Fróðskaparrit - 01.01.1968, Page 72

80
A Note on some Geo-Electrical Measurements
fjord and the steep rock walls curving south of Tjørnuvík
indicate that the topographical form has been glaciaily mo-
delled as a glacial cirque. In tshe most southern part of chis
glacial cirque sediment depositions have formed a small plat-
form, the surface of which lies 5 to 10 m above present sea-
ievel.
Because of previous archaeological findings (Dabl and Ras-
rtiussen 1956) a detailed archaeologic-geological investigation
of the area around Tjørnuvík was desired. This small article
can be considered as one of the preliminary works for this
examination.
1. The main purpose of the geoelectrical examination has
been in various places to determine the depth to the border
of the sediment cover against the underlying basalt. According
to usual practice the measurements were carried out in accor-
dance with the electrical sounding method. (See for example
Sorgenfrei 1955, Kunetz 1966).
2. An electrical sounding ís measured by rneans of four
electrodes placed symmetrically on a straight line in the ter-
rain. During the measuring the uttermost electrodes are ex-
panded while the innermost are kept steady with a short
mutual distance (Schlumberger configuration Fig. 1).
K Q -H
L/2 ---------►
Fig. 1: Thc Schlnmberger electrode configuration.
By measurement of an electrical sounding the apparent
specific resistivity oa (expressed in ohm-m) of the earth is
determined. The dependence between oa and the electrode
distance (expressed by L/2 m, Fig. 1) reflects essentially the
vertical variations in the underground. It is generally believed