Jökull - 01.01.2010, Blaðsíða 7

Fifteen years of CGPS in Iceland
From the daily solutions we can build time series
of the motion of the stations. The time series (Figure
2) show the temporal evolution of the station coor-
dinates in east, north and vertical components, rela-
tive to the ITRF05 reference frame (Altamimi et al.,
2007). Plate motion results in a linear trend in the hor-
izontal components, whereas offsets in the time series
are typically due to equipment changes, earthquakes
or volcanic activity. One example of a co-seismic off-
set is seen in the time series from HVER at the time of
the May 29, 2008 earthquakes (Figure 2). In general,
the daily scatter of the vertical component is higher
than for the horizontal components. Seasonal signals
are seen at many stations in the highlands, thought
to be caused by snow loading in winter and melt-
ing in summer (Geirsson et al., 2006; Grapenthin et
al., 2006). The time series can be detrended to re-
move the steady plate motion and offsets (Figure 3),
and annual and semi-annual signals can be filtered
out, or estimated and removed, to display deviations
from constant motion more clearly. Examples of de-
trended time series from stations north of Vatnajökull
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Figure 1: Time series of motion of selected CGPS stations in the ITRF05 reference frame. Each point in east, north, and
up represents a daily solution estimated from 24 hours of data using the GIPSY/OASIS II software in single-site position
mode with reprocessed final orbits and clock products from the Jet Propulsion Laboratory. The vertical lines in 2000 and
2008 denote the time of the earthquake sequences in the South Iceland Seismic Zone. Offsets due to the earthquakes are
observed most notably at VOGS and HVER, and a post-seismic decaying signal is evident in the north component of HVER
in 2008. The north component at SAUD during 2007 to 2008 is affected by the Upptyppingar-Álftadalsdyngja intrusion.
Sites moving towards west (negative slope in the east component) are moving with the North-American plate. Stations
in the highlands (SKRO, SAUD, and FJOC) are moving rapidly upwards with respect to the coastal sites. Uncertainties
are not shown for clarity, but points with uncertainties larger than five times the median uncertainty have been removed.
– Tímaraðir hreyfinga nokkurra samfelldra GPS stöðva í ITRF05 viðmiðunarkerfinu. Lóðréttar línur sýna tímasetningar
jarðskjálftahrinanna í Suðurlandsbrotabeltinu árin 2000 og 2008. Stöðin SAUD sýnir merki innskotsins við Upptyppinga
og Álftadalsdyngju á tímabilinu 2007–2008 í norðurþætti tímaraðanna. Stöðvar á hálendinu (SKRO, SAUD, FJOC) sýna
vel landris vegna bráðnunar jökla.
JÖKULL No. 60 7