Greinar (Vísindafélag Íslendinga) - 01.01.1976, Page 55

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In a search for the causative fault we note that two strong tec-
tonic trends are present in the area around Dalvík, a north-south
trend as expressed in the direction of most fjords and valleys in
North Iceland, and a west-north-west trend which is most obvious
in the topography of the peninsula east of Dalvík. The latter trend
coincides with the trend of the Húsavík and Grímsey faults which
are known to he associated with earthquakes. Furthermore, the
largest aftershock of the Dalvík earthquake of 1934 appeared to
have its epicenter east of the main shock, suggesting an easterly
trending fault (12). ÍWithout any further evidence it therefore
seems reasonable to assrnne that the 1934 earthquake was asso-
ciated with a slip on a WNW trending fault near Dalvík.
There is additional evidence to suggest that the fault of the
Dalvík earthquake continues to the east-south-east into the north-
em volcanic zone north of Lake Mývatn (near 65.7°N, 16.9°W)
and to the west-north-west to the mouth of Skagafjördur (near
66.1 °N, 19.5°W) thus forming a 130 km long fault or fault zone
with a WNW trend. To the ESE of Dalvík the trace of this sug-
gested fault is marked by a deep erosional valley the orientation of
which is clearly tectonically govemed. Close to Dalvík this valley
extends across the fjord Eyjafjördur and cuts the island Hrísey off
from the mainland. It is here that the 1934 earthquake occurred.
Farther to the ESE the trace of the fault becomes less clear as it
cuts across several N-S trending valleys. In the northern volcanic
zone still farther to the ESE a lineament with the correct ESE
orientation shows up on ERTS imagery of the area and appears
to coincide with a fault mapped by Saemundsson (13) north of
the Lake Mývatn. Two short faults with nearly the same trend
have also been mapped by Sigurdsson (14) in the area north-west
of Mývatn. On the peninsula to the west of Dalvík the trace of the
suggested fault is not as clear in the topography as it is to the east.
In this area, however, the geothermal areas line up in a very con-
spicuous way along the predicted trace of the fault. Out of 30
known low temperature geothermal areas on the entire peninsula
between Skagafjördur and Eyjafjördur 20 fall within 4 km of the
predicted trace (information from the files of the National Energy
Authority, 1974). It is well known that hydrothermal activity tends
to occur above dykes or faults where water can percolate easily