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Volume 22 (1976)
- Issue 4 Pages 201-
- Issue 3 Pages 139-
- Issue 2 Pages 65-
- Issue 1 Pages 1-
Volume 22, Issue 3
Displaying 1-7 of 7 articles from this issue
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Yoichiro FUJII1976 Volume 22 Issue 3 Pages 139-148
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA cycle of vertical crustal movement before and after the Ito earthquake swarm, that was active during the period from February to November 1930 in the eastern part of Izu Peninsula, Japan, is thoroughly examined by using all results obtained through precise levelling across its epicentral region in order to investigate a validity of dilatancyfluid diffusion model for earthquake occurrence. Rapidly decaying subsidence followed at the inner part of upheaval area of the ground that was associated with the beginning of the earthquake swarm, while no remarkable subsidence could be recognized at the outer part of the upheaval area for a long duration after the earthquake swarm activity. Some permanent vertical displacement is still remained even for 40 years after the earthquake swarm. Upheaval and subsequent subsidence can be explained by dilatancy due to crack opening and dilatancy recovery due to crack closing. Furthermore, permanent static deformation of the crust supports an elastic dislocation model for the earthquake swarm. The author gives a synthetic model. Dilatancy developed along a future fault plane in the first stage causes local upheaval and slow dislocation movement in the second stage. After the earthquake swarm activity, dilatancy recovery causes subsidence and dislocation gives permanent displacement.View full abstractDownload PDF (893K) -
Hikaru DOI, Masaaki KATO, Yasuo WADA, Takeshi MIKUMO1976 Volume 22 Issue 3 Pages 149-159
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSCrustal movements have been routinely observed since 1966 at Kamitakara, which is located in the seismically active northwestern Chubu region, with three sets of quartztube strainmeters, two sets of water-tube tiltmeters and several sets of horizontal pendulum tiltmeters. The observed secular strains indicate remarkable variations during the period from late 1968 to early 1970, and also from mid-1974 to late 1975. These patterns seem consistent but sometimes in reverse sense with the strain changes at other two sites in the Chubu region, Tsukechi and Inuyama. The changes in the strain direction commonly observed at the three sites around the end of 1968 and those consistently identified in the tilt direction at Kamitakara and Inuyama, might be associated with pre-seismic movements to the central Gif u earthquake of 1969. It is also found that the strain and tilt rates at the above two sites change their direction after the earthquake, suggesting partial release of the accumulated strains there. The strain changes in 19741975, on the other hand, appear to reflect more widely-spaced crustal movements . Observations of the earth tidal strains show a gentle increase of tidal amplitude prior to the 1969 earthquake and decrease after the earthquake. More detailed discussion on the earth tidal observations will be made in a separate paper .View full abstractDownload PDF (1101K) -
Yukio OZAKI1976 Volume 22 Issue 3 Pages 160-164
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSSome results of comparison on analytical aerotriangulation procedure as a branch of geodetic surveyings are given to each step of conventional geodetic triangulation and analogue aerotriangulation. Several cautions on the treatment of the analytical aerotriangulation to the present methods performed in Japan, are necessary from the geodetic point of view, such as the procedures corresponding to station adjustment, side equation adjustment, in addition to the corrections for atmospheric refraction and the earth curvature in the conventional geodetic triangulation. To get further precise results by the analytical aerotriangulation, more rigorous treatments on calibration of comparator and observation of image should be required .View full abstractDownload PDF (583K) -
Hideo HANADA1976 Volume 22 Issue 3 Pages 165-177
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSContinuous observations of gravity change are being carried out by means of an Askania gravimeter Gs-12 (No. 193) in the Earthquake Research Institute, University of Tokyo. Data obtained are available for investigating not only tidal variations of gravity but also free oscillations of the earth ensued from great earthquakes . The present paper aims at investigating a spectral structure of the free oscillations of the earth by applying the maximum entropy method, which might be effective on spectral analyses even in the case that the magnitude of earthquake is not sufficiently great (M=7.47.7) and that the length of record is not sufficiently lnna s The accuracy and other characteristics of the method are also discussed in the present paper.View full abstractDownload PDF (1238K) -
Shiro OHKAWA, Izumi YOKOYAMA, Mikio SATOMURA, Ichiro NAKAGAWA1976 Volume 22 Issue 3 Pages 178-187
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA precise gravity measurement was carried out at 21 stations in the eastern part of the Hokkaido District in September 1975 by means of three LaCoste & Romberg gravimeters (G-31, 196 and 375). In recent years, precise gravity measurements have been repeated for the purpose of detecting gravity change accompanying the crustal movement and seismic activity in and around the Konsen Plain, where the ground has been subsiding at a rate of more than 1 cm/year before and after the earthquake off the Nemuro Peninsula on June 17, 1973 (M=7.4) which caused co-seismic ground subsidence of 5 to 10 cm in this region. Comparing the results of these measurements with each other, gravity change was calculated for the period of 1962 to 1975. The gravity change in the Konsen Plain between 1962 and 1973 which includes that accompanying the earthquake was negative contrary to that expected from the ground subsidence. The decrease amounting to 170 pgals, which are larger than the measure-ment error in 1962, is too large to be explained by either density decrease caused by the strain release associated with the earthquake or lowering of the ground water level. Along the Pacific coast of this region, sudden gravity decrease amounting to 100, ugals was observed in only one month between July and August 1973 immediately after the earthquake, whereas the result of the re-measurement in 1974 shows that the decrease was almost recovered within the succeeding one year. Between 1974 and 1975, no sig-nificant gravity change could be detected, because most of the change was less than 20 pgals. Some mechanism was examined for interpreting the abrupt gravity decrease immediately after the earthquake and its recovery observed between 1973 and 1974, but any reasonable one is not yet found. To give a definite answer to the question whether such post-seismic gravity change is due to real phenomena or not, more detailed consideration and regular repetition of precise gravity measurement should be made in future.View full abstractDownload PDF (908K) -
Ichiro NAKAGAWA1976 Volume 22 Issue 3 Pages 188-191
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSThe development of a portable gravimeter of spring type enables gravity measurements to be made more easily, rapidly and accurately, and as a result, it is highly expected that repeatedly precise gravity measurements are very useful for the purpose of earthquake prediction. Precise gravity measurements have repeatedly been carried out several times in the area around Lake Biwa-ko since 1950 in order to detect, if possible, the secular change of gravity. The results obtained so far show that gravity change observed on the west levelling line around the Lake Biwa-ko during the period of 19711975 was in excellent harmony with that presumed from the results of levelling surveys in the tendency, but the amount of the former was about a few times greater. The present results suggest that repeatedly precise gravity measurements may be substituted for levelling surveys as a rapid and economical way with less accuracy.View full abstractDownload PDF (572K) -
Yukio HAGIWARA1976 Volume 22 Issue 3 Pages 192-193
Published: December 25, 1976
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSTSUBOKAWA proposed a relation between earthquake magnitude and precursor time based on land-deformation data. In the present paper, probability functions of precursor time are derived from the Tsubokawa relation. It is also shown that this probability model is incompatible with a Weibull distribution.View full abstractDownload PDF (201K)
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