Study of Geoid Undulation in Southwestern Japan

1.为了准确确定日本西南部的大地水准面起伏，收集了重力测量、水准测量和潮汐观测数据以及卫星测高数据。用WM102型GPS接收器在日本西南部的57个点进行了GPS测量。GPS测量高度的平均重复性为5.5 cm。通过比较GPS测得的大地水准面高差与水准测量获得的大地水准面高差，确定了这些点处的大地水准面起伏差。在鸟取、别普、基伊和四国地区，使用LaCoste和Romberg重力仪进行了精确的重力测量。根据上述(1-3)资料，绘制了日本西南部大地水准面起伏差等值线图。本研究确定的大地水准面差异与之前的大地水准面基本一致，如ORI-89大地水准面，但检测到了几十厘米量级的系统差异。将GPS/水准大地水准面起伏差与迄今由P波走时分析得到的三维地震速度各向异性进行了比较。

1. In order to determine the geoid undulation precisely in the southwestern part of Japan, data obtained from gravity measurements, levelling surveys and tidal observations as well as satellite altimetry data have been collected.2. GPS measurements at 57 points in the southwestern part of Japan have been carried out with WM102 GPS receivers. Average repeatability of heights measured by GPS was 5.5 cm. Geoid undulation differences at these points have been determined by comparing ellipsoidal height differences measured by GPS with orthometric height ones so far obtained from levelling surveys.3. In Tottori, Beppu, Kii and Shikoku regions, precise gravity measurements were performed with LaCoste & Romberg gravimeters.4. Based on data mentioned above (1 - 3), a contour map of geoid undulation differences in the southwestern part of Japan was obtained. The geoid differences determined by the present study were approximately consistent with the proceeding geoids, such as the ORI-89 geoid, but systematic discrepancies of the order of a few ten centimeters were detected.5. GPS/levelling geoid undulation differences were compared with three-dimensional seismic velocity anisotropy so far obtained from P-wave travel-time analyses.