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Volume 25 (1979)
- Issue 4 Pages 261-
- Issue 3 Pages 185-
- Issue 2 Pages 71-
- Issue 1 Pages 1-
Volume 25, Issue 1
Displaying 1-9 of 9 articles from this issue
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An Interpretation of Anomalous Crustal Movement and Migrating Crustal MovementYoichiro FUJII1979 Volume 25 Issue 1 Pages 1-9
Published: June 25, 1979
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESS3 cm of crustal upheaval during March 1973-June 1977 near Kamogawa relative to Futtsu in the Boso peninsula, Chiba Prefecture, Japan was revealed by the precise levellings. The upheaval may be related with the earthquake swarm activities off the eastern part of the Boso peninsula approximately during the same period. These crustal activities are interpreted by an idea of accelerating plate subduction at the depth. Along the extension of the seismic fault plane that was reptured during the 1703 Genroku Kanto earthquake and is locked after the eathquake, the following aseismic reverse faulting is assumed;strike of fault N45°E, length of fault 40 km, width of fault 30 km, dip angle 70°, depth of center of fault plane 28.2 km, left-lateral slip 5.1 cm, reverse slip 14.1 cm.The crustal movement deduced from the assumed model can account for the observed crustal movement. Similar crustal upheaval occurred in 1969 and migrated to NNW direction afterwards. This migrated upheaval is interpretated by the following aseismic reverse faulting at the deeper extension of the Sagami-bay fault;strike of fault N50°E, length of fault 20km, width of fault 30km, dip angle 30°, depth of center of fault plane 32.5km, right-lateral slip 6.3cm, reverse slip 13.6cm.View full abstractDownload PDF (2290K) -
Yukio HAGIWARA1979 Volume 25 Issue 1 Pages 10-19
Published: June 25, 1979
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSAs one of members of the Seismological Mission to the People's Republic of China, the author has the opportunity to contact with Chinese researchers for gravity change. In China, repeated gravity measurements have been made for monitoring preseismic changes in gravity since the 1966 Xingtai earthquake . The purpose of this paper is to introduce the gravity-change results obtained for the 1975 Haicheng, the 1976 Songpan Pingwu and the 1976 Tangshan earthquakes. Inf ormations concerning with the Songpan Pingwu earthquake have not so much been given outside China . The gravity change there has the general tendency to appear in the extensive areas surrounding the epicenter. The preseismic gravity change is sometimes found even in areas of 200 km distant from the epicenter. Another feature is that the maximum change amounts to a few hundred?Egals, sometimes ten times larger than what is expected from free-air rate. Possible cause of such a large and wide change lies in the fact that the continental crust is geologically uniform with large-scale faults . In order to check instrumental differences, if any, the mutual field comparison should be made between worldwidely-used LaCoste and Romberg gravimeters and the gravimeters used in China.View full abstractDownload PDF (896K) -
Hideo HANADA, Ichiro MURATA, Michio YANAGISAWA1979 Volume 25 Issue 1 Pages 20-25
Published: June 25, 1979
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSThe absolute measurement of gravity was carried out at the Aburatsubo Crustal Movement Observatory for the period from December 5 to December 13, 1978. The principle of measurement adopted here is the simple free fall with the falling distance of 30 cm. Using a cat's eye as a falling object, a Michelson interferometer measures the falling distance with the wavelength of a He-Ne laser beam as a length standard every 1 ms. The interference fringes are recorded on a film. Ground vibrations during dropping of the falling object are also observed by making use of a long period up-down seismometer. The gravity value obtained from thirty-five drops is, gABS=979774.984±0.083 mgal.Furthermore, the ground vibration corrections are made for these data, and the result is, gABS=979774.924±0.044 mgal.On the other hand, the gravity value there referred to JGSN 75 is, gABS (JGSN 75) =979774.997 mgal. The difference between these two values is about 70 μgal, and this seems to be mainly caused by the incompleteness of ground vibration correction.View full abstractDownload PDF (3797K) -
Katsumi NAKANE, Yoichiro FUJII1979 Volume 25 Issue 1 Pages 26-37
Published: June 25, 1979
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSThere has been no reliable or systematic evaluation of the old triangulation network in the Kanto district. The authors newly adjusted the old second order triangulation network in the Izu district following the previous report which gave the results of reevaluation of the old second order triangulation network in the Kanto district. From these data the authors have calculated the earth's strain for each epoch. The fact that the polarity of principal axes of the strain were reversed by the earth quakes in the south Kanto district is found as a result of investigating the change of the axes. The regions where the strain axes were reversed correspond to aftershock regions of the 1923 Kanto earthquake (M7.9), the 1930 Kita-Izu earthquake (M7.0.), the 1974 Off-Izu Peninsula earthquake (M6.9) and the 1978 Izu-Oshima-Kinkai earthquake (M7.0) respectively. In the south Kanto district there are few area where high accumlated strain is found. The earthquake with magnitude larger than 7.0 may not occure in the discussed region in near future.View full abstractDownload PDF (1230K) -
Masaaki KATO, Makoto KOIZUMI, Yoshinobu HOSO, Torao TANAKA, Yutaka TAN ...1979 Volume 25 Issue 1 Pages 38-48
Published: June 25, 1979
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSSecular changes of the ground tilts and strains observed at Yura, Wakayama Prefecture, since the beginning of observations in 1951 are reviewed. Anomalous tilts which have been considered to be related with two large earthquakes, the 1952 Yoshino and 1960 Odaigahara earthquakes, are especially conspicuous in the whole period of the observations. However, there still remains a possibility that these changes might contain instrumental drift to some degree. A change of the mode of the tilts and strains is seen in the period from 1973 to 1974, which might be caused either by the occurrence of two remarkable earthquakes (M=5.9 and 5.8) about 25 km east of Yura, or coincident with an anomalous crustal deformation over a wide area observed at several other stations in Japan.View full abstractDownload PDF (3598K) -
Warren WHITE, Keiichi HASUNUMA, Gary MEYERS1979 Volume 25 Issue 1 Pages 49-55
Published: June 25, 1979
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESS -
Yukio HAGIWARA1979 Volume 25 Issue 1 Pages 56-57
Published: June 25, 1979
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESS -
Yoichiro FUJII1979 Volume 25 Issue 1 Pages 58-60
Published: June 25, 1979
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSThe 2nd order triangulation net covering the Seven Izu Islands is re-evaluated and the result is compared with the new result of side length measurements. The calculated earth's horizontal strain during last 80 years between the Izu Penin sula and the Ooshima is compatible with the NNW drifting of the Philippine Sea Plate.View full abstractDownload PDF (299K) -
Ichiro MURATA1979 Volume 25 Issue 1 Pages 61-62
Published: June 25, 1979
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSVertical gradients of gravity in horizontal tunnels are analytically calculated for the pur-pose of investigating their effects on absolute measurements of gravity. It is found that the tunnel with circular cross-section has uniform vertical gradient of 2πGρ within the tunnel, and that the distribution of vertical gradient in the square shaped tunnel has the form of
∂F/∂z=2Gρ(arctan a-ξ/b-ζ+arctan a+ξ/b-ζ+arctan a-ξ/b-ζ+arctan a+ξ/b+ζ),
in addition to the normal gradient in the crust; free air gradient -4πGρ. The value of 2πGρ when ρ=2.5 g/cm3 is 105 μGal/m and cannot be neglected in the instrumental height correction.View full abstractDownload PDF (229K)
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