Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 76

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the delay times recorded at three seismologic stations situated in
south-westem, southem and north-eastem Iceland and assuming
the crustal structure beneath the island to be uniform, Francis ob-
tained lower (up to 7 km/sec) velocities in the upper mantle. He
also estimated the thickness of the low velocity zone to extend down
to a depth of approximately 250 km.
The gravity curves show minimum Bouguer anomalies to be -30
mgal in central Iceland and the gravity field to increase to values
of +40 to +60 mgal towards the coast. The contours of the Bouguer
anomaly isolines simulate those of the coasts (10). The recent sur-
veys have revealed the gravity field to be locally complicated,
though the general pattem remained undistorted (Pálmason, 1973,
personnel communication).
The estimation of the anomalous gravity fields together with the
seismological data obtained by Francis confirms their possible cor-
relation (9).
For the areas of the Iceland-Faeroe Ridge and the ocean between
the Faeroe and Shetland Islands and northern Scotland the gravity
field is composite and variable (11). A relative maximum up to 110
mgal has been recorded on the Ridge, while a relative minimum
(—20, +30 mgal) over the Faeroe-Shetland channel as well as
near the Iceland coast and the Faroes. These are the main data
obtained so far for the structure beneath the regions under investi-
gation.
DSS Observations in NASP
In 1972 a seismological group of the Soviet Expedition in Iceland
and a team from the research vessel “Mikhail Lomonosov” partici-
pated in the recordings of the seismic waves to NASP1. The project
undertaken by Durham University (12) involved detailed investi-
1. NASP explosions were recorcled on land by S. M. Zverey, A. N. Fursov, G. N.
Akimov, and offshore by V. M. Shablitsky, V. V. Knyazev, 0. A. Kiselev (In-
stitute of Physics of the Earth, Ac. of Sc., USSR, Moscow) and E. V. Zhit-
kovskaya, V. A. Kapianidze (Acoustic Inst., Ac. of Sc., Moscow). In interpre-
tation of the data collected the authors were assisted by G. P. Vastchinnikova,
E. N. Zaitseva, N. K. Kapustyan, I. S. Lysova, N. I. Pavlenkova, Y. V. Tulina,
G. A. Yaroshevskaya (Inst. of Physics of the Earth).