Abstract
Postglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.
Highlights
The International Gravity Reference System (IGRS) will be realized by absolute gravity observations and the comparisons between the absolute gravimeters that make the observations (Wilmes et al 2016; Wziontek et al 2021)
Due to the disappearance of past ice loads, the Earth’s crust is continuously rising, causing vertical velocities up to 1 cm/yr in Fennoscandia (Milne et al 2001). This postglacial rebound (PGR) process has been extensively studied with a variety of techniques, such as tide gauges (Ekman 1996), repeated precise levelling (Mäkinen and Saaranen 1998) and continuous observations using global navigation satellite systems (GNSSs) (Johansson et al 2002; Kierulf et al 2014; Lahtinen et al 2019)
We will use the gravity trends that have shown to be stable in time to study the relationship between gravity rates and uplift rates, from the semi-empirical land uplift model, and from GNSS time series, including the most recent GNSS solution from Lahtinen et al (2019)
Summary
The International Gravity Reference System (IGRS) will be realized by absolute gravity observations and the comparisons between the absolute gravimeters that make the observations (Wilmes et al 2016; Wziontek et al 2021). Due to the disappearance of past ice loads, the Earth’s crust is continuously rising, causing vertical velocities up to 1 cm/yr in Fennoscandia (Milne et al 2001). This postglacial rebound (PGR) process has been extensively studied with a variety of techniques, such as tide gauges (Ekman 1996), repeated precise levelling (Mäkinen and Saaranen 1998) and continuous observations using global navigation satellite systems (GNSSs) (Johansson et al 2002; Kierulf et al 2014; Lahtinen et al 2019).
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