The 1986 GPS survey of Iceland aimed to: (1) establish geodetic contro
l in the South Iceland Seismic Zone (SISZ), to study destructive earth
quakes there, (2) measure a country-wide network to form the basis of
a new first order national network. 51 points were surveyed, with 20-3
0 km spacings within the SISZ and 100 km spacings elsewhere. The data
were processed using the Bernese GPS software Version 3. Analysis was
difficult due to poor satellite geometry and short-period ionospheric
variations. However, an ambiguity-fixed, ionosphere-free solution gave
accuracies of 1-2 cm in the horizontal and 2-3 cm in the vertical for
the SISZ network and an ambiguity-free, ionosphere-free solution yiel
ded accuracies of about 5 cm for the country-wide network, An ionosphe
re-free solution for the total survey with ambiguities fixed for the S
ISZ network only gave marginal additional improvements over the two se
parate solutions. GPS surveying has continued annually in Iceland with
measurements in South Iceland in 1989 and 1992 (Hackman 1991; Sigmund
sson 1992) and in North Iceland in 1987, 1990 and 1992 (Jahn et al. 19
92; Foulger et al. 1992).