-ll- 
types in sea ice. The waves were generated with explosives, blasting caps 
and falling weights. The waves were recorded with an HTL = 7000-8 
seismograph system. Detectors were 2 cps anc 1 eps eeophones. Many records 
were made for the study of wave propagation in sea ice. The results of 
these studies were reported in the Journal of Geophysical Research, October 
1960. Thickness and density measurements were also made and reported in 
the same paper. 
Some studies of ice tremors were also made. The general level 
of ice tremors did not seem to be hich at Alpha, althouch the seismograph 
was turnec on daily for brief periods. The author saw them only: briefly in 
September, 1957 and weak ones in the spring of 1958. Apparently they were 
observed and heamiby van der Hoeven at intervals during the winter. The 
tremors recorded in September, 1957, traveled chiefly with the shear velocity 
and were predominantly impulsive, elthough some flexural waves were seene 
Tremors were recorded on the sea ice at T-3, Colby Bay in 1960 anc the 
percentare of flexural waves seemed higher and the source more localized. 
Several recordings were made on magnetic tape and full analysis of these 
is yet to be completed. Ice tremors are the largest source of background 
noise in the Arctic ocean and deserve cereful study. Recordings are being 
made at T-3 this winter to increase our knowledge of this phenomenon. 
III. PACK ICE MOVEMENT 
Data were collected at Drifting Stations Alpha and Charlie for 
the continuing study, by Mrs. Irene Uotell, of the drift of ice in the 
Arctic Ocean. Navigation and wind observations are the most important data 
for these studies. Celestial navigation et Alpha was cone by Lamont scientists 
throughout its occupation. At Charlie, navigation was done by University of 
Washington scientists during the entire drift an? simultaneously by Lamont 
scientists during the winter. Results of these observations are included in 
