Jökull - 01.07.2003, Page 58

Bergþóra S. Þorbjarnardóttir, et al.
1991 - 2000
2001
Discontinued
NVZ
EVZSISZ
WVZ
Vatnajökull
Mýrdals−
jökull
Öxar−
fjörður
Eyja−
fjörður
Rid
ge
eskves
haf
bre fla
grf
Re
yk
jan
es
R
id
g
e
TFZK
o
lb
ei
n
se
y
Figure 1. The map shows the SIL seismic station network. The main tectonic featues of Iceland are also shown:
The Tjörnes Fracture Zone (TFZ), the Northern Volcanic Zone (NVZ), the Eastern Volcanic Zone (EVZ), the
Western Volcanic Zone (WVZ) and the South Iceland Seismic Zone (SISZ). – SIL jarðskjálftamælanetið ásamt
gos- og brotabeltum landsins. Tjörnesbrotabeltið (TFZ), nyrðra gosbeltið (NVZ), eystra gosbeltið (EVZ), vest-
ara gosbeltið (WVZ) og Suðurlandsbrotabeltið (SISZ).
MÝRDALSJÖKULL
Seismic activity beneath the Mýrdalsjökull glacier is
concentrated in two areas, within the Katla caldera
and in the currently more active Goðabunga area, in
the western part of the glacier. The seismicity under
Goðabunga has followed a seasonal pattern during the
last decades (Figure 4). The number of earthquakes
in the latter half of the year is many times higher than
in the first half. Two factors are likely involved, the
decreased load of the ice and the increased pore pres-
sure in the crust beneath the glacier. Einarsson and
Brandsdóttir (2000) argued that the pore pressure is
the more influential factor, causing fluctuations in the
brittle crust beneath the glacier.
In July of 1999 a minor magmatic event (Einars-
son, 2000) resulted in a small jökulhlaup in the river
Jökulsá á Sólheimasandi, southwest of the Mýrdals-
jökull glacier. A new cauldron was formed and other
known cauldrons in the glacier increased in size (Guð-
mundsson et al., 2000).
Changes have occurred in seismicity in the Goða-
bunga area over the last semesters. The activity in
2000 continued into the year 2001 and did not de-
crease until a few months later. The activity increased
again in August but at the end of the year it continued
with the same intensity the following months.
56 JÖKULL No. 52, 2003