Ground deformations along SW coast of the Gulf of Gdansk analysed using satellite radar interferometry

The paper presents results of SPINUA (Stable Point Interferometry over Unurbanised Areas) Persistent Scatterers Interferometry (PSI) processing chain to study Earth surface deformations along the SW coast of the Gulf of Gdañsk, along the SE part of the Baltic Sea. As the input for SPINUA techniques 40 descending ERS-1/2 SLC (Frame = 251, Track = 36) images from the period 1995-2001 has been used. The area of interest (AOI) includes few cities and several towns, villages and harbors. The low lying coastal areas of the SW part of the Gulf of Gdañsk are at risk of floods and marine erosion. The PSI results, however, did not reveal the presence of a regional scale, spatially consistent pattern of displacements. It is likely that any crustal deformations in the AOI simply do not exceed ±2 mm/year, which is the velocity threshold we assumed to distinguish between moving and non-moving persistent scatterers (PS). Importantly, for the most part the urban areas of the main cities (Gdañsk, Gdynia and Sopot) results show ground stability. Nevertheless, significant downward movements up to several mm/year, are locally noticed in the Vistula river delta - alluvial plain system located in the coastal zone east of Gdañsk as well as in the inland area west of the Gdañsk city. Indeed, the highest subsidence rates (-12 mm/year) was observed in the Gdañsk petroleum refinery constructed on alluvial sediments. Thus the anthropogenic loading and consolidation of the recent deposits can locally be an important factor causing ground subsidence.