Jökull - 01.12.1970, Blaðsíða 43

Fig. 2. Cross-section of Tungnárjökull along the line N2—NKP as calculated from the gravity
survey in 1967 and seismic survey in 1955.
Mynd 2. Þversnið af Tungndrjökli eftir línunni N2—NKP reiknað út frd þyngdanntelingunum
1967 og jarðsveiflumœlingunum 1955.
used out to the distance of 16 km (Nettleton,
1940; Sandberg, 1958). The corrections were
small (< 0.5 mgal) except in SNR (> 2.0 mgal).
Terrain corrections at other stations were ob-
tained by linear interpolation.
We obtain the two-layer Bouguer anomaly in
all reference stations except K10 and K18. As
an estimate for the height of the underlying
bedrock we use results from J. P. Martin’s seis-
mic survey. We take account of the SW—NA
tendency in all landscape features in this esti-
mation. Neither N2 nor SNR are situated on
ice so here the two-layer anomaly reduces to
a one- (bedrock) layer anomaly.
An estimate for the two-layer Bouguer ano-
maly along both survey lines is shown on top
of Figs. 2 and 3. We base it on the values
obtained at the reference stations but assume
it to be linear between N2 and NKP and SNR
and NKP resp. rather than insisting on full
agreement with each of these values (indicated
with crosses in the figures). From the difference
between the one-layer ancl tvo-layer Bouguer
anomaly we calculate the ice-thickness as ex-
plained in preceeding section. ei = 0.9 g/cm3
and two values are considered for 02 2.0 ancl
2.5 g/cm3. Results in both cases are presented
at bottom of Figs. 2 and 3. The calculations
were carried out on the IBM 1620 computer
of the University of Iceland.
DISCUSSION OF RESULTS
The main points where irregularities or
ridges are observed on the bedrock surface
under the lines of gravity survey are marked
JÖKULL 20. ÁR 41