Long-Term Stability of the SIRGAS Reference Frame and Episodic Station Movements Caused by the Seismic Activity in the SIRGAS Region

The western part of the SIRGAS region is an extremely active seismic area because it is located in the plate boundary zone of six tectonic plates, namely the Pacific, Cocos, Nazca, North American, Caribbean, and South American plates. The frequent occurrence of earthquakes causes episodic station movements, which affect the long-term stability of the SIRGAS reference frame. Normally, these episodic events are taken into account in the frame realisation by introducing new position and, optionally, velocity parameters for the affected stations. However, this is not enough to guarantee the high precision required in a reference frame such as SIRGAS. Additional analyses about the post-seismic behaviour of the reference stations are necessary to allow the precise transformation between preseismic and post-seismic (deformed) frames. According to this, the paper presents an evaluation of the long-term stability of the SIRGAS reference frame including the comparison of the different SIRGAS realisations and the analysis of station displacements caused by earthquakes in the SIRGAS region. Special care is given to the events happened in Arequipa (on 2001-06-23, M 1/4 8.4) and Chile (on 2010-02-27, M 1/4 8.8). The analysis is based on the SIRGAS Continuously Operating Network (SIRGAS-CON). Beside analysing the station position time series and estimating the displacement vectors of the SIRGAS reference stations, some recommendations to mitigate the impact of this kind of events in the use of SIRGAS as a reference frame are formulated.