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Volume 38 (1992)
- Issue 4 Pages 315-
- Issue 3 Pages 211-
- Issue 2 Pages 89-
- Issue 1 Pages 1-
Volume 38, Issue 1
Displaying 1-6 of 6 articles from this issue
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Tsuneo YAMAUCHI, Mamoru YAMADA1992 Volume 38 Issue 1 Pages 1-6
Published: March 25, 1992
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA variable capacitance type water-tube tiltmeter has been designed for continuous observations of crustal deformation. Its sensor consists of a capacitance between the water surface of a vessel and a metal plate existing above the water surface. Watertube tiltmeters have ordinarily used a sensor attached on a float, and tilt records of these instruments have contained steps caused by mechanical troubles caused by the supporting system of the float. The newly designed tiltmeter has not the mechanical supporting system so that the instrument operates well without troubles at the time of large earthquakes. The electrical circuit of this tiltmeter is simple and inexpensive. The signal is accurate enough for observing ground tilt, and stable for use over long periods.View full abstractDownload PDF (2513K) -
Part 1. Vertical Crustal Movements Revealed by Geodetic DataIsao MINEMATSU1992 Volume 38 Issue 1 Pages 7-19
Published: March 25, 1992
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSRecent vertical crustal movements in Shikoku district, Japan, after the Nankaido earthquake in 1946 were investigated using both levelling and oceanic tidal data. The temporal and spatial variations of the movements were revealed. Cape Muroto has been subsiding at an almost constant rate since early in the period concerned, and a large upheaval was found in the southwestern Shikoku. This upheaval with a local subsidence around Cape Ashizuri showed an intermittent property, and it has intensively occurred in a few years after the earthquake. The variations clarified in the present study suggested that crustal movements in this region were hard to interpret in terms of a simple earthquake cycle model.View full abstractDownload PDF (1251K) -
Part 2. Graphic Representation in Time-Space DomainIsao MINEMATSU1992 Volume 38 Issue 1 Pages 21-27
Published: March 25, 1992
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSWe made an attempt to introduce a technique utilizing computer graphics so as to represent efficiently the temporal and spatial variations of vertical crustal movements in Shikoku district, Japan. This technique utilizes a packaged program called CGMS (Computer Graphics and Movie System) in graphic data processing. With this technique, oblique projections which represent spatial variations of the data can be seen with temporal variations as an animated cartoon. The interpolation techniques in time-space domains were those utilizing a spline function. A computer program developed was applied to the data of vertical crustal movements in Shikoku district, and the dynamic feature of the crustal movements in this region was demonstrated.View full abstractDownload PDF (2003K) -
Daniel B. ROSENBLATT, Seiichi SHIMADA, Yehuda BOCK, Jean B. MINSTER, D ...1992 Volume 38 Issue 1 Pages 29-44
Published: March 25, 1992
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSWe have examined the impact of the implementation of Selective Availability (SA) on GPS satellites on daily relative position estimates of the Permanent GPS Geodetic Array (PGGA) sites in southern California. The PGGA became operational in February 1990. Data are collected daily at Scripps Institution of Oceanography (SIO) and the Jet Propulsion Laboratory (JPL) from three Rogue SNR-8 receivers deployed at JPL, SIO, and Pinon Flat Observatory, and from three Mini-Mac 2816AT receivers at the CIGNFT tracking stations in California, Massachusetts, and Florida. The CIGNET stations are used as fiducial satellite tracking sites. There are two chief components to selective availability, 1) a pseudo-random clock dithering in the GPS carrier phase that is usually between 1-2 cycles per second. 2) Falsified broadcast ephemerides from the GPS satellites. Our study examined the effects of SA upon interferometric baseline measurement accuracy during the first application of selective availability from April to September of 1990. We found that as long as the simultaneity of observation time tags is maintained between receivers, SA alterations of the GPS signals do not degrade positioning accuracy when using several hours of doubly-differenced phase measurements. In fact, adding observations of the SA affected Block II satellites improved baseline repeatability (even in California where Block I geometrical coverage was quite favorable). However, we have learned that in 1990 SA had very adverse effects on networks with non-simultaneousobservations and made data editing more problematic.View full abstractDownload PDF (4085K) -
Koichiro DOI1992 Volume 38 Issue 1 Pages 45-61
Published: March 25, 1992
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSIn recent years, continuous observations of gravity with time have been achieved by employing superconducting gravity meters with long-term stability and high precision. As a result, even small gravity changes associated with atmospheric loading are now detectable. It is, therefore, possible to obtain information about the structure of the earth from signals caused by atmospheric loading. An attempt to estimate a load Green's function for gravity was performed using the gravity changes associated with time-varying atmospheric pressure loads. Model parameters corresponding to discrete load Green's functions were, at first, estimated by applying the conventional least squares method, but those absolute values were too large to be acceptable. A similar estimation by applying the non-negative least squares method was then performed. As a result, one parameter obtained for the nearest region was fairly well consistent with the theoretically predicted one. However, the other parameters could not be determined. The cause of such a result may be noises included in gravity changes associated with atmospheric pressure variations. It was found by a numerical experiment that reduction of noises to the level of about 10-5 pgal would be needed to estimate the parameters precisely. But it is practically impossible to reduce the noise to that level. Thus, reduction of noises such as the influence of underground water which will be a major source of observational noise and a potent method of inversion are required for the improvement of the result. The present method can be employed to estimate ocean response to atmospheric pressure variations. Furthermore, it is possible to apply the present attempt to a case of oceanic loading, if the change of sea level is accurately determined.View full abstractDownload PDF (2473K) -
Yuki KUROISHI, Masaki MURAKAMI, Masaru KAIDZU1992 Volume 38 Issue 1 Pages 63-74
Published: March 25, 1992
Released on J-STAGE: July 05, 2011
JOURNAL FREE ACCESSThe First-Order Gravity Network of Japan which consists of about 300 gravity stations plays an essential role in gravimetry in Japan . The network gives reference datum for all the gravity measurements . Since 1985, Geographical Survey Institute has been carrying out absolute gravity measurements at 12 stations with a Sakuma-type absolute gravimeter to improve the accuracy of the network. Results of absolute gravity measurements revealed that the precision and repeatability of absolute gravity values obtained were higher than 10μGals. Test adjustment of a part of the network showed that the precision of gravity values controlled by absolute gravity measurements is higher than 10 μGals. Gravity measurements in this network will be repeatedly performed at 5 to 7 year intervals together with geodetic leveling. With those measurements, gravity changes associated with vertical crustal movements of up to a few centimeters can be detected throughout Japan. The combination of precise gravity measurements with precise levelings is a powerful tool to clarify the underground physical process which causes vertical crustal deformation.View full abstractDownload PDF (1208K)
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