Fróðskaparrit - 01.01.1977, Page 90

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A marine geophysical project
lavas a digital registration would have been a valuable aid and
a digital registration is planned for the continuation of the
measurements to the sea south and south west of the Faeroes
(summer 1977).
The purpose of the magnetic measurements is primarily to get
a mapping of the structures and extension of the rather mag-
netic basalts. The basis of such an analysis must be a know-
ledge of the magnetic properties of the rocks. As a random
choice a number of dredged erratics have been measured in the
laboratory and the mean value of the susceptibility was found
to be around 0.002 (cgs-units) and the Q-ratio:;') scattered from
less than 1 to more than 10 with a mean value of about 4;
these results are in agreement with previous results (Hansen et.
al. 1973 and Løvlie et al. 1975).
The interpretation will be published elsewhere but the main
'features of the measured magnetic field are shown by fig. 2
and 3. The magnetic field is highly irregular close to the islands
but generally with larger amplitudes to the west than to the
east. At some distance east of the islands the field becomes
smooth and with a very small variation until the deep Faeroe-
Shetland channel is approached; the channel is connected with
a smooth anomaly of a few hundred gamma. The western
boundary of the smooth field east of the Faeroes seems to
follow the deepest part of the depression between the islands
and the banks to the east of the Faeroes (Nólsoyar banki and
Sandoyar banki); this may be the eastern boundary of the
Faeroese lavas.
The channel between the Faeroe Islands and the Faeroe Bank
in the south west is also connected with a rather smooth field
which indicates that the magnetic basement is at a considerable
depth in the channel.
During the campaign the magnetic field was measured con-
tinuously at Royndarstøðin in Hoyvík near Tórshavn and this
co-operation is gratefully acknowledged.
!í) The Q-ratio is the ratio of the remanent (permanent) magnetization
divided by the induced magnetization in the normal field of the Earth
(here 50 000 gamma = 0.5 gauss = 50 000 nT).