Rit (Vísindafélag Íslendinga) - 01.06.1971, Side 67

CRUSTAL STRUCTURE OF ICELAND
67
anomaly occurs in a southward direction near the center of the valley,
perhaps near Flugumýri.
It is perhaps of some significance that the hot springs which are
plentiful in the Skagafjördur valley, occur mainly south of Varma-
hlíd which is on the west side of the valley opposite Flugumýri. The
hottest springs are at Varmahlíd, about 100°C. Farther to the south
many hot springs are found aligned more or less along the valley.
North of Varmahlíd the hot springs are much less common. As was
suggested for Hrútafjördur, it is also possihle here that the hot-water
is directed towards the surface from a southward direction by lavas
dipping to the south.
The structural anomahes in Skagafjördur are reflected in the pro-
file Vesturhóp—Skagafjördur (LIO). At Varmahlíd at a distance of
52.4 km from the shot point the delay time is the same as along most
of the profile up to that distance. At the next station which is ahout
10 km farther south along the Skagafjördur valley the delay time is
increased by about 0.16 sec. This must be due mainly to the north-
south structural change which begins just south of Varmahlíd. Se-
veral seismometer stations were set up at larger distances between
Skagafjördur and Eyjafjördur, but the arrivals were usually weak.
This may in part be due to the structural changes in Skagafjördur.
In Eyjafjördur the two profiles F and G of Tryggvason and Báth
(1961) give information on the delay time of the P3-wave. They are
measured in opposite directions, profile F northward from a shot
point in lake Hólavatn, and profile G southward from a shot point in
the sea about 2 km north of Dalvík.
Profile G shows much the same behaviour as the Blönduhlíd pro-
file in Skagafjördur, which is oriented in the same way. The delay
time of the P3-wave increases on both profiles in a southward direc-
tion indicating increased depth to layer 3. Absolute delay times and
depth to layer 3 are somewhat smaller on profile G than on the
Blönduhlíd profile. Depth to layer 3 near the shot point of profile G
is 2.6—2.8 km depending on the relative thicknesses of layers 1 and 2.
The southernmost seismometer station on this profile was in Hörgár-
dalur at a distance of about 35.4 km. The delay time is here larger by
about 0.25 sec, indicating a depth of about 4.6-4.8 km to layer 3.
Profile F indicates a delay time of about 0.50 sec for the P3-wave
near the shot point. Layer 1 is a surface layer along most of this pro-
file with an average thickness of 0.5 km (Pálmason, 1963). It is
underlain by layer 2 with an average velocity of 5.0 km/sec. The