=-6= 
with hydrophones are absent. 
Seismic refraction work was continued at ice island, T=3, during 
March, April and May, 1960. Arrangements were made with Max Brewer at Arctic 
Research Lab, Point Barrow, for the use of his Cessna airplanes in order to 
reach greater distances. Landings were made on pack ice and explosions 
detonated which were received at T-3 on a geophone array. The work proved 
the feasibility of the method anc some good records were obtained. Traverses 
were also made alcng the edge of the island and shots made out to about 
8 km. The original intention was to study crustal structure in the Arctic 
Ocean basin. However, the station drifted over the continental shelf during 
March and all subsequent work was done in relatively shallow water. 
Refracted arrivals were not clear and this may be due to thick layering 
or to confused and disrupted layers. The arrivals were largely due to 
normal mode propagation in the ice-water-sediment system. These dispersed 
arrivals are to be interpreted by comparison with theoretical models 
calculated on an electronic computer. This data reduction and interpretation 
is still in progresse At present it appears that an excellent fit of theory 
to experiment can be made which results in an interpretation of the 
sedimentary layers of the continental shelf off Point Barrow. 
A long-period vertical spregnether seismograph was operated at 
Station Charlie. The background of ice wave motion in the 30 to 50 second 
period range was high. The only earthquake which was detected was that of 
Wyoming-Montana, August, 1960. The background motion shows no clear correl- 
ation with local winds and pressure. Power spectrum analyses have been made 
of some of the records. 
