南極・昭和基地の水準測量とその解釈

抄録

A 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.