## 1 Introduction
The APE model attributes the SWS properties to the balance between the pore-fluid pressure and the local stress field, particularly its maximum horizontal component, \(\sigma_{\text{Hmax}}\)[19; 20]. It also ascribes variations of the SWS parameters to stress field changes, enabling their correlation with fluid processes, such as diffusion. Changes in the microcrack orientations or fluid saturation have been related to pore-pressure diffusion mechanisms associated with precursory stress-load on faults or post-seismic fluid release [21]. In Greece, a significant number of SWS studies have been performed. In the Eastern Gulf of Corinth [22; 23; 24], the Santorini Volcanic Complex [25] and Marathon [26], upper-crust anisotropy was attributed to the presence of stress-oriented fluid-filled microcracks, according to the APE model. However, there have also been observations where SWS has been related to CO\({}_{2}\) degassing processes [27]. Since 1990, studies in the WGoC have revealed a relation between \(\sigma_{\text{Hmax}}\) and the polarization direction of the fast S-waves (e.g., [11; 28]). Since 2000, with the installation of the CRL network [3], the large amount of recorded microseismic events has rendered the region an ideal site for the study of variations of the SWS parameters. In this work, we present a high-resolution earthquake catalogue of \(\sim\)9000 events for the WGoC during 2013-2014, along with a large dataset of shear-wave splitting parameters. This period is characterized by several seismic swarms and mainshock-aftershock sequences, presenting complex dynamics. We apply double-difference relocation to reduce the relative location uncertainties between clustered events and to enhance the spatial resolution of the catalogue. We examine the spatiotemporal evolution of seismicity, focusing on earthquake migration patterns. We examine phenomena related to the diffusion of fluids or aseismic creep by means of earthquake migration speeds, hydraulic diffusivities and diffusion exponents, with respect to potential origin points of fluid injection. The above are studied in conjunction with the temporal variations of the SWS parameters,focusing on periods characterized by the occurrence of seismic swarms or major events producing aftershock sequences. We determined more than 2000 fast shear-wave polarization direction and time-delay measurements over a period of two years; a number significantly larger from what is included in most upper-crust SWS studies. The wealth of measurements ensures the validity and the reliability of the herein presented results. We examine the spatial distribution of relocated hypocenters through detailed cross-sections and provide a 3D interactive visualization to showcase the relation between the inferred activated structures at depth and the mapped faults on the surface. The present study aims to provide a high-resolution view of the active fault geometries in the WGoC and their interplay, as seismicity migrates from one structure to another. We further investigate and discuss the possible triggering mechanisms of seismicity associated with the observed migration patterns, providing further insights from the SWS analysis of the upper crust in the area of the WGoC.