Fróðskaparrit - 01.01.1976, Blaðsíða 4

12 Seismic Refraction Measurements around the Faeroe Islands
and the dip of the lavas is everywhere small (Noe-Nygaard
1962, 1974, Rasmussen and Noe-Nygaard 1969). The lava
flows have been dated to be between 50 and 60 Ma old (1 Ma
=r 106 years) (Tarling and Gale 1968). The topography of the
islands is rather rough, especially of the north-eastern islands,
and in the northern parts heights of nearly 900 m are reached.
The basalt layers mentioned cannot be studied in any detail
by using NASP-data, because nearly all ranges are too big to
give first arrivals in the top layer. However, these layers were
studied by Pálmason (1965), who found the following struc-
ture:
V V
P s
upper series 3.9 km/s 2.2 km/s
middle series and lower series 4.9 km/s 2.7 km/s
basement 6.4 km/s 3.4 km/s
The three series are basalt lavas and crop out on the islands.
The depth of the unknown basement was found to be between
2.5 km and 4.5 km beneath Streymoy. From these results
Pálmason inferred that the structure was of the Icelandic type
(Bath 1960, Pálmason 1971, Pálmason and Seamundsson 1974),
but the lines were too short to give reliable results for the base-
ment (Pálmason 1965).
In 1970 further seismic work was done on the islands (Casten
1973); line 1 (fig. 2) was fired and observed by a number of
stations on the islands. Unfortunately, the telemetric hydro-
phone buoys failed so the shots were observed on land only
(Casten 1974). However, the apparent velocities seem to con-
firm Pálmason’s previous results except that the apparent velo-
city of the basement was found to be lower, namely 5.9 km/s
(Casten 1973).
Besides the seismic work the gravitational field has been
measured and a detailed map of Bouguer anomalies with topo-
graphic corrections has been published by Saxov (1969). The
gravitational field is according to these maps rather uniform