Irreducible Decomposition of the U_n₊m-module of (r,s)-forms on the Complex Grassmann Manifold Gn₊m,n

Article信州大学理学部紀要 22(1): 13-26(1987)departmental bulletin pape

Upper crustal structure of the Prince Olav Coast, East Antarctica

The P-wave velocity structure of a part of the Prince Olav Coast, East Antarctica was revealed by a seismic refraction experiment conducted by the 21st Japanese Antarctic Research Expedition in July 1980. Ten seismic stations were set along a line with a length of about 10 km at intervals of about 1 km. The station consists of a seismometer and a direct analogue data-recorder with an electric panel-heater in an insulated box. The observed travel times of the first and later arrivals from two explosions at both ends of the line were analyzed. The P-wave velocity of the basement complex is 6.02 km/s which is a typical value in East Antarctica. This basement complex is covered by the ice sheet with the thickness of about 700-1000 m. No layer with a velocity less than 6 km/s is detected between the ice sheet and the basement complex

Nature of noises on ice sheet in East Antarctica

Two types of noise recorded in seismic explosion experiments around Syowa Station in Antarctica are discussed. One is wind-induced noise which is detected directly by a seismometer. This type of noise increases with a wind velocity, and when the wind velocity is over 15 m/s, seismic observations are not in success. With the object of noise reduction, seismometers buried in a hole at depths of 3, 5 and 10 m were examined, but the noise existed at 10 m. Seismometers should be buried deeper than 10 m. Another is electrostatic noise which frequently deranges a clock signal or destroys an electric circuit in the worst case. This noise is caused by drifting electrified snow, not by a seismometer itself. It was excited on a signal cable stretched on the snow surface from the seismometer to a recorder. To reduce this noise, the cable should be as short as possible and be laid in parallel with the direction of wind

Amplitudes of seismic waves on ice sheet in East Antarctica

In 1979-81, ten shots were fired in drill holes at the Prince Olav Coast and the Mizuho Plateau, Antarctica, for explosion seismic experiments by JARE-20, -21 and -22. The yield ranged from 10 to 1400kg. An empirical relationship between yield and maximum amplitude of seismic wave was derived for shots in drill holes in ice sheet. This will help to design an adequate charge size for explosion seismic experiments in Antarctica. The maximum amplitudes obtained are compared with those generated from explosion in sea water in Antarctica and in solid rock in Japan. For yields smaller than 500 kg, the logarithm plots of the amplitudes are in a linear relation with the logarithm of yields, and the amplitudes are about 1/5 to 1/8 of those generated in solid rock. For the yields larger than 500 kg, the wave amplitudes in the ice sheet become larger than those estimated from the above relationship. The amplitude of the biggest shot of 1.4t detonated in the ice sheet is nearly the same as that in solid rock in Japan. This is because small shots were fired in shallow drill holes where the ice is very porous, its density is only about 500 kg/m^3. The biggest shot was fired at a depth of 140 m in the ice with a density of 800 kg/m^3 or greater. The maximum amplitudes of seismic waves generated from a 1-t explosion in sea water are about 8 to 10 times larger than those from equivalent explosions in the ice sheet. The relation is similar to the results obtained for shots in sea water and solid rock in and around Japan