Jökull - 01.12.2007, Blaðsíða 58

Þorbjarnardóttir et al.
Figure 11. Recorded intraplate earthquakes in the Western Fjords. Errors in latitude and longitude are shown.
–Mældir innflekaskjálftar undir Vestfjörðum. Krossar sýna breidd og lengd óvissu í staðsetningum.
Western Fjords
Intraplate earthquakes are known to occur in Borgar-
fjörður in southwest Iceland, the Western Fjords, and
at the edge of the eastern continental shelf (Einarsson,
1989). In 2006, a swarm of intraplate earthquakes
was recorded south of Reykjarfjörður on the Western
Fjords (Figure 11). These earthquakes are connected
with a Tertiary fault zone. A total of 22 earthquakes
were detected over a period of seven days from 7 to
13 of September. The largest earthquakes had mag-
nitudes of 3.4 and 3.2, but were not felt in the area.
Earthquake swarms in this region were also recorded
in 1964 and 1994. A few isolated earthquakes have
also been located in recent years.
CONCLUSIONS
1. Seismic activity in Iceland during 2006 was com-
parable to 2005, but slightly less than in 2001–2004.
About 9,500 events were located, of which 480 were
icequakes sourced in Skeiðarárjökull glacier in con-
nection with intense rainfall and a small jökulhlaup
from Grænalón. In addition, several hundred explo-
sions were detected.
2. The largest earthquake of the year, of magnitude
4.7, occurred east of Lake Kleifarvatn on the Reykja-
nes Peninsula in March, in an area of high seismicity.
The foreshocks, mainshock and aftershocks were lo-
cated along a northeasterly striking fault plane at 7.5–
9 km depth.
3. The largest earthquake sequence in the Hengill
region was a swarm of 80 earthquakes in May. The
earthquakes were located along a 0.5 km vertical
fault plane at 6 km depth. The focal mechanism
of the largest earthquake signifies right-lateral move-
ment along a northeasterly striking plane. Also in the
Hengill region, microearthquakeswere detected at the
construction site of a geothermal power plant. This
56 JÖKULL No. 57