Antarctic Record (Sep 1983)
Field operation of explosion seismic experiment in Antarctica (second paper)
Seismic refraction experiments were carried out to investigate the crustal structure in Antarctica by the wintering party of the 21st Japanese Antarctic Research Expedition. Five experiments were made from May 1980 to January 1981 in the vicinity of Syowa Station and in Mizuho Plateau, East Antarctica. The outline of the experiments is reported with respect to the field operation and the preliminary results. In May and June 1980,the shallow structure of an ice-free area in the vicinity of Syowa Station, Ongul Islands, was revealed by small-scale experiments. The P-wave velocity in this area is 6.0-6.3km/s. In July a preliminary experiment was conducted in the ice field on the Soya Coast along a line of about 10km long, in which many tests were performed for ice drilling, blasting of dynamite and installation of recording system at air temperature as low as -30℃. Shallow structure of this area was also obtained in the experiment. The P-wave velocity under the ice sheet is 6.0-6.2km/s which is nearly the same as that of the ice-free area. After the success of the experiments two large experiments were conducted along a line of about 300km long between Syowa and Mizuho Stations from October 1980 to January 1981. Explosions of 1400 and 1000kg in charge amount were fired in an ice hole of 143m deep at one end of the line near Mizuho Station and 100m deep at the middle of the line, respectively. In addition to the shots a large explosion of 3000kg in charge amount was detonated at a depth of 160m in Lutzow-Holm Bay off the Soya Coast, the other end of the line. The waves generated by the explosions were recorded successfully at 27 observation stations set up along the line. The former experiment was carried out by ten to fifteen persons for a period of forty days and the latter for a period of fifteen days. The apparent velocity of P-wave in the upper crust varies from 6.0 to 6.4km/s, suggesting gradual increase with depth in the layer. The apparent velocity of 7.9km/s for P_n wave was observed as first arrivals and that of 6.9km/s for P^* as later arrivals.