Abstract
The seasonal signal determined by the Global Navigation Satellite System (GNSS), which is captured in the coordinate time series, exhibits annual and semi-annual periods. This signal is frequently modelled by two periodic signals with constant amplitude and phase-lag. The purpose of this study is to explore the implication of different types of geophysical events on the seasonal signal in three stages—in the time span that contains the geophysical events, before and after the geophysical event, but also the stationarity phenomena, which is analysed on approximately 200 reference stations from the EPN network since 1995. The novelty of the article is demonstrated by correlating three different types of geophysical events, such as earthquakes with a magnitude greater than 6° on the Richter scale, landslides, and volcanic activity, and analysing the variation in amplitude of the seasonal signal. The geophysical events situated within a radius of 30 km from the epicentre showed a higher seasonal value than when the timespan did not contain a geophysical event. The presence of flicker and random walk noise was computed using overlapping Hadamard variance (OHVAR) and the non-stationary behaviour of the time series of the CORS coordinates in the time frequency analysis was done using continuous wavelet transform (CWT).
Highlights
The Global Navigation Satellite System—Continuously Operating Reference Station (GNSS -CORS) network stations that are designed with excellent spatial density and distribution are used for various geodetic and non-geodetic applications [1,2,3,4,5]
The highest amplitudes due to seasonal variation were observed during periods that corresponds to one tropical year
The seasonal signal computed from a time series that contained a shallow earthquake event had a higher amplitude for only one of three stations within a radius of 30 km from the epicentre of the earthquake
Summary
The Global Navigation Satellite System—Continuously Operating Reference Station (GNSS -CORS) network stations that are designed with excellent spatial density and distribution are used for various geodetic and non-geodetic applications [1,2,3,4,5]. The estimation of seasonal changes of CORS positions plays an extremely important role, since it can impact the final estimates, the site velocity [6,7,8]. Three key categories can be defined in terms of potential contributors to the seasonal variation observed at CORS sites. Included in the first category are the influence of the gravitational excitation, primarily from the Sun and Moon, universal time corrected for polar motion (UT1—Universal Time) variation, rotational displacements due to the seasonal polar motion, loading-induced displacements due to solid Earth tides, ocean tides and the effects of atmospheric tides [9,10,11]. The second category of seasonal variation contains the thermal origin coupled with hydrodynamics [12].
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