It is long debated whether a relation exists between the tidal stress produced by the Moon and the Sun on the Earth crust and the occurrence of difference geologic events, in particular large earthquakes and volcanic eruptions. Clear evidence for this relation has been elusive for a long time. However, the analysis of more complete global earthquake catalogues has shown that a significant statistical correlation exists between earthquake sizes/frequencies and the tidal Sun-Moon influence. 

Like in the case of ocean tides, solid Earth tides are strongly modulated by local conditions and context. Underlying composition and structure, tectonics and surface geomorphology are factors that critically condition the response of the crust terrain to tidal perturbations.

Currently, local effects are not modelled for use in GNSS geodetics, PPP and OD&TS. However, their impact could be relevant and modelling them would mark the difference with other approaches. Only a systematic use of GNSS would allow local measurement of tidal distortion of terrain and modelling of local tidal effects. 
The local tidal effect model can then be correlated with existing geological events to forecast associated hazards.

The main objectives of the activity are:

• undertake a step forward in the assessment of geological hazards with implications in forecast strategies, providing a complementary observable as a contribution to earthquake forecast;
• use GNSS time series as a form to model local solid Earth tides;

The tasks to be performed will include:

• development, implementation and validation of GNSS Data Processing tools for the measurement of solid Earth tides;
• analysis and modelling of solid Earth tides and their relation with geologic events: seismic and volcanic events, landslides and avalanches The main results of the activity will provide a practical demonstration of the concept by:
• processing GNSS data captured in real scenarios to measure solid Earth tides;
• local modelling of solid Earth tides for the forecast and assessment of the risk of geologic hazards.

For this purpose, it is proposed to use worldwide data provided by the International GNSS Service (IGS) together with GNSS stations deployed in locations with identified geological hazards.

The proposed activity is supported by ESA’s GNSS Science Advisory Committee (GSAC).