Journal of Physics of the Earth
Online ISSN : 1884-2305
Print ISSN : 0022-3743
ISSN-L : 0022-3743
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Volume 16, Issue 1
Displaying 1-5 of 5 articles from this issue
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  • Effect of Spherical Crustal Layering (SH Waves)
    Ryosuke SATO
    1968 Volume 16 Issue 1 Pages 1-6
    Published: 1968
    Released on J-STAGE: April 30, 2009
    DOIhttps://doi.org/10.4294/jpe1952.16.1
    JOURNAL FREE ACCESS
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    Effect of spherical crustal layering on spectral amplitudes is investigated. Because of quite large value of (radius of boundary)/(wave-length), difference between the transfer functions in plane layering structure and in spherical layering structure is very small, which suggests that assumption of the plane layering is quite satisfactory. However, when considering the layering effect in deeper part of the earth, say, the core boundary layering effect, the curvature may not be ignored especially for rather large angle of incidence.
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  • A Seismic Refraction Exploration of Tosa Deep-Sea Terrace off Sikoku
    Nozomu DEN, Sadanori MURAUCHI, Hiroshi HOTTA, Toshio ASANUMA, Kenji HA ...
    1968 Volume 16 Issue 1 Pages 7-10
    Published: 1968
    Released on J-STAGE: April 30, 2009
    DOIhttps://doi.org/10.4294/jpe1952.16.7
    JOURNAL FREE ACCESS
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    A seismic refraction measurement was made in the Tosa deep-sea terrace south of Sikoku (Shikoku). Thick sediments consisting of 6 layers with velocities of 1.70, 2.04, 2.68, 3.42, 4.07 and 4.58km/sec respectively were found and the total thickness reaches 11km. The 6.89km/sec layer under the sediments could correspond to the oceanic crust in the Sikoku basin.
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  • Q Distribution for Long-Period P Waves in the Mantle
    Takeshi MIKUMO, Tuneto KURITA
    1968 Volume 16 Issue 1 Pages 11-29
    Published: 1968
    Released on J-STAGE: April 30, 2009
    DOIhttps://doi.org/10.4294/jpe1952.16.11
    JOURNAL FREE ACCESS
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    The Q-depth relation in the earth's mantle has been estimated for long-period P waves from two deep-focus and three intermediate earthquakes. The amplitude spectrums of the first P waves from 114 seismograms at recording stations in the distance range between 15 and 103 degrees, have been corrected for the crustal structure and the instrument and used to measure the effects of attenuation over the whole mantle. Probable Q models are presented on the basis of the spectral amplitude ratios between these stations. The low Q between 120 and 280 in the upper mantle shows a rapid increase at depths around 900km to several thousands or greater in the lower mantle, and there is an apparent drop of Q near the base of the mantle. The frequency dependence of the spectral ratios against epicentral distance over about 80 degrees differs for the deep-focus and intermediate earthquakes, suggesting the possible diffraction effects due to the core.
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  • Sequential Occurrences of Recent Great Earthquakes
    Kiyoo MOGI
    1968 Volume 16 Issue 1 Pages 30-36
    Published: 1968
    Released on J-STAGE: April 30, 2009
    DOIhttps://doi.org/10.4294/jpe1952.16.30
    JOURNAL FREE ACCESS
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    Spatial and temporal distributions of epicenters of great shallow earthquakes suggest three migration branches during the last thirty years. In the north-western circum-Pacific seismic belt, which is one of the three migration branches, the epicentral regions of recent great earthquakes were systematically displaced from Japan to Alaska. In this sequential occurrence of great earthquakes, the considered seismic belt was nearly continuously covered by aftershock areas of these earthquakes without any appreciable overlap of aftershock areas. This marked feature provides some important suggestions on the mechanism of earthquake generation.
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  • Some data on seismic waves through the Earth's core
    T.B. YANOVSKAYA
    1968 Volume 16 Issue 1 Pages 37-43
    Published: 1968
    Released on J-STAGE: April 30, 2009
    DOIhttps://doi.org/10.4294/jpe1952.16.37
    JOURNAL FREE ACCESS
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    To construct additional branches of the travel-time curve of PKP waves the residuals of travel times reported in the Bulletins were used. A part of GH branch has been obtained for epicentral distances Δ>145°. The results obtained separately by using the data for shallow and deep earthquakes are in good agreement. The mean slope of this branch was found to be similar to that obtained by ADAMS and RANDALL, but the value of the slope near the end of the branch is in better agreement with that proposed by Bolt. By using the data for deep shocks a part of the trevel-time curve was obtained corresponding to the forerunners for distances Δ<145°. This branch of the travel-time curve was found to be shifted down with respect to the branch GH. Therefore this branch cannot be interpreted as a continuation of GH.
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