Summary

The Icelandic Meteorological Office operates a network of continuous GPS stations called ISGPS. The network was initiated as a collaborative project in 1999, to monitor crustal movements in active tectonic and volcanic areas in Iceland. There are presently 18 continuous GPS stations in Iceland, of which 14 belong to the ISGPS network, three are IGS stations and one is operated by the National Land Survey of Iceland. The design of the ISGPS network is aimed towards simplicity, robustness and cost-efficiency. The number of electric components in the field is minimized and we use a stainless steel quadripod monument design to achieve high monument stability. Data from the ISGPS stations are automatically downloaded and processed on a daily basis. We use the Bernese V4.2 software to process the data. The data are initially processed using predicted satellite orbits, and then reprocessed with CODE final orbits. In this study data from the continuous GPS stations during March 1999 through December 2001 are used. The time series from most ISGPS stations are dominated by motion caused by plate spreading across Iceland, in general agreement with the NUVEL-1A plate motion model. Discrepancies are observed at stations which are within the plate boundary deformation zone or close to volcanic deformation sources. Transient signals caused by an eruption in Hekla in February 2000, are observed. The nearest station, located 50 km from Hekla, recorded 7 mm horizontal motion towards Hekla during the eruption. Time series from stations located near Katla volcano indicate there is a slow pressure increase beneath the volcano. Two magnitude M_W=6.5 and M_W=6.4 earthquakes spaced 17 km apart occurred on June 17 and June 21, 2000, in the South Iceland seismic zone. Although most of the ISGPS stations were not located close to the epicenters at the time, a clear deformation signal was detected at all operational stations. The coseismic displacements for the June 21 event fit well to a source model based on network GPS measurements. The observed displacements for the June 17 event include deformation from triggered events on Reykjanes peninsula. The ISGPS network has proven to be a valuable tool to monitor crustal deformation and timing of deformation events.