Jökull - 01.01.2010, Blaðsíða 4

Geirsson et al.
INTRODUCTION
Iceland is a sub-areal exposure of the Mid-Atlantic
ridge, and the interaction of the plate boundary with
the Icelandic hotspot makes the 100 thousand km2
island effectively a natural laboratory for a wealth
of geophysical and geological processes. Many pio-
neering studies of crustal deformation have been con-
ducted in Iceland since the first geodetic network was
established in 1938 to test Wegener’s hypothesis of
continental drift and subsequent theories of plate tec-
tonics (Einarsson et al., 2006 and references therein).
With the first GPS survey in 1986, Iceland was one of
the first countries in the world where GPS was used
for precision geodetic studies of crustal deformation
(Foulger et al., 1993). Before the first continuously
operating GPS site in Iceland was installed in 1995,
a number of GPS campaigns had already been per-
formed, observing geodetic benchmarks for hours or
days to obtain a position in time to estimate surface
deformation caused by plate spreading, earthquakes
and magma movements.
Crustal deformation in Iceland is due to many dif-
ferent processes, acting at different spatial and tempo-
ral scales. A range of deformation signals have been
detected by the continuous GPS (CGPS) network.
These include plate motion, co- and post-seismic de-
formation in the South Iceland Seismic Zone (SISZ)
and the Reykjanes peninsula, time-varying deforma-
tion due to intrusive activity in Eyjafjallajökull vol-
cano and Upptyppingar-Álftadalsdyngja area, magma
accumulation in Hekla and Katla volcanoes, uplift
and subsidence in geothermal areas in Krísuvík and
Hengill, seasonal signals due to snow loading in win-
ter and melting in summer, and high rates of uplift in
central Iceland due to melting of the ice caps.
The general purpose of this paper is to present a
summary of results and observations from continuous
GPS measurements in Iceland during 1995 to 2010.
This paper is not intended to be an in-depth study of
any of the processes or events encountered, rather it
serves as a summary of recent and previously pub-
lished results obtained so far.
THE CGPS NETWORK
As of the beginning of 2010, there were 64 CGPS sta-
tions in operation in Iceland, mostly located within
and around the plate boundary (Figure 1). Continuous
GPS measurements began in Iceland in 1995 when the
IGS (International GNSS Service) station REYK was
installed in Reykjavík, followed by a second IGS sta-
tion, HOFN, in 1997. In 1999 the CGPS network ex-
panded significantly when six stations were installed
as part of a collaborative effort between the Icelandic
Meteorological Office (IMO) and the University of
Iceland (Geirsson et al., 2006). The Icelandic CGPS
network has been expanding rapidly since, with 16
more stations added to the network between 2000 and
2005, and more than 40 stations installed between
2006 and 2009.
Most of the network expansion during 2006–2009
resulted from a joint effort of several research groups
in Iceland, the United States and Switzerland. The
projects are funded by the Icelandic Research Coun-
cil, the US National Science Foundation (NSF), ETH
Zurich, University of Arizona, and The Pennsylva-
nia State University. The new CGPS stations form
sub-networks (Figure 1) that have been installed in
co-operation with the IMO, who operate a large part
of the CGPS sites in Iceland. The network operated
by IMO is called the ISGPS (Icelandic GPS) net-
work. The sub-networks are: (1) The North Iceland
network, with 10 CGPS stations installed by the group
from ETH Zurich; (2) The Central Highland of Ice-
land (CHIL) network, with 14 stations installed by the
group from the University of Arizona; (3) The Hekla
network with 6 stations installed by the groups from
The Pennsylvania State University and the Nordic
Volcanological Center; (4) The South Iceland Seis-
mic Zone and Reykjanes peninsula networks with 5
new stations installed by the groups from the Nordic
Volcanological Center and University of Arizona.
The National Land Survey of Iceland also oper-
ates a network of five CGPS stations, including the
two IGS sites (REYK and HOFN). These data are in-
cluded routinely in our data processing. In addition,
there are private and governmental single- and dual-
frequency networks in continuous operation intended
primarily for cadastral surveys and navigation of air-
4 JÖKULL No. 60