Jökull - 01.12.1992, Side 7

M (a)
Figure 2. (a) Temporal distribution and magnitude of Askja earthquakes prior to and during the eruption in
October 1961; (b) Askja earthquakes on January 30, 1962; (c) and June 12, 1962. - Stœrðir jarðskjálfta í
tengslum við eldgosið í Öskju í október 1961 (a) og innskotavirkni í janúar og júní, 1962 (b og c).
in the northeastem part of the Askja caldera. During
the eruption, earthquakes big enough to be detected
on seismographs (> M 2.4) were recorded on October
26 and 28. The eruption ended in the beginning of
December and the estimated volume of the lava flow
is 0.09-0.1 km3 (Einarsson, 1962; Þórarinsson, 1963;
Sigvaldason et al„ 1992).
An earthquake swarm in the Askja region began on
January 30, 1962. The swarm lasted about two hours
and 12 earthquakes were recorded at the Kirkjubæj-
arklaustur seismic station. This earthquake activity
was more intense than during the October eruption al-
though no earthquakes reached magnitude 4 (Figure
2b). People in the Mývatn district reported increased
steam activity in Askja that day but geologists who
surveyed the region from an aircraft on January 31
could not detect any change in the geothermal activ-
ity (Þórarinsson, 1963). One Askja earthquake was
recorded on February 2 and during the next three
months 6 events were recorded with epicenters some-
where in the Askja region.
On June 12,1962, at 01:27 a magnitude 4.2 earth-
quake occurred in the Askja region. This earthquake
marks the beginning of a big swarm that lasted all
day, during which 70 earthquakes were recorded (Fig-
ure 2c), followed by 6 events later in June. In late
June 1962, a new fault was observed along the east-
ern wall of the Askja caldera. The fault extended from
Öskjuvatn north towards the eruption site from Octo-
ber 1961. The westem flank of the fault had subsided
by about one meter and the lake level of Öskjuvatn had
been lowered by about 3 meters (Þórarinsson, 1963).
The seismicity on January 30 and June 12 and the
subsidence observed along the eastern caldera wall
JÖKULL, No. 42, 1992 5