## 4 Discussion
### Seismic Anisotropy in the WGoC  
The comprehensive dataset of shear-wave splitting parameters of the present study may provide evidence regarding changes in the local stress field, fluid diffusion or saturation that can affect the anisotropic properties of the medium. Previous upper-crust anisotropy studies in the WGoC have focused in the 2010 Efpalio sequence [74], the 2013 Helike swarm [75] and the November 2014 sequence [48]. Their findings indicate that the fast shear-wave polarization directions are consistent with the maximum horizontal stress component, \(\mathrm{\sigma_{Hmax}}\) (e.g., [76]), which is in a WNW-ESE direction, parallel to the strike of major normal faults. Herein, the obtained mean \(\varphi\) directions are collectively presented in Figure 10. Notably, the results of the automatic analysis are, on average, consistent with those of [48; 75], who performed manual SWS measurements through visual inspection of polarigrams and hodograms. In the following, the presented average values of the SWSparameters are from measurements of Cat1, unless specified otherwise. These measurements concern the volume between the sources and the receiver as sampled by the seismic ray-paths, whose length is used for the normalization of the time-delays. In addition, we provide SWS measurements for stations in the WGoC that were not analyzed previously, such as AIOA, HELI and TEME in the south, as well as PANR and PSAM (Cat3 only) in the north. Station TEME presents a NW-SE \(\overline{\varphi}\) direction (145.1\({}^{\circ}\)\(\pm\) 16.3\({}^{\circ}\)), which does not appear to be consistent with \(\sigma_{\text{Hmax}}\) or the strike of local structures, but is similar to that of LAKA (\(\overline{\varphi}\) = 134.7\({}^{\circ}\)\(\pm\) 5.9\({}^{\circ}\)), to the west. On the other hand, HELI, a temporary station installed to record the 2013 Helike sequence [6], exhibits a WSW-ENE \(\overline{\varphi}\) direction (77.6\({}^{\circ}\)\(\pm\) 11.6\({}^{\circ}\)) that is similar to that of the neighboring AIOA station to the south (\(\overline{\varphi}\) = 79.4\({}^{\circ}\)\(\pm\) 7.7\({}^{\circ}\)). However, the \(\overline{\varphi}\) value at station HELI deviates from the direction indicated by the largest percentage of \(\varphi\) measurements, which is -E-W, as can be observed from the respective rose diagram (Figure S16), with a secondary SW-NNE \(\varphi\) direction. Stations AIOA and HELI are related with the epicentral regions of the 2001 Agios Ioannis [4; 49] and 2013 Helike [6; 48] swarms, both being either directly or partially related with the re-activation of older structures, which are not optimally oriented to the present-day stress-field. Specifically, the 2001 Agios Ioannis swarm has been attributed to the Kerinitis fault (Figure 1), with a strike that is SW-NE to WSW-ENE, consistent with \(\overline{\varphi}\) measured at AIOA and HELI. The \(\overline{\varphi}\) direction measured at TEME, however, is almost perpendicular to that of its neighboring station HELI, although the stations are located in close vicinity (\(\sim\)2 km apart). In the north, the \(\overline{\varphi}\) directions at stations TRIZ, PSAR and PSAM are nearly E-W, consistent with both \(\sigma_{\text{Hmax}}\) and fault orientations. An important difference was previously observed at stations PYRG and SERG, with \(\overline{\varphi}\) oriented SW-NE, a deviation that was  
Figure 10: Map of candidate events for SWS measurements from Cat1 (manual only) in the WGoC during 2013-2014. Blue lines represent the average fast S-wave polarization direction, \(\varphi\) (orientation), and time-delay, \(t_{\text{d}}\) (length), at the respective station (triangle, coloured according to network code). Coloured circles correspond to events with valid SWS measurements (grade A to C), whereas gray circles are events without valid measurements (only D, E or null). Red lines depict the respective mean polarization direction derived from Cat3 (see also Figure S18 in the Supplementary Material).