| Research Abstract |
GPS interferometry is applied to investigate crustal deformation at plate boundaries. The present study aimed at initial occupations of sites and fundamental research for examining the best approach to apply the technique. In 1987, reconnaissance surveys were made and the South Kanto area and the Hokuriku area were selected as study area. Hokuriku area was put special attention from the standpoint of tectonic significance, where Itoigawa-Shizuoka tectonic line, Tateyama active volcanoes and Atotsugawa active fault system are located. The initial occpation conducted in 1988 employed WM101 single frequency receivers. Baseline analysis at this year showed short-term repeatability in the order of pert per million. In order to improve the repeatability by reduction of errors due to ionospheric effects, WM102 dual frequency receivers were used in 1989. Stations at Toyama, Kanazawa, Kamitakara, Tateyama, Nobeyama in addition to Uji were established. Coordinates of these stations were precisely estimated based on the colocation at the Nobeyama VLBI site. Observation in 1989 showed much better repeatability in the order of 0.1ppm. Extensive analyzes of these years have been executed and significant site displacements were found. Rhombus that consisted from Toyama, Kanazawa, Tateyama and Kamitakara showed areal extension. On the other hand, large triangle which is made up from Toyama, Nobeyama and Yahiko showed N-S Extension and E-W compression. We suggest that a few more years of repetition will clarify the crustal deformation in the area. Thus, generally speaking, the present way of GPS measurements and processing would result in enough accuracy in detencing plate motions of the order of a few cm's a year by within 5 years of repeated GPS measurements.
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