Greinar (Vísindafélag Íslendinga) - 01.01.1976, Side 9

ELECTRICAL RESISTIVITY OF LAYER 3
IN THE ICELANDIC CRUST
AXEL BJÖRNSSON
National Energy Authority, Department of Natural Heat
Laugavegur 116, Reykjavík, lceland
ABSTRACT
The electrical resistivity of the oceanic layer “layer 3” in the Icelandic cruslt
has heen measured in situ with electrical and magnetotelluric methods. Outside
the active zone of spreading and volcanism the resistivity in the upper part of
layer 3 is 150-1000 Qm. It is concluded that the layer there must he saturated
with water. Beneath the neovolcanic zone much lower resistivity, about 10-
20 Qm, is caused by higher temperatures and probably somewhat higher porosity.
1. EVTRODUCTION
An active zone of rifting and recent volcanism, the neovolcanic
zone, crosses Iceland from south-west where it connects with the
Reykjanes ridge, to the north-east where it connects with the Ice-
land — Jan Mayen ridge along a fracture zone (1). It has a north-
south direction in NE-Iceland and splits up in two separate zones
in Southern Iceland having NE-SW direction. In Northem Iceland
the active zone is expected to have been situated in the Langjökull-
Skagi region until ahout 4 million years ago when it shifted ca
150 km eastwards to the present position (2). On both sides of the
neovolcanic zone there are strips of Quatemary flood basalts fol-
lowed by Tertiary flood basalts in Westem and Eastern Iceland.
A detailed seismic refraction survey of the Icelandic cmst was
performed by Pálmason (3). According to his interpretation there
is a surface layer with P-wave velocities 2.0 — 3.3 km/s in the
active zone of rifting and volcanism. Beneath it there are two layers