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Volume 16 (1968)
- Issue 2 Pages 45-
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Volume 16, Issue 2
Displaying 1-5 of 5 articles from this issue
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Ryosuke SATO1968 Volume 16 Issue 2 Pages 45-54
Published: 1968
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSVariation of amplitudes of body waves with epicentral distance is investigated. The amplitudes are much sensitive to velocity distribution within the earth than the travel-time curves. If the ray touches a boundary where the velocity is continuous but its gradient is discontinuous, the amplitudes at the surface show a drastic change due to the discontinuity. When both the velocity and its gradient are continuous, the variation of amplitudes is closely related to the variation of the second derivative of the velocity with depth. These imply that amplitude analysis in addition to travel-time analysis may give us detailed information about fine structure of the earth's interior.
When obtaining a smooth amplitude-distance curve by dividing the earth into many heterogeneous spherical shells where the velocity distribution by Bullen's law is assumed in each shell, thickness of about 200km gives rough but enough information when the deepest point of the ray is in the shell where the velocity varies slowly. For the ray whose deepest point is in the shell where the velocity varies largely, it is necessary to take much thinner shell, for example, in the C region, thickness of at least 20km is required.View full abstractDownload PDF (1107K) -
SH WavesRyosuke SATO1968 Volume 16 Issue 2 Pages 55-59
Published: 1968
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSExpressions of disturbances due to a point source of SH torque in a homogeneous sphere with a liquid core can be found without any assumption. From numerical computations of the exact solutions near geometrical shadow boundary, empirical expressions for the following quantities in the wide frequency range are obtained; amplitude corrections for diffraction in the lit zone and frequency dependence of amplitude of diffracted waves in the shadow zone.View full abstractDownload PDF (563K) -
Tuneto KURITA1968 Volume 16 Issue 2 Pages 61-78
Published: 1968
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSQ for short-period P-waves in the mantle has been investigated, based on the spectral analysis of the initial P phases of two earthquakes. Amplitude spectrums in the epicentral range between 21 and 103 degrees have been calculated, compensating for the propagation effects through the total seismic path. Amplitude-distance relations over the frequency range between 0.3 and 1.3cps show that the rate of diminution of amplitude with epicentral distance is independent of frequency. From this observational results it follows that the intrinsic Q value becomes greater with depth between about 700 and 2500km, and also with increasing frequency. The frequency independency of Q theory is inappropriate within the frequency range between 0.3 and 1.3cps. It is also shown that the source asymmetry is not masked by the propagation effects except the stations near the nodal line for these frequencies.View full abstractDownload PDF (2381K) -
Ilkka NOPONEN1968 Volume 16 Issue 2 Pages 79-85
Published: 1968
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSMulticomponent recordings of P-wave groups from 4 underwater explosions in the Baltic Shield are processed to study the possibility of utilizing the particle motion in the interpretation of records from near events. Several of the phases predicted by a crustal model for the area could be found and identified by correlating the vertical with the radial component and by calculating the incidence angle. Phases probably originating from below the Moho were also detected. Although some of these impulses could be observed in the original traces, they could not be identified without knowledge of the source and travel times. It is concluded that the reliability of the detection and identifi-cation of phases can be increased by taking the correlation of the vertical and radial components and by calculating the incidence angle.View full abstractDownload PDF (1385K) -
Takeshi MIKUMO, Ichiro NAKAGAWA1968 Volume 16 Issue 2 Pages 87-96
Published: 1968
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSThe spectral structure of the earth tides which have been observed during one year by an Askania gravimeter at Kyoto, and that of the corresponding theoretical tides on a rigid earth, were compared to determine the tidal factor of gravity and the phase lag with a high precision. A band-pass filter that has dominant responses only for semidiurnal or diurnal frequencies was applied to both of the tidal functions, to eliminate the effects of drift and of contamination from other constituents. Variations in the two tidal parameters during the period were also examined, extracting only M2 or O1 wave by the use of a narrow Gaussian filter. These results show long-period fluctuations with several months, suggesting a limit for discussions on elastic and anelastic behavior of the earth.View full abstractDownload PDF (1197K)
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