Greinar (Vísindafélag Íslendinga) - 01.01.1976, Page 54

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resulting locations are listed in Table 2 and shown in Figure 2. The
last column in Table 2 gives the distance between the location in
Table 1 and that in Table 2. None of these distances are less than
10 km, and discrepancies larger than 20 km are common.
The relocated epicenters delineate a WNW trending linear zone,
probably a fault or a narrow fault zone. The location of this fault
is somewhat uncertain, but it probably passes within a few kilo-
meters of the island Grímsey. The fault possibly continues into
Iceland. Events number 1 and 2 in Table 1 occurred during an
earthquake swarm which was widely felt in NE Iceland. The loca-
tions of these events in Table 1 are confirmed by the felt reports
of the swarm and can be considered to be reliable. These locations
fall on the landward extrapolation of the Grímsey fault. It should
be noted, however, that no topographic or geologic evidence is avail-
able at the present to suggest a WNW striking fault in this part
of Iceland.
A focal mechanism solution was found for event No. 24 by F.
Klein (11) and is reproduced in Figure 3. The solution is of fair
quality and shows strike-slip faulting. One nodal plane strikes 25°
and dips 72° to the west, the other nodal plane has a strike of 112°
and dips 82° to the south.
The strike of the WNW striking nodal plane nearly coincides
with the trend of the fault as delineated by the epicenters. If that
nodal plane is taken as the fault plane the sense of faulting is right-
lateral. The Grimsey fault is thus shown to be a right-lateral strike-
shp fault.
OTHER FAULTS
We have now seen that a good part of the seismic activity in the
Tjömes Fracture Zone can be attributed to slip along the Húsavík
and Grímsey faults. Some of the seismic activity is clearly not as-
sociated with these faults, however. The Dalvík earthquake of Jime
2, 1934 (magnitude 6%), for example, caused extensive damage
in the village of Dalvík and vicinity (Figure 1). The epicenter of
that quake was estimated to be between Dalvík and the small island
Hrísey to the east of Dalvík (12). This estimate was based on
macroseismic observations.