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Volume 21 (1975)
- Issue 4 Pages 179-
- Issue 3 Pages 131-
- Issue 2 Pages 75-
- Issue 1 Pages 1-
Volume 21, Issue 3
Displaying 1-5 of 5 articles from this issue
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Naosuke SEKIGUCHI1975 Volume 21 Issue 3 Pages 131-141
Published: January 25, 1976
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe latitude variations of the time interval between 1830 and 1860, based on the ancient observations, are studied. Only the materials which passed reliability tests are used, and reduced under the assumption that the ancient observations often contain large annual errors. The variations in the Chandlerian frequency and the semi-amplitude of this component are investigated. It is found that the mean Chandlerian frequency has a large value of (423.3)-1±0.68×10-5 (mean solar day)-1 during this interval compared with those of the modern observations, while the semi-amplitude has a minimum value 0″.072±0″.014 about 1845. These features are very similar to those around 1930.View full abstractDownload PDF (1019K) -
Fumiaki KIMATA, Tsuneo YAMAUCHI, Mamoru YAMADA1975 Volume 21 Issue 3 Pages 142-149
Published: January 25, 1976
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSThe detecting horizontal strain accumuration with electro-optical means, three geodetic networks; namely Hamanako network (HMN), Atsumi network (ATM) and Kamiyahagi network (KMY), had been set up in the Mikawa region . Since 1972, the authors have been repeating measurement with a Geodimeter model 6 every year . During the tree years survey period from 1972 to 1975, considerably large strains, coparing to some observational errors due to incompleteness of the atmospheric correction or setting of the instrument and so on, have been observed. If these results may be ragarded as significant signals of the ground deformation, the folling conclusions can be noticed: The principal axis of cotracti axis of contraction is in the E-W direction at the Kamiyahagi network, about 60 km inland from the Enshunada coast. On the other hand, ones at the Hamanako network and Atumi network which are located on the coast, are in the NNW-SSE direction. These azimuths of contraction are concordant with the seismic force system of the shallow earthquakes in this region. Strain rates amounting to 20-40×10-6 in the three years period are about twenty times larger than ones obtained from the precies triangulation data in the period from 188596 to 1973.View full abstractDownload PDF (2043K) -
Tsuneji RIKITAKE1975 Volume 21 Issue 3 Pages 150-158
Published: January 25, 1976
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSRelationship between precursor time and earthquake magnitude is examined for tilt and strain precursors amounting 112 in number. No dependence of precursor time on magnitude is found for precursors as observed with horizontal pendulum type tiltmeters and strainmeters. However, logarithmic precursor time seems to be linearly correlated to magnitude for precursors observed with water-tube tiltmeters. On the basis of the logarithmic precursor time vs. magnitude plot for precursors excluding tilt, strain and foreshock, two types of precursors are pointed out. The type-I precursors occur several hours prior to the main shock, their precursor time being ap proximately constant regardless of the magnitude of the main shock. The precursor time (T) of the type-II precursor are correlated to the magnitude (M) in a linear fashion aslog10 T=0.76M-1.83in which T is measured in units of days. The nature of these two types of precursors suggests a practicable strategy of earth quake prediction along with the earthquake statistics and monitoring of crustal strain.View full abstractDownload PDF (806K) -
Akira YAMAZAKI1975 Volume 21 Issue 3 Pages 159-169
Published: January 25, 1976
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe establishment of marine geodetic control is very significant not only for geodetic work but also for various scientific investigations in the oceans. Recently some attempts have been made to establish the geodetic control points on the ocean floor. Among those, it is reported that the system being consist of three acoustic transponders is very effective for practical use. However, the presently used technique for determining the transponder geometry requires that the accurate ship positions are needed to be determined in advance by using a land-based-precise positioning system. Consequently, this technique can not be used when the position of the ship is not accurate, for example, when the ship is far from the coast. In this report, a new technique is proposed which determine the transponder geometry by only acoustic ranging data without the knowledge of the ship position. The observation equation is derived from the condition that the projection vectors of three slant ranges on the sea surface lie always in the constant plane (sea surface). Based on some assumptions, the accuracy of the transponder geometry is estimated as about 1 meter for ranging accuracy of 10 at 3000 meters depth. The use of this technique in conjunction with NNSS will make it possible to deter mine the geodetic positions in the oceans with an accuracy almost comparable to that of positioning on land, even in such region that land-based-precise positioning systems are not available.View full abstractDownload PDF (1191K) -
Naokichi KIKUCHI1975 Volume 21 Issue 3 Pages 170-178
Published: January 25, 1976
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe excitation functions for the Earth's polar motion due to the variation of the atmos pheric pressure distribution are calculated from the three kinds of materials, labeled here by A, B and C, of the meteorological data which were published by the Japan Meteorological Agency. The material A has the normals of the monthly atmospheric pressure at the mean sea level for both of the northern and southern hemispheres. Its average year values in latitude range 80°N-0° are taken over the period 1881-1935 and those in latitude range 0-60°S over the period 1931-1960. The material B has the average year values of the monthly atmospheric pressure in the northern hemisphere (80°N-10°N), which are taken over the true periods 1909-1914 and 1924-1937. The material C includes the monthly mean values of the atmospheric pressure at the mean sea level and the height of the isobaric surface of 500 mb from 1947 Mar. to 1975 Feb. in the northern hemisphere with mesh interval 10° in both of latitude and longitude. It turns out that the excitation function can be fairly described by the data of the atmospheric pressure on only the northern hemisphere. The amplitude of the annual component of the excitation function shows the secular variation with the rate of 0.1610×100 radian/yr.. The turning points of the annual change in summer appear almost stationarly on July, but the turning point in winter varies from year to year ranging from November to February and the double peaks appear over about one third of years with data. The differential excitation function on each latitude zone with mesh 10° shows irregular variations at the higher latitude zone while stable annual changes at the lower latitude zone. It is, however, at the intermediate latitude zones that the amplitude of the annual component and the irregular variations are large. It is shown that the atmospheric pressure change gives rise to the annual term in the polar motion of the order of 0″.l with its secular variations of 0″.01.View full abstractDownload PDF (951K)
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