Jökull - 01.12.2007, Page 51

Seismicity in Iceland during 2006
Figure 4. Relocated earthquakes in the Kleifarvatn area from 2000 (purple and green) and between 25 February
and 10 March 2006 (orange). The relative error in latitude, longitude and depth is less than 100 m. The thick
gray line indicates the approximate location of the fault plane of a magnitude 5 event in 2000. The yellow star
shows the location of the 2003 magnitude 5 mainshock. – Afstæðar staðsetningar skjálfta við Kleifarvatn 2000
(fjólubláir hringir og grænar stjörnur) og frá 2006 (appelsínugulir hringir). Afstæð skekkja í lengd, breidd og
dýpi er minni en 100 m. Gráa strikið sýnir staðsetningu brotflatar skjálfta að stærð 5, sem varð árið 2000.
Gula stjarnan sýnir staðsetningu meginskjálftans 23. ágúst 2003.
Hengill Region and South Iceland Seismic Zone
The Hengill region is at the junction of the Reykja-
nes Peninsula, the South Iceland Seismic Zone and
the Western Volcanic Zone (Figure 1). Intense seis-
mic activity, due to magma intrusion, characterized
the area between 1993 and 1998 (Rögnvaldsson et al.,
1996; Sigmundsson et al., 1997; Feigl et al., 2000;
Vogfjörð et al., 2005). After 1998, the seismicity rate
decreased substantially, but earthquakes remain com-
monplace in the region.
The largest earthquake sequence in 2006 in the
Hengill region occurred on 29 May, with about
80 recorded earthquakes. After relocation using a
double-difference method, the majority of hypocen-
ters clustered at 6 km depth along a 0.5 km verti-
cal fault, striking northeast. The focal mechanism
of the largest earthquake, with a magnitude of 3.2,
suggests right-lateral movement along the fault plane.
This outcome fits previous observations of the region,
where delineated faults mostly strike northeast and
east and dip predominantly near-vertical. Slip direc-
tions are generally right-lateral on northeast striking
faults and left-lateral on east striking faults (Vogfjörð
et al., 2005).
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