Acta Geodynamica et Geomaterialia

Title: GEODETIC ASPECTS OF GPS PERMANENT STATION NON-LINEARITY STUDIES
Author: Bogusz Janusz
DOI: 10.13168/AGG.2015.0033
Journal: Acta Geodynamica et Geomaterialia, Vol. 12, No. 4 (180), Prague 2015
Full Text: PDF file (1.5 MB)
Keywords: GPS, wavelets, subduction zones, permanent station’s velocity
Abstract: This analysis is focused on the investigation on non-linearity in the GNSS (Global Navigation Satellite System) permanent stations coordinate time series with the use of wavelet transform. Standard applicable procedures for the determination of the velocity components are based on a GPS (Global Positioning System) time series assuming its linearity. Topocentric time series do not follow the stationarity, being a combination of the stochastic part composed of random relations as well as deterministic, strictly dependent on the past variations. Moreover, the assumption of trend linearity may result in the misestimation of its value with an influence on its uncertainty. One of the solutions to decompose the analysed time series is to apply wavelets. The daily displacement derived from GPS data covering approximately from 13 to 19 years for 5 permanent IGS (International GNSS Service) stations located in the tectonically unstable areas (subduction or spreading zones) were analysed to investigate long-term changes. The PPP (Precise Point Positioning) solutions generated at the JPL (Jet Propulsion Laboratory) using the GIPSY-OASIS software were used. The long-term trend was determined using wavelet decomposition based on the Meyer’s orthogonal and symmetric wavelet and R2coefficient of determination was used here to estimate how well data fits a statistical model. Although the discovered peak-to-peak amplitudes of non-linearity in the last approximation (denoted here as A9) are not as high (several centimetres) in comparison to linear approximation, they still remain variable in time and will have an influence on the station's linear velocity. It was found that the trend is definitely non-linear for the selected (North, East or Up) components. The verification was performed on a so called “double stations” LHAS/LHAZ (Lhasa, Tibet/China), with only 4 metres apart. Two stations located next to each other recording similar long-term changes at the same time strongly prove the possible trend non-linearity for stations in tectonically active areas. The GPS-derived velocity inversions using wavelet approximation could be successfully compared to the elastic deformation that was predicted e.g. with finite elements modelling that approximates the geometry of the subduction, spreading or transition zones.