observations of PS conversions from the upper mantle in Eurasia (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The delay-and-sum method by Vinnik (1977) to detect weak PS conversions in the P coda is applied to German, Czechoslovakian and Chinese broadband data. Clear phases (a factor 4-5 above the noise level) are observed in the 3-11 s period band from the 670 and 400 km discontinuities after summing several hundred traces. The decisive step to obtain such a good signal-to-noise ratio was the summation of records from stations in different regions. The summation of a large number (many hundreds) of traces of a single station does not result in similar improvements because of coherent signal-generated noise due to scattering below the station. There are weak indications of a 520 km discontinuity in our data. The delay times relative to P of the converted phases are stable within 1 s between central Europe and China.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb00814.x
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  • 7
    Electronic Resource
    Electronic Resource
    Receiver functions at the stations of the German Regional Seismic Network (GRSN) (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Several years of broad-band teleseismic data from the GRSN stations have been analysed for crustal structure using P-to-S converted waves at the crustal discontinuities. An inversion technique was developed which applies the Thomson-Haskell formalism for plane waves without slowness integration. The main phases observed are Moho conversions, their multiples in the crust, and conversions at the base of the sediments. The crustal thickness derived from these data is in good agreement with results from other studies. For the Gräfenberg stations, we have made a more detailed comparison of our model with a previously published model obtained from refraction seismic experiments. The refraction seismic model contains boundaries with strong velocity contrasts and a significant low-velocity zone, resulting in teleseismic waveforms that are too complicated as compared to the observed simple waveforms. The comparison suggests that a significant low-velocity zone is not required and that internal crustal boundaries are rather smooth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb03520.x
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  • 8
    Electronic Resource
    Electronic Resource
    A global study of S-to-P and P-to-S conversions from the upper mantle transition zone (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 107 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: bLong-period data of the Global Digital Seismograph Network (GDSN) recorded over the three-year period from 1984 to 1986 were studied for the occurrence of S-P and P-S conversions from the upper mantle transition zone that appear as precursors to teleseismic S arrivals. Conversions of this type were identified on a large number of single-station records. Simple stacking of many records enhanced the appearance of converted phases and demonstrated that no major lateral variations in the nature of the transition zone exist between various tectonic regions. S-P and P-S conversions from the 400 km discontinuity were best observed at distances between 70d̀ and 85d̀ while conversions from the 670 km discontinuity showed up best at distances beyond 87d̀. The analysis of published source mechanisms and comparison with synthetic seismograms suggests that the appearance of converted phases is primarily governed by the earthquake radiation pattern. Phases that have undergone S-P conversions beneath the receiver are best observed from dip-slip events that radiate strong SV- and weak P-waves towards the station. P-S conversions beneath the source area, on the other hand, are frequently observed from events that radiate strong P and little SV energy towards the station, and also from some strike-slip events. Comparison of observed with synthetic seismograms suggests that the PREM model of Dziewonski & Anderson (1981) explains most of the observations. Observed S-P and P-S conversions from the 670 km discontinuity, however, often have larger amplitudes than in the synthetics. Constructive interference of converted waves with the P-wave coda, source radiation effects and a velocity contrast across the 670 km discontinuity which is higher than in PREM may all contribute to the discrepancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb01161.x
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  • 9
    Electronic Resource
    Electronic Resource
    Ellipticity of Teleseismic S-Particle Motion (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: In the horizontal components of GRF records, particle motions of the teleseismic S waves in the period range between 5 and 20s are usually elliptic. We correct the particle motions for the effect of azimuthal anisotropy at GRF and explain the residual ellipticity by assuming that it is produced at the source side of the wave path by interference of two waves with orthogonal polarizations and differing traveltimes. the estimates of polarization direction of the fast wave and time delay between the waves can be found by analysing the residual particle motion for groups of closely spaced seismic events. the technique was applied to about 40 GRF records of events from the northern and north-western Pacific. In the source regions the S-wave pulses propagate in subduction zones. It is found that the surface projections of polarization of the fast wave of the shallow events coincide approximately with the strikes of the corresponding island arcs. This regularity can be explained by anisotropy in the subduction zones provided that the a axis of olivine is parallel to the plane of subduction. the fast direction for the deep events in the sea of Japan and the sea of Okhotsk is close to the strike of the Kurile island arc. the time delay between the fast and the slow waves for the deep events is smaller than for the shallow Kurile events (0.9s versus 1.4s).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb02537.x
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  • 10
    Electronic Resource
    Electronic Resource
    Inversion of source parameters for subcrustal earthquakes in the Hellenic Arc (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 103 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A one-station method was developed to invert simultaneously for seismic moment, focal depth, and the orientations of the nodal planes. This method was tested on seismograms recorded at the broadband Gréfenberg array (GRF) for earthquakes in the central to eastern Hellenic arc and southern Turkey. The complete P and S body-wave responses, including all near source surface reflections, were synthesized using the reflectivity method. The minimum misfit between the observed and theoretical seismograms in the WWSSN-LP band was determined by cross-correlation, searching the whole parameter space of strike, dip and rake of a pair of orthogonal nodal planes, and adjusting the source depth and seismic moment. The initial searching step of 20° was reduced to 5° in the vicinity of the minimum misfit position, for a final search. The best fitting solution was then compared to the Harvard (HRVD) moment tensor solution best double couple which was derived using long-period data and to the P-wave first motion polarities reported by the ISC. Most solutions based on GRF data agree well with those found by HRVD, but in some cases some features of the observed GRF signals cannot be matched by the HRVD solution or solutions similar to it.The nine earthquakes we analysed in detail had magnitudes between 5.2 and 5.8. Our depth determinations ranged from 35 to 155 km. The deepest events (80–155 km) were located near Rhodes and to the east of it. One earthquake located in southern Turkey was confirmed to have a focus at about 125 km depth. The focal mechanisms of the intermediate depth earthquakes in the eastern Hellenic arc show P-axes approximately parallel to the strike of the deep slab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb01783.x
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