Jökull - 01.01.2004, Side 67

Data report
Seismicity in Iceland 2003
Gunnar B. Guðmundsson, Steinunn S. Jakobsdóttir and Bergþóra S. Þorbjarnardóttir
Department of Geophysics, Icelandic Meteorological Office, Bústaðavegur 9, 150 Reykjavík, Iceland;
gg@vedur.is, ssj@vedur.is, begga@vedur.is
Abstract — In 2003 the SIL seismic monitoring network consisted of 41 seismic stations. The total number of
earthquakes located by the SIL system in 2003 was about 10400, which is the lowest number in the last 10 years.
However the number of earthquakes of magnitude greater than 1.5 was similar to 2002. Eight felt earthquakes
were reported in 2003. The largest earthquake in 2003 occurred about 7 km southwest of Kleifarvatn on the
Reykjanes Peninsula on August 23 at 02:00. It had a magnitude Mlw = 5 and was felt in many parts of SW–
Iceland. The aftershock activity was most intense the first two days after the main shock and culminated about
a week later. Seismicity beneath the Mýrdalsjökull glacier was high and as in 2002 was continuous throughout
the year under the western part. From mid year 2003 the seismic activity has increased at Grímsvötn volcano
in the Vatnajökull ice cap. Some earthquake swarms occurred on the northern part of the Reykjanes Ridge with
earthquakes greater than 4. Several earthquake swarms with earthquakes of magnitude about 3 were recorded
in the Tjörnes Fracture Zone. Aftershock activity still continues on the main faults from June 2000 in the South
Iceland Seismic Zone.
INTRODUCTION
The SIL seismic system is a network of 3-component
digital seismic stations and a data processing system
(Jakobsdóttir et al., 2002). At the end of the year 2003
the network consisted of 41 SIL seismic stations. One
new SIL seismic station, Krókóttuvötn, was installed
north of Mývatn in the middle of the year. Two sta-
tions were discontinued in January 2003, Skamma-
dalshóll, south of Mýrdalsjökull, and Grindavík, on
the Reykjanes Peninsula.
A total of 10400 earthquakes were located by the
SIL seismic system in 2003 compared with about
14000 in 2001 and 2002 (Figures 1 and 2). The num-
ber of earthquakes greater than or equal to 1.5 is sim-
ilar for the years 2003 and 2002.
The magnitude scale used here is our local mo-
ment magnitude scale Mlw (Slunga et al., 1984). It is
scaled in a manner resembling the Richter local mag-
nitude scale Ml.
Here we focus mainly on the seismic activity on the
Reykjanes Peninsula and beneath Mýrdalsjökull and
Vatnajökull, which had high seismic activity in 2003.
Following is a short description of the seismicity in
other areas during 2003.
0
5
10
15
20
25
30
35
40
N
um
be
r
of
E
ar
th
qu
ak
es
(
x1
00
0)
All eq.
Mlw > 1.5
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
Figure 1. Annual number of earthquakes from 1994
to 2003. – Árlegur fjöldi jarðskjálfta fyrir árin 1994
til 2003.
JÖKULL No. 54, 2004 67