Anthropogenically induced subsidence in Thessaly, central Greece: new evidence from GNSS data

Abstract

We combine almost 10 years of continuous GNSS observations at four permanent stations with groundwater and rainfall data to investigate subsidence patterns in the region of Thessaly, central Greece. Thessaly is a key area for studying anthropogenic versus tectonic subsidence in Greece because it is (a) characterized by overexploitation of groundwater reservoirs since the 1980s and (b) has a Twentieth-century history of shallow, normal-slip earthquakes with M > 6. We infer that anthropogenic subsidence continues at southeast Thessaly (Karla reservoir region) up to autumn of 2017 because the vertical time-series data of station STEF (Stefanovikio) reach a cumulative value of 55 cm and show a “ramp-flat” pattern that correlates with neighboring borehole data. The geodetic data from other three examined regions (city of Larissa, city of Karditsa and Klokotos) indicate ground stability. The GNSS stations in Karditsa (KRDI) and Larissa (LARM) show correlation with groundwater-level fluctuations but no subsidence. Station KLOK (Klokotos) shows a small subsiding trend (− 0.38 mm/yr) with no correlation to either groundwater levels or to rainfall patterns; therefore, its seasonal periodicity may reflect geodynamic (plate) motions.