Journal of Physics of the Earth
Online ISSN : 1884-2305
Print ISSN : 0022-3743
ISSN-L : 0022-3743
Volume 27, Issue 3
Displaying 1-4 of 4 articles from this issue
    1979 Volume 27 Issue 3 Pages 171-187
    Published: 1979
    Released on J-STAGE: January 25, 2010
    The energy balance of earthquake fault motions is analysed, and expressions for seismic energy and seismic efficiency are derived in terms of physical quantities at the seismic source, such as initial stress, sliding frictional stress, rupture velocity and so on. In this paper an antiplane strain crack model is employed.
    It is shown that shallow strike-slip earthquakes will have very low seismic efficiency. Seismic wave energy, calculated on the basis of the crack model proposed in this paper, is generally smaller than that expected from the Gutenberg-Richter relation by about an order of magnitude. If the rupture velocity is approximately equal to shear wave velocity, we get the expression for seismic wave energy Es,
    where L, W, μ, and Δσ are fault length, width, rigidity and stress drop on the fault surface respectively. The above expression can be employed as a rough estimate of the seismic wave energy.
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  • Eiji OHTANI
    1979 Volume 27 Issue 3 Pages 189-208
    Published: 1979
    Released on J-STAGE: April 30, 2009
    The melting relations in fayalite Fe2SiO4 and its high pressure modification γ-Fe2SiO4 have been experimentally studied at pressures up to about 200kbar. Fayalite melts congruently up to the triple point, 70±5kbar and 1, 520±25°C, of fayalite, γ-Fe2SiO4, and liquid. The initial slope of γ-Fe2siO4 is about 12°/kbar. γ-Fe2siO4 melts congruently up to about 130 kbar, above which it melts incongruently into stishovite SiO2 and liquid. The incongruent melting in γ-Fe2SiO4 terminates at about 170kbar and 2, 200°C. Above this pressure, the melting mode switches to the eutectic melting between wustite Fe1-xO and stishovite SiO2, which are the post γ-Fe2SiO4 assembly. The present data suggest a possibility of incongruent melting of γ-(Mg, Fe)2SiO4 at high pressure. Possible roles of the change in melting mode on the chemical fractionation of the earth's mantle are discussed.
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  • Yoshio SUMINO
    1979 Volume 27 Issue 3 Pages 209-238
    Published: 1979
    Released on J-STAGE: April 30, 2009
    Elastic constants of single-crystal Mn2SiO4, Fe2SiO4 and Co2SiO4 olivine are measured by the rectangular parallelepiped resonance (RPR) method at temperatures between 20° and 400°C. Elastic constants Cij (Mbar) and their temperature derivatives ∂Cij/∂T (kbar/deg) are:
    The isotropic properties, density ρ, adiabatic bulkmodulus K3, rigidityμ, the Poisson's ratio σ, and their temperature derivatives calculated by the Voigt-Reuss-Hill scheme are:
    By combining the present results with the previous data on a magnesium rich olivine, the effect of cation substitution on the elastic properties of olivine group minerals is discussed and the elastic constants of olivine at high temperature in the earth's mantle are clarified.
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  • Tamao SATO
    1979 Volume 27 Issue 3 Pages 239-253
    Published: 1979
    Released on J-STAGE: April 30, 2009
    The P-wave velocity in the crust beneath the Northeastern part of Honshu, Japan, is estimated by using the arrival-time data of initial P waves from local earthquakes. To determine simultaneously hypocenter parameters, station corrections, and the parameters of the velocity model, the least-squares method developed by Crosson is applied to two different data sets. Firstly for the data set consisting of all of events well beneath the land, the estimated velocities are 6.0-6.1km/s for the upper 12km of the crust, and 6.3-6.4km/s for the intermediate crust between 12-and 20-km depths. The velocity of the lower crust remains unsolved since it depends on the Moho depth assigned. If the Pn velocity is assumed to be 7.53 km/s as previously obtained for the Kesennuma-Oga profile, however, some restrictions are put on the velocity of the lower crust; it would be 6.6km/s or greater if the Moho depth is greater than 33km. A low-velocity zone would be present in the lower crust if the Moho is positioned at a depth of 30km or less. Secondly for the data set consisting partly of events located within a narrow zone near the Aseismic front, the inverted velocities for the upper and intermediate crusts are similar to those for the first set. However, the inverted velocity of the lowermost half space is 7.8km/s, a value appreciably greater than 7.53km/s. This result indicates that the velocity for the very upper mantle just beneath the Aseismic front is at least greater than 7.8km/s. Although the change of Pn velocity from 7.7 to 8.1km/s may take place at the Aseismic front, a low Pn velocity of 7.53km/s seems to take place a few tens of kilometers to the west of it.
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