Jökull - 01.12.2007, Page 57

Seismicity in Iceland during 2006
100 small earthquakes concentrated at depths of 13–
27 km, suggesting that this seismicity is related to
magmatic movements in the lower part of the crust.
Tjörnes Fracture Zone
The Tjörnes Fracture Zone (TFZ, Figure 1) is a zone
of transform faulting north of Iceland. The seismicity
of this zone occurs mainly within two, WNW trend-
ing, seismic lineaments: the Grímsey lineament (GL)
and the Húsavík-Flatey Fault (HFF). Earthquakes also
occur within a third lineament, the Dalvík lineament
(DL). Earthquake sequences in the TFZ are very com-
mon and 2006 was no exception. Most sequences
took place within the GL, but the largest sequence was
a mainshock-aftershock sequence southeast of the is-
land Flatey, within the HFF (Figure 10). The sequence
commenced with a magnitude 4.2 mainshock on 1
November, which was felt in the north of the coun-
try at distances over 70 km from the source (Table 1).
Aftershocks were recorded from 1–5 November. Af-
ter relocation, the hypocenters clustered at depths of
around 11 km along a WNW striking plane dipping to
the northeast. The focal mechanism of the mainshock
suggests right-lateral movement of the fault.
Several earthquake swarms have been detected in
the last few years beneath Kaldbakur (Figure 1), on
the Dalvík lineament of the TFZ. The most numer-
ous swarm occurred in August 2006 with over a hun-
dred earthquakes, the largest registering a magnitude
of 3.5. In November a smaller swarm was detected in
the same area.
Figure 10. Mainshock-aftershock sequence along the Húsavík-Flatey fault plotted on a multibeam bathymetric
map of the seafloor, southeast of the island Flatey. The focal mechanism of the mainshock shows right-lateral
movement along a WNW-striking plane dipping to the northeast. – Skjálftaröð á Húsavíkur-Flateyjarmisgeng-
inu, suðaustur af Flatey. Brotlausn meginskjálftans sýnir hægrihandar sniðgengishreyfingu á VNV-lægu plani
sem hallar til norðausturs.
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