1) The permanent GPS network in Iceland offers the opportunity to observe temporal variations in crustal deformation fields. The measurements show the plate motions and transients due to earthquakes and volcanic activity.
2) Data from the ISGPS network are automatically collected and processed on a daily basis. Scaling factors for the formal errors were estimated 4.0 for the east and north coordinate components and 2.5 for the vertical component.
3) Vertical offsets of 20 mm downwards are observed when SCIGN radomes are installed. No significant horizontal offsets are detected due to radome installation.
4) Velocities are determined for the ISGPS stations. The interseismic horizontal velocities are generally in agreement with the NUVEL-1A plate movement model which predicts that the North-American and Eurasian plates are moving apart in Iceland at a rate of 19.6 mm/yr.
5) Stations REYK, OLKE, SKRO and AKUR are on the North-American plate and stations HOFN, HVOL, RHOF, SOHO, THEY, VMEY and VOGS are on the Eurasian plate. Stations HVER, HLID and KIDJ are within the plate boundary deformation zone moving at intermediate rates.
6) Vertical movements show that all stations are moving up relative to REYK at rates ranging from 3 mm/yr to 9 mm/yr.
7) No conclusive signs of intrusive activity in the Hengill area are observed since the stations in the area were installed in the spring of 1999.
8) No signs of intrusive activity in Eyjafjallaj÷kull are detected at station SOHO which was installed in September 1999, nor THEY which was installed in May 2000. Thus we conclude that the intrusion event in Eyjafjallaj÷kull that started in July 1999, had ended or was mostly over in the fall of 1999.
9) A prominent southward movement is observed at stations SOHO and HVOL near Katla volcano during the period August 2000 to December 2001. SOHO is moving southwards at 7 mm/yr during the period. Enhanced southward motion during July to August 2001 is also observed. These movements are interpreted as a magma pressure increase beneath the volcano.
10) Displacements due to the Hekla 2000 eruption were detected at stations SOHO and HVOL. SOHO recorded 7 mm horizontal motion towards Hekla during the eruption.
11) Coseismic displacements are observed at the times of the June 17 and June 21, 2000, earthquakes in the SISZ. Cosesismic displacements at stations west of the June 17 earthquake include displacements due to triggered events on Reykjanes peninsula and possibly in the Hengill area. The displacements for the June 21 earthquake fit well to a model based on network GPS measurements.
12) Periodic signals, with a period of approximately 1 year, are discernible in east and vertical components of the time series at most stations. The origin of the movements, i.e. whether they are measurement artifacts or a real signal from the earth, remains uncertain.