Rit (Vísindafélag Íslendinga) - 01.06.1967, Qupperneq 76

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Two structure sections are shown here in Figs. 3 and 4 to
illustrate the general features of the results. The first one,
a section across the northern Iceland in an east-west direc-
tion, shows the characteristic layering (Pálmason, 1963). The
second section, in southern Iceland is based on unpublished
results, and is of a prelhninary nature. The layering is more
irregular here than in northern Iceland. Layer 2 seems to be
absent in the western branch of the neovolcanic zone. Fur-
thermore there appear to be variations in the velocity of
layer 3 in a horizontal direction along this section.
As layer 3 is of particular interest, Figs. 5 and 6 have been
drawn to show the P-wave velocity values ohserved for this
layer as well as its depth below sea level. It should he kept
in mind that most of the profiles are unreversed and errors
due to this may be present on any single profile. In many
areas, however, there is a sufficient number of profiles to
enable fairly reliable deductions to be made as to velocities
and depths.
The velocity values are usually in the range 6.0 to 6.7
km/sec. There appear to be some systematic variations in
velocities from one area to another. This is particularly clear
in southwest Iceland. On the westem side of a line which
follows the westem boundary of the neovolcanic zone, velo-
cities are high, averaging about 6.5 km/sec, but on the east-
ern side they are lower, averaging about 6.2 km/sec. Similar
trends can be seen in other parts of Iceland, but further stu-
dies are required, in particular to greater depth, to elucidate
further the relation between these two apparent subgroups
(cf. also Fig. 2).
Fig. 6 shows that the maximum depth to layer 3, between
4 and 5 km, is found along the eastern branch of the neo-
volcanic zone, and also in an area in central northern Ice-
land. The shallowest depth is between 1 and 2 km in several
areas. The difference in structure between the two branches
of the neovolcanic zone is worth pointing out.