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Volume 16, Issue 3
Displaying 1-9 of 9 articles from this issue
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Tomowo HIRASAWA, Ryosuke SATO1963 Volume 16 Issue 3 Pages 87-100
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSRecently, measurements of the specific dissipation factor, Q, have been made not only for body waves, but also for surface waves, according to developments of observationall techniques. For instance, Y. SATÔ (1958) studied G-waves by means of Fourier analysis and found that Q for G-waves depends on frequency. The velocity of surface waves generally depends upon frequency and structures of the medium under consideration. Therefore, even if Q for body waves is independent of frequency, it is natural to consider that Q for surface waves depends not only on frequency and velocity distribution but also on distribution of Q for body waves in the medium.
In this paper, assuming that Q for body waves is independent of frequency and using the equation of motion in low loss medium proposed by L. KNOPOFF (1956), the apparent frequency dependence of Q for surface waves is investigated in the following two cases.
First, the frequency dependence of Q for Love waves (QL) in a layered medium, in which Q's for shear waves are Q1 in the layer and Q2 in the substratum, respectively, is investigated. In this case, it is, as was expected, found that QL varies with period even when Q for body waves is constant throughout the medium (Q1=Q2). QL generally tends to Q1 and Q2 as the period of Love waves tend to zero and infinity, respectively, as well as the velocity of Love waves tends to shear velocities in the layer and the substratum for both limits of periods. When Q2 is larger than Q1, and even when Q2 is, strictly speaking, a little smaller than Q1, QL has a minimum value for a certain period which tends to zero as the ratio of Q2 to Q1 becomes very large.
Second, the frequency dependence of QL or QR (for Rayleigh waves) in a semi-infinite medium, in which the velocity of body waves and Q for body waves vary linearly withh depth, is studied by using the variational methods. It is shown that the longer the period is, the smaller QL or QR is even when Q for body waves does not vary with depth.View full abstractDownload PDF (1003K) -
Hiroshi TSUDA, Hitoshi TAKEUCHI1963 Volume 16 Issue 3 Pages 101-105
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA trial was made to determine the maximum rigidity of the earth core μc compatible with observations of free torsional ocsillations of the earth. A normalized free oscillation mode method was used to pick up an oscillation of the minimum total kinetic energy for each μc The maximum allowable rigidity of the earth's core thus determined is 1012dyne/cm2.View full abstractDownload PDF (382K) -
Hitoshi TAKEUCHI, Masanori SAITO, Naota KOBAYASHI1963 Volume 16 Issue 3 Pages 106-114
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDispersion curves for second mode mantle Rayleigh and Love waves are obtained for the following five earth models; Jeffreys, Gutenberg, Lehmann, 8099 and a new model denoted by Lehmann*. Results for the Love waves agree well with those obtained by Jobert and Satô and others. There is, however, a significant difference for the Rayleigh waves of periods shorter than 70sec between our results and those by Bolt and others. A discussion is made on what this difference is due to.View full abstractDownload PDF (662K) -
Yasuo SHIMAZU, Yoshiteru KONO1963 Volume 16 Issue 3 Pages 115-122
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSUnsteady thermal convection within the upper mantle is studied in connection with the hypothesis that a trigger to generate tectogenesis is the undulation of isotherm at the ocean-continent boundary area. It is emphasized that there are two types of convection which are different each other in physical conditions. Calculations are performed until the time of 200 million years from the start of the convective movement for the cases with kinematic viscosity ν=5×1021 and 1022cm2/sec. The maximum tangential stress at the upper boundary of the convective layer reaches 3×107dyn/cm2. It is unlikely that either fissure or fault is produced in the crust by such a convection.View full abstractDownload PDF (670K) -
Haruo MIKI1963 Volume 16 Issue 3 Pages 123-132
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSOnly the earthquakes of normal depth in the seismological reports issumed by the five stations in Japan during the I. G. Y. are used. The gradient of time-distance curve of seismic P wave is estimated directly from the observations, not from the smoothed curve of t-Δ.
The difference of arrival times due to the characteristics of seismometers and the foundations of stations are considered by reducing them to the standard instrument and station.
The earthquakes near the bisector of any pair of stations are rejected from the calculation, because the indefinite determinations of epicenters of these earthquakes bring about considerable errors to the result. Errors of dt/dΔ due to the focal depth, distance interval (dΔ), and the reference time-distance tables are also considered.
Comparison of stations.
Finally, calculated values from each earthquakes are superposed. But the earthquakes adopted at this stage are restricted to the ones near the great circle which involves Honshu (Japan), in order to avoid the errors due to the indefinite determinations of epicenters relative to the pair of stations.View full abstractDownload PDF (797K) -
Kazuo HAMADA1963 Volume 16 Issue 3 Pages 133-144
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSExperimental studies of surface waves are carried out, for a model which is shown in Fig. 1, by means of ultra-sonic techniques.
The relation between periods and amplitudes, when the layer thickness alone is varied, are investigated in the experiments.
In all cases, two wave trains are evident in the waves observed. One of two wave trains contains the waves having the maximum amplitude in all wave trains, its phase velocity is nealy equal to the shear velocity in the layer and its group velocity is smaller than that of RAYLEIGH waves in the layer. These wave trains have the periods that are shorter than that correspond to the minimum group velocity, the period correspond to the maximum amplitude is expressed by TVpl/H≈2.5, where T, Vpl and H indicate the period, the longitudinal velocity in the layer and the layer thickness respectively.
Another wave trains appear at the time expected by refracted P waves, its phase velocity is almost equal to the longitudinal velocity in the lower medium. This wave trains have the period expressed by TVpl/H≈3.
The waves, of which the phase velocity is equal to the shear velocity in the layer, correspond to the fundamental mode of RAYLEIGH waves.
Another waves, of which the phase velocity is almost equal to longitudinal velocity in the lower medium, is suspected to be complex roots in case of the normal mode solution.
The trains of these two waves are observed to lengthen as the epicentral distance increases.
The two wave trains do not change in phase velocity as well as group velocity, whereas they change in periods in proportion to the thickness of the layer when layer thickness varies.View full abstractDownload PDF (4857K) -
Cases of Separable Coordinates for Laplace's EquationTatsuo USAMI1963 Volume 16 Issue 3 Pages 145-148
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe equation of equilibrium of a homogeneous and isotropic elastic medium is solved for the orthogonal curvilinear coordinates of two dimensions under the condition that Laplace's equation is separable. Coordinates systems satisfying these conditions are Cartesian, cylindrical, elliptic cylindrical and parabolic cylindrical ones.
First, solutions of equation of motion is obtained. Then, making frequency in these solutions to zero, the equation of equilibrium is solved.View full abstractDownload PDF (242K) -
Mitsuo KEIMATSU1963 Volume 16 Issue 3 Pages 149-160
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThere are numerous historical records telling about the overflow of the sea in China. But most of them are concluded to have occurred by wind, and very few of them to have been caused by the earthquakes. I have found with difficulty no more than six records of tidal waves among many historical documents covering over 2, 000 years. The first occurred in Lai-chou Bay _??__??__??_ of Shan-tung Peninsula _??__??__??__??_, in the year 173. The second, at Chia-ting Hsien _??__??__??_, Lo-tien Chên _??__??__??_, Pao-shan Hsien _??__??__??_, facing the mouth of the river Yang-tse _??__??__??_, in 1509. The third, at three Hsiens _??_, Ch'êng-hai _??__??_, Ch'ao-yang _??__??_ Chieh-yang _??__??_, in Kwang-tung Province _??__??__??_, in 1640. The fourth in 1670, at the same places as in the year 1509. The fifth, at Chi-lung _??__??_, Formosa A _??__??_, in 1867. The last, at T'ung-an Hsien _??__??__??_, Fu-kien Province _??__??__??_, in 1917. See the map on p. 160.View full abstractDownload PDF (1459K) -
Michio OTSUKA, Shoji ISHIZUKA1963 Volume 16 Issue 3 Pages 161-162
Published: September 30, 1963
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (242K)
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