On the potential of InSAR EGMS data for the Analysis of Pre-Seismic Deformations

Understanding the spatiotemporal evolution of ground deformation preceding earthquakes is a key objective in contemporary seismotectonic research, as such deformation may reflect preparatory processes within the crust. Possibly preceding an earthquake event, variations in deformation rates and patterns prior to seismic rupture have been reported in different tectonic settings and are commonly interpreted in terms of stress accumulation, aseismic slip, or fluid-related processes along active faults. Satellite-based Interferometric Synthetic Aperture Radar (InSAR), particularly when exploited through long and spatially dense deformation time series, offers a unique opportunity to retrospectively evaluate these pre-seismic signals at wide-area scale.

In this context, this study highlights the potential of the European Ground Motion Service (EGMS) Ortho products for investigating pre-earthquake deformation behaviour. As an illustrative example, the Mw 6.3 Thessaly earthquake (central Greece, March 2021) is analysed using the first EGMS Ortho data release, covering the period from January 2016 to December 2021. The dataset provides vertical (Up–Down) and horizontal (East–West) deformation time series on a regular 100 m grid, enabling a homogeneous spatial assessment of deformation patterns.

Our results show that the spatial distribution of linear deformation velocities derived from two distinct temporal phases. The first phase (January 2016–March 2020) represents the long-term background behaviour and is characterised by overall stability and the absence of coherent deformation anomalies. In contrast, the second phase, covering the year preceding the earthquake (March 2020–March 2021), reveals a clearly distinguishable and spatially coherent deformation pattern concentrated around the epicentral area, indicating a marked departure from background conditions. Moreover, the resulting acceleration fields show a pronounced anomaly centred near the epicentre, particularly evident in the vertical (Up–Down) component. The horizontal (East–West) acceleration pattern is less pronounced but exhibits a block-like spatial organisation, characterised by sign changes across adjacent domains. This block behaviour is more evident in the East–West direction and comparatively weaker in the vertical component.

Overall, this example demonstrates that EGMS Ortho products can effectively capture subtle yet spatially structured changes in deformation behaviour prior to seismic events. These results underscore the value of EGMS as an open, continental-scale resource for systematic exploration of pre-seismic deformation patterns and their potential contribution to seismic hazard research.