Fróðskaparrit - 01.01.1976, Page 18

26 Seismic Refraction Measurements around the Faeroe Islands
Conclusion.
The basalt lavas of the Faeroe Islands have been found to
be underlain by a probably thick layer of a velocity about
5.9 km/s. If this layer is covered exclusively basalt lavas
of a mean velocity of 4.9 km/s then the thickness of the
lavas varies between 2.2 and 4.8 km (corresponding to time
terms between 0.25 and 0.54 s) with a mean value about 3.5
km. No correlation has been found between these time terms
and the gravity anomalies on the islands.
On the northwestern shelf the velocities below the basalt
lavas may be slightly higher, perhaps 6.2 km/s, but no effect
has been found to be caused by the very deep and narrow
gravity minimum of about 40 mgal. The time terms of the 6
km/s refractor are rather irregular in the region, but the
increase of 0.3 s found at A3 can hardly be compared with
the gravity minimum which requires a structure with a thick-
ness of more than 5 km and a density contrast of at least
0.2 g cm“3 (Fleischer et al. 1974 and Casten 1974). The simp-
lest explanation seems to be a granite batholith (Schrøder
1971).
The data from line B indicates a (unreversed) velocity
of perhaps 5.3 km/s, Moho seems to be the only other re-
fractor observed in the region.
The velocities of 5.9 to 6.2 km/s and 5.3 km/s point towards
a continental structure, just as the gravity data (Bott & Watts
1970). The Moho time terms of line B are around 3.5 s and
give a depth to Moho of 24 km, if the velocity above Moho
is taken as 5.3 km/s (a very low crustal velocity) and below
Moho as 8.2 km/s. On the British side of the Faeroe-Shetland
channel the depth to Moho has been found to be close to 25 km
(Smith & Bott 1975), but the structure of the channel itself has
not been revealed yet.
According to observations at the array station UKAEA in
the Shetlands (fig. 8) the shots in the gravity low on line B
may have Moho time terms slightly higher than the shots