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Volume 46 (2000)
- Issue 4 Pages 239-
- Issue 3 Pages 177-
- Issue 2 Pages 89-
- Issue 1 Pages 1-
Volume 46, Issue 1
Displaying 1-6 of 6 articles from this issue
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Yuki Kuroishi2000 Volume 46 Issue 1 Pages 1-20
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSThe paper outlines the fundamentals of the geoid determination theory and clarifies the importance of understanding the permanent tidal systems and the absolute scaling of the geoid. Concrete formulas for a local geoid recovery in a 'remove-restore' manner with a global geopotential model are described and applied to result in gravimetric geoid models for Japan. A first model, JGEOID93, and its improved one, JGEOID98 are introduced and evaluated in rela tion to ship gravity data. Because of the geological setting of the Japanese islands at a trench and island-arc region, ship data are essential to determine the geoid even on land. The evaluation makes it clear that an appropriate method needs to be developed for fixing ship gravity data at long wavelengths. Combined use of altimeter and ship gravity data is tested and confirmed in its effectiveness, but the necessity is identified to design a non-isotropic weighting/filtering based on the data. Upcoming satellite gravity missions are discussed how we can carry out a better geoid modeling from the results of such missions.View full abstractDownload PDF (6039K) -
Burkhard Schaffrin2000 Volume 46 Issue 1 Pages 21-30
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSIt has long been argued that Minimum Mean Square Error Estimation, although theoreti cally superior to the least-squares adjustment, is impractical in the absence of any prior information on the unknown parameters. The Empirical BLE therefore applies another estimate from the same dataset, e.g. the BLUUE (Best Linear Uniformly Unbiased Estimate) or the ridgeestimate, in order to overcome this problem. Here, we introduce the repro-BLE (Best Linear Estimate with the reproducing property) which - if it exists - belongs to the same class of (nonlinear) estimates, but with the provision that the vector used to form the empirical meansquare error risk coincides with the eventual estimate, thus fulfilling the "reproducing property". A few elementary examples for the case of direct observations clarify this approach and may help to understand the behavior of repro-BLE in comparison to the more commonly used Empirical BLE, or to the BLUUE that is generated by a (weighted) least-squares adjustment. The more general Gauss-Markov model will be treated in a second part.View full abstractDownload PDF (750K) -
Minoru Tanaka2000 Volume 46 Issue 1 Pages 31-42
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSFrom the analyses of crustal strains in Kyushu district, it was cleared that the upheaval area is in good agreement with the zone of the increasing dilatation. This upheaval area is accompanied with the development of zones of relatively rather larger rates of maximum shear strains that occurred around the area as a result of the regional tectonic field. On the other hand, the occurrences of the earthquake zones associated with active faults are observed on both sides of the dilatation area and are dependent on the tectonic compressional direction on the earth's surface. In place where there is increasing geoidal undulation, which apparently corresponds to the growing dilatation zone, no seismic area is likely to be formed. From these results, intraplate earthquakes are expected to occur around the zone of in creasing geoidal undulation so as to stabilize the geopotential in the area and to regulate fur ther crustal upheaval. This is clearly manifested in Kyushu district by the existence of major geological structure such as active faults and fracture zones found around the dilatation zone.View full abstractDownload PDF (1889K) -
Taku Ozawa, Koichiro Doi, Kazua Shibuya2000 Volume 46 Issue 1 Pages 43-52
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSWe applied the three-pass Synthetic Aperture Radar (SAR) interferometry method to the Soya Coast area, East Antarctica, and detected the ice flow field. Although the obtained ice flow from SAR interferometry was constrained to the line-of-sight direction component, the three dimensional ice flow vectors could be estimated by assuming the ice flow direction. Inthe fast ice flow area, the streamlines often appear as bright (white) curves in the intensity image, and the direction of the curve is almost consistent with the ice flow direction. The streamline direction of a certain point on the Langhovde Glacier (point A) can be identified as N86°W, and the ice flow value using this direction and the direction of line-of-sight component of ice flow can be estimated as 86.2 m/yr. If we assume that the ice flow direction is approxi mated by the maximum gradient direction of the ice sheet surface, the ice flow direction of point A results in N64°W, which differs by 22°from the ice flow direction estimated from the streamline. We calculated the maximum shear strain and the dilatation fields from the estimated ice flow vector field. The larger maximum shear strain values around the marginal areas of the ice stream indicate stronger deformation by stress at the transition zone from the slow ice sheet area to the fast ice stream area. On the other hand, there appeared a characteristic con traction area around 600 m height, and we compared its location with the features in the aeromagnetic anomaly maps obtained over the same region. There is a saddle area in the magnetic anomaly map with relative highs near the contraction area. This area may correspond to the topographic rise of the subglacial bedrock relief.View full abstractDownload PDF (9413K) -
Yoichi Fukuda2000 Volume 46 Issue 1 Pages 53-67
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSThis paper reviews satellite altimetry mainly from a geodetic and oceanographic point of view; discusses the relationship between satellite altimetry and gravity missions; besides it gives a preview of the gravity missions and their meaning in the study of the Earth's sciences. Satellite altimetry is a technique for measuring sea surface heights from a satellite orbit using a microwave radar altimeter. This technique has brought about a revolution in the study of marine gravity fields, and then in the oceanographic studies. With the sea surface being a good approximation of the geoid, sea surface heights measured by satellite altimeter are con sidered to be approximate geoid heights. On the other hand, there exist small differences between sea surface and geoid heights. The differences are referred to as sea surface dynamic heights which are caused by the ocean currents. Therefore absolute current flux could be de tected by satellite altimetry, if precise geoid is determined independently from satellite altimeter data, This is the main reason why a precise oceanic geoid has been desired for a longperiod of time by oceanographers. All the satellite gravity missions which were planed late 1980's and early 1990's aimed at the improvement of the accuracy of static gravity fields. Compared with these missions, GRACE has a rather different concept. Very accurate measurements by GRACE will be expected to reveal not only precise static gravity fields, but also the temporal variations of the gravity fields. GRACE aims, for the first time in history, to ob serve various mass movements which occur in, on and above the Earth's surface as gravity changes. There is no doubt coming satellite gravity missions will bring about revolution in the studies of the Earth's sciences.View full abstractDownload PDF (2488K) -
Hwa-Chu Sheu, Li-Fang Yu, Hiroshi Sato2000 Volume 46 Issue 1 Pages 69-82
Published: March 25, 2000
Released on J-STAGE: September 07, 2010
JOURNAL FREE ACCESSFaults that generated the1935 Hsinchung-Taitung earthquake and the 1999 Taiwan earthquake are discussed from the viewpoint of crustal movement. Main fault of the 1935 quake is of westward dipping reverse-type and that of the 1999 quake is an east dipping reverse fault, though the both faults are closely located and are aligned nearly straight from north to south. The topographical arrangement in the focal area is, from east to west, Foothill of Central Range, Taichung basin, Platform and Coastal Plain. The 1999 fault is located at the western side of the Foothill and that of 1935 is at the eastern side of the platform. The both faults have symmetrical location with respect to the Taichung basin. Seismic moment (Ma) of 1935 earthquake is obtained as 0.3.1020 N? m from the fault model using geodetic data, and that of 1999 quake is estimated as 4.3.1020 N? m from the GPS and leveling data. A static fault model by the leveling data of 1999 Taiwan quake is presented . Horizontal movements calculated from the model are nearly consistent with those observed by GPS. The tectonic background of the both earthquakes is discussed from the viewpoints of geology, seismology and crustal movement. Tectonics of Taiwan is characterized by the collision between Philippine Sea plate and Eurasian plate at eastern Taiwan, where many points are still remained unsolved as further discussion.View full abstractDownload PDF (6132K)
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