Fróðskaparrit - 01.01.1982, Page 42

50 Some Magnetotelluric Measurements on the Faeroe Islands
of electromagnetic waves on the earth, induced by alternating
electrical current, situated in the ionosphere. These waves,
when reaching the ground, induce secondary electromagnetic
waves in the subsurface, which are superposed on the imp-
ingent, primary, electrical, and magnetical fields. The nature
of the resulting fields is determined by the primary waves and
the electrical resistivity configuration of the earth, and by
measuring the horizontal electrical and magnetical field com-
ponents at the surface, the transfer functions, characterizing
the resistivity structure of the earth can be found.
In this paper we show the results in terms of apparent resi-
stivities gj, as a function of the period T in the N-S and
E-W directions, calculated from the transfer functions. The
apparent resistivity gives the true resistivity when measured
above a homogeneous earth, but otherwise a dependence with
the period is seen, which reflects an increased depth of penetra-
tion with increased period.
A first approximation proposed by Bostick (Weidelt, 1979)
for interpretation of the apparent resistivity curve from a
horizontal, stratified earth in terms of resistivities o B2, Qm
with depth z[( has been employed to our data. This interpre-
tation shows only the general resistivity level, and rapid fluctu-
ations in the curve are expected when bad quality data are
present.
The two measuring directions were placed in the magnetic
N-S and E-W directions, corresponding to 13°W and 77°E
from the geographic North.
For further details about the data analysis and the results,
reference is made to Rasmussen, Nielsen, and Pedersen (1981).
Results
Station FAE03 (2—500 secs) — Saksunardalur.
An analysis of the data from this station indicated that the
resistivity structure is 3-dimensional. A complex structure is
also seen in the plot of the apparent resistivities (fig. 1), where
decreasing difference between apparent resistivities in the N-S