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Volume 43 (1997)
- Issue 4 Pages 213-
- Issue 3 Pages 133-
- Issue 2 Pages 33-
- Issue 1 Pages 1-
Volume 43, Issue 1
Displaying 1-3 of 3 articles from this issue
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Kosuke Heki1997 Volume 43 Issue 1 Pages 1-12
Published: March 25, 1997
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSPrecise positioning methods based on space techniques, such as VLBI (Very Long Baseline Interferometry) and SLR (Satellite Laser Ranging), which became available in 1980's, made it possible to directly measure the movement of tectonic plates which had never been verified by geodetic means. In the middle of 1980's, CDP (Crustal Dynamics Project) started as an international cooperation being conducted by NASA, and the data taken by now provided lots of new information on global plate motions . GPS (Global Positioning System) later became popular worldwide as a handy space geodetic tool, and complicated deformation of the plate boundary regions as well as the movements of smaller crustal blocks have been clarified. Plate tectonics has been viewed for the first time through geodetic time window by such measurements, and we found that the movement of the stable interiors of plates are constant over a wide range of timescales while instantaneous velocities of plate boundary regions fall somewhere between those of the two adjacent plates. Such observations are also clarifying the movements of microplates, such as the Amurian plate, that has been difficult to be determined by conventional methods e.g. ocean magnetic anomalies. In addition to interplate earthquakes and rifting episodes, we found that slow aseismic events play important roles in processes at convergent and divergent plate boundaries. It is expected that space geodeic observations with sufficient temporal and spatial density/coverage will elucidate the mechanism of such processes in the future.View full abstractDownload PDF (4420K) -
Koichiro Doi1997 Volume 43 Issue 1 Pages 13-21
Published: March 25, 1997
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA load Green's function for gravity is estimated by an inversion method employing gravity changes induced by atmospheric pressure loadings. The gravity data were derived from a superconducting gravimeter at Kyoto University . We introduce a theoretically estimated load Green's function as a priori data for calculating a minimum variance solution. A region from the observation point to 4° in angular distance is divided into four sub-regions, width of which is 1°. Parameters to be solved are average values of the unknown load Green's function of the four sub-regions . The parameters are estimated for two periods from December 1989 to February 1990 and from May 1990 to January 1991. The results for the two periods indicate good agreement with each other. In comparison with theoretical values, the results for the nearest region are consistent with the theoretically expected value and those for other regions have smaller absoulte values. Especially, the values for the farthest region are about 60% of the theoretically expected one. We did not take into account any assumption about the ocean response to atmospheric pressure changes in this estimation . Since most part of the farthest region is occupied by the ocean, the results will reflect small response of the ocean to atmospheric pressure changes. Residuals after removal of loading effects from input data decreased by using the observationally estimated results instead of the theoretical values. This means that the results provide a suitable load Green's function at the observation point .View full abstractDownload PDF (877K) -
Katsutada Kaminuma, Isao Kimura1997 Volume 43 Issue 1 Pages 23-26
Published: March 25, 1997
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSA route for repeat leveling survey was established in East Ongul Island (69°S, 39°E), East Antarctica by the 20th Japanese Antarctic Research Expedition (DARE-20) in 1979 and JARE-23 in 1982. The leveling measurements were repeated by JARE-37 in 1996. Because of the time limitation, only 2.3 km out of the total length of 5.3 km route was surveyed. The average square error, every one kilometer is obtained as ±0.57 mm. The Bench Mark (BM) 1040 is taken as the reference point which is also the reference point for oceanic tide observations at Syowa Station and is located on the westernmost point of the route. The height of BM 1040 is 2.3380 m. The vertical difference between the values by JARE-23 and JARE-37 at the easternmost point BM 1026 is -0.2 mm. No appreciable change was observed for the last 14 years. This fact supports a working hypothesis of crustal uplift after deglaciation. It is inferred from geomorphological data that the crust around Syowa Station continues to uplift at the rate of 2-6 mm/y for the several thousand years. Oceanic tide data at Syowa Station shows that the sea level is going down at the rate of 4.5 mm/y. The occurrence of the local earthquakes caused by stress accumulation due to crustal uplift after deglaciation indicates that the crustal uplift is not a linear phenomena but an intermittent one, associated with block movement. The observations from repeat leveling measurements suggest no significant changes, which further supports the idea that the crustal uplift is a block movement.View full abstractDownload PDF (514K)
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