Jökull - 01.06.2000, Side 45

Comparison of tomographic crustal models with gravity data
Figure 8. Bouguer anomaly fields upward continued to a plane 1 km a.s.l. and adjusted to a mean of 0 mGal.
The contour intervals are 0.5 mGal. (a) The observed field, and (b) the simulated field. - Mœlt (a) og reiknað
(b) Bouguer þyngdarsvið á Kröflusvœði á plani einum kílómetra ofan sjávarmáls.
When compared with the LET model, this patt-
ern of density variations shows some similarity, within
the resolution of the LET, to the velocity anomalies
determined at sea level (Figure 4a). The LET determ-
ined velocities at 2 km intervals laterally (3 km along
the eastern edge of the study area) and thus spatial
discrepancies of up to 1 km between the centres of
velocity anomalies (Figure 4a) and density anomalies
(Figure 10) may be attributed to coarse resolution in
the LET model. Velocities up to ~ 1 km/s higher than
the average are imaged around the caldera and bene-
ath Leirhnjúkur, in the neighbourhood of areas wh-
ere high densities are required by the gravity field.
The gradient of the velocity-density relationship used
(Equation 1) is 230 kg/m3 per km/s and thus a velocity
anomaly of 1 km/s would correspond to a density
anomaly of 230 kg/m3, in approximate agreement
with the gravity inversion results.
ln(E)
11n
DD°
z 0.7 km
□ cut off
1.5km
□
b □ □ D
Wavenumber
6 (Km'1)
Figure 9. Graph of the natural logarithm of the power
spectrum vs. wave number for the upward continu-
ed, observed gravity field. - Línurit sem sýnir náttúr-
lega logrann af aflrófi fyrir mismunandi bylgjulengdir
þyngdarsviðsins.
JÖKULL No. 48 43