## 4 Results and Discussion
### Interpretation of the Observed Ground Deformation
In this regard, seasonal signals are commonly observed in surface deformation records in other sites worldwide (e.g., [63]), with annual or even semi-annual periods and different amplitudes from negligible to significant, depending on their driving causes. Future ground deformation investigations in Methana could be focused on identification and removal of such periodical terms via advanced time series processing. This operation would better enhance the long-term deformation behaviour of the observed sites which, in this case, may be partly concealed by these fluctuations. Higher LOS velocities (e.g., -5.0 to -10.0 mm/year) have been observed along steep valleys, mainly on slopes with east orientation (Figure 11a), where visibility of the ascending mode LOS eases the detection of downslope mass movements. The observed displacement could therefore be related to extremely to very slow mass movements and slope instability affecting rugged terrain and volcanic landforms that are recognized as prone to landslides and rock-falls [18]. Some seasonal fluctuations are also detected in the time series (Figure 11b). Figure 8: (**a**) LOS deformation velocity in 2015–2019 from the MT-InSAR analysis, (**b**) example of time series for a PS located on limestone, (**c**) geology/lithology and (**d**) urban footprint of Methana town: (**a**,**c**,**d**) are overlapped onto satellite optical imagery (© 2020 TerraMetrics, © 2020 Google). When the evidence from the MT-InSAR investigation is integrated with the outcomes of the GNSS data analysis (see Section 4.1), it can be suggested that the ground motions that are observed from 2015 to 2019 are compatible with the anticipated \"low\" volcanic activity of Methana. This comes out very evidently from the PS dataset and the generally low \(V_{\text{LOS}}\). Despite the low point density and spatial coverage of the volcanic edifice, the overall spatial distribution of the PS deformation values does not reveal a deformation field that could be reliably attributed to a typical volcanic inflation/deflation dynamic of the whole Methana, as found in the literature for other active volcanic areas. On the other hand, the DS dataset may suggest the presence of more widespread deformation patterns along the eastern flank. However, there are only few cases where the observed motions associate with specific landforms (e.g., narrow valleys, erosion gullies and superficial slides). In this regard, the photo interpretation of the slopes through Google Earth optical imagery did not highlight specific circumstances worth further investigation. Figure 9: (**a**) LOS deformation velocity over Vathi and Paleokastro in 2015–2019 from the MT-InSAR analysis overlapped onto satellite optical imagery (© 2020 TerraMetrics, © 2020 Google) and (**b**) example of time series for a PS located near Vathi town. Figure 11: **(a)** LOS deformation velocity over the southern portion of Methana peninsula in 2015-2019 from the MT-InSAR analysis overlapped onto shaded relief of the 5.5-m digital surface model by the Hellenic Mapping and Cadastral Organisation and (**b**) example of time series for a DS located in the SE part of Methana peninsula. Figure 10: **(a)** LOS deformation velocity over Mavri Petra in 2015-2019 from the MT-InSAR analysis overlapped onto satellite optical imagery (c) 2020 TerraMetrics, © 2020 Google) and (**b**) example of time series for a PS located in the NW portion of Mavri Petra. Due to the lack of strong seismic events (Mw > 4) or intense seismicity in the area of Methana peninsula (see Section 4.2), the observed ground deformation could not be associated with the recorded seismicity. There are active seismic zones in the vicinity of the peninsula; however, neither the location, the depth nor the magnitude of these events could be directly associated with the observed motions. Even if a seismic contribution to triggering superficial mass movements was present, this would be plausibly limited to nearby seismic swarms.