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vessel “Miranda” and on the Soviet ship “Mikhail Lomonosov” and
on the islands by scientists from Great Britain, Denmark, Iceland,
USSR and USA. The offshore work was supervised by Dr. J. Sunder-
land, the overall coordination of NASP exercised hy Prof. M. H. P.
Bott (hoth from Durham University, UK).
The Soviet expedition provided 6 stations in northem Iceland
spaced on the continuation of line A of NASP and 5 offshore obser-
vation points. Single type equipment such as autonomous seismic
stations with continuous magnetic tape recording were employed
(13). On land as well as at the sea bottom the signals were recorded
hy 3-component detectors assisted at sea by the hydrophones on the
floating stations.
Along with the shots fired on NASP line A the land stations
recorded explosions fired by the Iceland geophysicists in the Huna-
floi Bay at the north-westem end of the array of observation sta-
tions (see Fig. 1). Explosion N 4 was registered at stations R5, R4,
R3 and AKU and was used in the interpretation in spite of a doubt-
ful shot time.
The conditions for observations of the seismic waves in Iceland
and the adjacent water tumed out to be favourable. The noise level
in the frequency band of 3-12 cps at line A is one order less than
those at many places of the continents as well as the oceans. This
provided a successful record of the seismic arrivals from charges
less than 200 kg in weight over a distance of 560 km at the land
stations and more than 250 km offshore. Good-quahty records from
the charges of 10 and 20 kg in weight were obtained at distances
approx. 150 km, which agrees well with the records of the seismic
waves in Iceland reported by Pálmason (1).
Having completed the observations, the investigators exchanged
the first seismic wave travel time tables and in part the record
copies. It made it possible for every participant to process the
data independently. The interpretation problems were discussed at
the time of mutual visits of the scientists of Institute of Physics of
the Earth, Academy of Sciences USSR, to Durham and the mem-
bers of the Durham University to Moscow, and during the stay of
Dr. G. Pálmason in Moscow in 1973.
The data presented below are based on the analysis of the records
from the Soviet stations and the copies from the Iceland station Mx.