Rit (Vísindafélag Íslendinga) - 01.06.1971, Blaðsíða 10

10
GUÐMUNDUR PÁLMASON
P-wave velocities are presumably an indicator of the relative poro-
sity of the rock which is of prime importance for the hydrothermal
circulation systems. The present work also indicates that there may
exist a close relationship between some of the seismic boundaries and
the past or present subsurface temperature field. When the seismic
data are combined with gravity data, the average densities of rocks
at various depths can also be obtained.
The present work aims, firstly, at giving as detailed a description
of the seismic structure of the crust in Iceland as presently available
data allow; secondly, to interpret this structure in geological terms
using other geophysical and geological data; and thirdly, to discuss
in broad terms the implications of the results for prevailing theories
of the formation of the mid-ocean ridges.
Some of the data which are presented here have been published
elsewhere (Pálmason, 1963, 1965, 1967a), but they are discussed
from a somewhat different point of view and in some cases reinter-
preted in the light of new data. Most of the material, however, has
not been published elsewhere.
No attempt has been made to review the literature on Icelandic
geology except insofar as it relates directly to the present work. For
additional information thereader is referred to ThÓrarinsson (1965),
Walker (1964, 1966), Björnsson (1967) and Sigvaldason (1969),
where other references may be found. The reader is also referred to
the revised geological map of Iceland. Five sheets covering southern,
western and central Iceland have been published at the present time
(Kjartansson, 1960, 1962, 1965, 1968, 1969).
2. SCOPE AND ORGANIZATION OF FIELD WORK
In the first 2—3 years of the field work the emphasis was on rela-
tively short profiles, 25-40 km, to study the upper crust, the “lava
layer” as termed by Báth (1960). These profiles were distributed all
over Iceland, more densely in the coastal areas than in the interior.
Some 30 profiles were measured in northern and eastern Iceland
(Pálmason, 1963), and some 30 profiles in southern and westem
Iceland. These profiles were sufficiently long to give information
on depth to layer 3 (Báth’s layer 2). The location of individual pro-
files was usually decided by considerations of accessibility and shot
point availability. The profiles were usually unreversed and the shots
fired in lakes, rivers, or in the sea. Only one set of refraction instru-