Geodetic monitoring to a mine area

This paper presents results and remarks about the use of a GPS geodetic network for the monitoring of surface deformations ongoing in the region of Bages, Catalonia (Spain). The area under investigation presents an extensive salt formation (2100 km2) known as “Conca Potàsica”. The basin consists of a large block of potassium salts which were already used for extraction purposes in ancient times. Continuous underground and superficial mining from authorized private companies gave rise to a phenomena of subsidence in the past. This aggravated the existing natural subsidence caused by the dissolution of potassium and magnesium salts which affected many urban areas. By the second half of the twentieth century deformations of about one meter were recorded in this area. The GPS network consisting of 36 points distributed throughout the territory of Bages was firstly measured in December 2007, then a second survey took place in 2008. Results of this second campaign were compared to those of 2007 in order to detect surface deformations in the area of Bages. Statistical analysis of the position differences between the two epochs showed that significative displacements have occurred so far just for the sites actually located on thegeologically unstable subareas of the “Conca Potàsica”.