1325 ENVIRONMENTAL ENGINEERING May 22-23, 2008 The 7 th International Conference Faculty of Environmental Engineering Vilnius Gediminas Technical University Saulėtekio ave 11, LT-10223 Vilnius, Lithuania Phone: +370 5 2745090; Fax.: +370 5 2744731; e-mail: ap2008@ap.vgtu.lt POSTGLACIAL LAND UPLIFT IN ESTONIA BASED ON GEODETIC MEASUREMENTS ON PÕLTSAMAA-LELLE LEVELLING LINE Tarmo Kall, Harli Jürgenson Estonian University of Life Sciences, Institute of Forestry and Rural Engineering Kreutzwaldi 5, 51014 Tartu, Estonia E-mail: tarmo.kall@emu.ee harli.jyrgenson@emu.ee Abstract. Postglacial rebound in well-known and widely studied phenomena in Fennoscandia and also in Estonia. In order to study this phenomena and local crustal movements in the Põltsamaa-Lelle region, the 74 km long experimental line was established along the levelling line of national levelling network. During 1961-1987 regular high precision levellings with interval 3-8 years were performed on that line. Levelling line is very suitable for studying postglacial rebound because its direction is perpendicular to land uplift isolines and also it is sufficient for studying vertical movements related to tectonic faults because several of them are crossing with the line. In 2006 new levelling measurements were made on Põltsamaa-Lelle line in connection with renovation works of Estonian levelling network. Also there is high precision GPS measurements performed on that line in 1997 related to establishing national geodetic network and repeated in 2005 and 2007 according to study the crustal deformations on the line. Using additional data, specified value of the land uplift on Põltsamaa-Lelle levelling line was determined. Keywords: postglacial land uplift, levelling, GPS, tectonic activity. 1. Introduction. Subject of this study is determination of postglacial rebound on 74 km long Põltsamaa-Lelle levelling line (Fig. 1a) using high precision levelling and GPS measurement data. Using this levelling line in the present case is convenient because the direction of levelling line is perpendicular to isolines of postglacial rebound. Previous investigations of postglacial rebound of Earth’s crust and local tectonic movements using high precision levelling data and compilations of maps of vertical movements of Earth’s crust for Estonia or for the whole Baltic were carried out by Zhelnin [29], Vallner and Zhelnin [33], Vallner, Sildvee and Torim [32], Randjärv [23, 24], Torim [31], using sea level records by Jakubovski [9] and Jevrejeva et al [10]. Maps of Fennoscandian postglacial rebound (including also the territory of Estonia) were compiled by Ekman [2], Lambeck et al [18], and Vestøl [35]. Using only GPS- data, the Fennoscandian postglacial rebound were determined by BIFROST project [11]. Vertical movements of Earth’s crust and changes of gravity on Põltsamaa-Lelle levelling line were investigated by Kall and Oja [13] and Oja [21, 22]. On similar geodynamic line in Finland the changes of gravity and vertical movements of Earth’s crust were studied by Mäkinen [20] and Ekman and Mäkinen [3]. Compared to earlier similar investigations we had in the present study the opportunity to use additional high precision levelling data from 2006 and also GPS measurements made in 1997, 2005 and 2007 on the four Estonian geodetic reference network points along Põltsamaa-Lelle levelling line. In order to determine the long term vertical movement of Earth’s crust we used height differences of common sections to all levelling years. All levelling data were checked for presence of random and systematic errors and if needed systematic errors were removed. Also the weights for height differences were calculated. For determination of vertical movements the linear fitting between height differences and levelling years was calculated. Slope of this fitting gave the value of long term vertical movement by sections. By sum up of those slopes the velocities of vertical movement of benchmarks in relative to Põltsamaa fundamental benchmark were obtained. From GPS-measurements carried out in 1997, 2005 and 2007 the vertical movement between Põltsamaa and Lelle was determined in order to check the vertical movement value obtained from levellings. 2. Geological basement. Crystalline basement of the levelling line is formed mainly by amphibole gneiss, amphibolite and pyroxene gneiss, which belongs to complex of metamorphic rocks of South-Estonia and West-Estonia [14]. Depth of the sedimentary rocks reaches up to 320-360 meters and are formed mainly by Ordovician and Silurian carbonate