Journal of Physics of the Earth
Online ISSN : 1884-2305
Print ISSN : 0022-3743
ISSN-L : 0022-3743
Volume 33, Issue 1
Displaying 1-3 of 3 articles from this issue
  • Shingo YOSHIDA
    1985 Volume 33 Issue 1 Pages 1-20
    Published: 1985
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Spontaneous propagation of an anti-plane shear crack is studied using Irwin's fracture criterion. We obtain the numerical solution of crack tip loci and slip motion when the critical stress intensity factor Kc and the dynamic stress drop Δσd are non-uniformly distributed on a fault plane. When rupture prop-agates along a fault plane with a localized high Kc region, the rupture process is divided into three stages. In the first stage, the rupture smoothly propagates with the radiation of elastic waves. In the second stage, when the rupture front reaches the high Kc region, the slip motion is decelerated and the radiated elastic wave is weakened. In the third stage, after the crack tip passes the high Kc region, the slip motion is accelerated again and the intensity of radiated wave increases. This gives a possible interpretation of multiple shock events. In Irwin's criterion, the rupture cannot propagate beyond the high Kc region leaving behind an unbroken area. The rupture process controlled by Griffith's fracture criterion is also studied. The rupture process in Griffith's criterion is similar to that in Irwin's criterion, except that the rupture velocity and the radiated seismic wave energy are somewhat greater than the case of Irwin's criterion.
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  • Takaya IWASAKI
    1985 Volume 33 Issue 1 Pages 21-43
    Published: 1985
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    In this paper, we treat quasi-static deformation field due to a dislocation source in a composite medium which consists of elastic layers overlying a strat-ified viscoelastic half-space. The rheologies of the viscoelastic layers are as-sumed to be elastic dilatational and Maxwell deviatoric. Integral representa-tions of the surface displacements are derived from those in the associated elastic problem by applying the correspondence principle of linear viscoelastici-ty. The effect of gravity is taken into account by modifying the boundary con-ditions with respect to normal stress.
    Features of the viscoelastic displacements are investigated for a three-layered structure model composed of an elastic surface layer, an intervening low viscosity layer, and a viscoelastic substratum with relatively high viscosity. A dislocation source is supposed to be located in the elastic surface layer. The effect of the stress relaxation in the substratum is examined for both a point source and a dimensional fault. Difference in the viscosity of the substratum affects the amount and extent of the viscoelastic deformation. In a model with a low viscous substratum, the amount of displacement is large and the deformation spreads in a broad area. The effect of gravity is investigated assuming a pure dip-slip fault. The viscoelastic deformation for the gravitating case is restrained in amount and extent as compared with the non-gravitating case. Such an effect of gravity becomes notable with time. In the gravitating case, the stress relaxation progresses fast, and the apparent relaxation time of deformation is much shorter than that for the non-gravitating case.
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  • Hiromi FUJIMOTO, Yoshibumi TOMODA
    1985 Volume 33 Issue 1 Pages 45-58
    Published: 1985
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    As the first step of developing a compact surface ship gravity meter, a compact gravity data processing system on-Iine with a Tokyo Surface Ship Gravity Meter (T.S.S.G.) was newly designed and tested at sea. This system was made compact by using a single board computer for gravity computations, a handhold personal computer for data recording, and a Loran C receiver for navigation. Free-air anomalies are obtained by this on-line processing. Over-all accuracy of this data processing is estimated to be 2-3 mgal; if the error from the Eötvös correction is not considered, the accuracy is estimated to be 0.1 mgal. The data processing system was successfully tested on board a research vessel and used for the gravity measurements around Japan in the case of the Japan-France Cooperative Project "KAIKO."
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