Jökull - 01.12.2007, Side 56

Þorbjarnardóttir et al.
Figure 9. Earthquake activity in the Herðubreið and Herðubreiðartögl area in 2005 and 2006. The earthquakes
within three swarms are based on relative location analysis. The relative error in latitude, longitude and depth
is less than 200 m. Focal mechanisms are shown for the largest earthquake in each swarm, each denoting left-
-lateral movement along northeasterly striking planes. – Afstæðar staðsetningar skjálfta í þremur hrinum við
Herðubreið og Herðubreiðartögl 2005 og 2006. Brotlausnir stærstu skjálftanna í hverri hrinu gefa til kynna
vinstri handar sniðgengishreyfingar á NA-lægum misgengjum.
planes. In 2005, seismicity in the area was also pre-
dominantly swarm activity. But, unlike 2006, it was
confined to a single swarm, southwest of Herðubreið.
Using the same relocation method and calculating the
focal mechanism of the largest earthquake, we find
that the same applies: that is, the earthquakes de-
note left-lateral movement on a northeasterly striking,
near-vertical fault plane (Figure 9).
During July and August 2006, Soosalu et al.
(2007) deployed a dense network of broadband seis-
mometers in the Askja-Herðubreið area. Combined
with the data of the SIL system, over 1,800 lo-
cal earthquakes were detected. The majority were
sourced beneath Herðubreið and Herðubreiðartögl at
depths of 2–7 km, marking the thickness of the brittle
upper crust in that region. Soosalu et al. also recorded
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