Ground deformation monitoring in the Ranafjord area of Norway by means of the permanent scatterers technique

Although Norway is situated along a passive continental margin, it is not devoid of tectonic activity. Several studies have documented significant movements along faults within the last 10-12 ka. Most of such movements probably occurred shortly after deglaciation, when rates of crustal rebound were very high. Nonetheless, current seismicity along the Norwegian coast suggests that crustal deformation is still taking place. Ranafjord, in northern Norway, is a region with higher than average seismic activity. A six-station seismic network installed by NORSAR detected numerous earthquake swarms in the area. In order to retrieve further crustal deformation data relative to Ranafjord it was decided to use differential SAR interferometry (DInSAR). The application of conventional DInSAR is extremely challenging because the expected deformation rates are low (a few mm/yr) and over long time spans phase coherence is not preserved on large portions of the area to be investigated. The Permanent Scatterers (PS) technique overcomes these drawbacks by exploiting long series of ERS data. At Permanent Scatterers, i.e. individual phase stable point-wise radar targets, displacement data can be retrieved with millimetric: accuracy. The PS grid can be seen as a high spatial density natural geodetic network. Thirty-seven ERS scenes covering the time span 1992-2000 were involved in a Permanent Scatterers (PS) analysis.