## 1 Introduction  
The Western Gulf of Corinth (WGoC), located in Central Greece, is one of the best-monitored seismogenic sites in Europe. Its high deformation rate (14-15 mm\(\cdot\)yr\({}^{-1}\) extension in a N9\({}^{\circ}\)E direction; [1, 2]) is the driving force of the intense microseismic activity that has been recorded by the Corinth Rift Laboratory (CRL) local seismological network since 2000 [3]. The background microsecinicity is interspersed by seismic swarms (e.g., [4, 5, 6, 7]) and earthquake sequences [8, 9, 10]. The WGoC has been the site of major events, with the most recent one being the 15 June 1995 \(M_{\rm s}\) = 6.2 Aigion earthquake [11]. The Gulf of Corinth is an active continental rift, formed by conjugate E-W-trending normal faults (Figure 1; [12, 13]). Major structures of the southern flank of the WGoC include the north-dipping Aigion, Helike and Pirgaki faults, as well as the Pathopyrgos fault [14], linked with the Aigion fault via the _en echelon_ Lambiri, Selianitika and Fasouleika NW-SE to WNW-ESE-trending fault segments (Kamarai fault system [11]). In the Greek Database of Seismogenic Sources [14], the Aigion fault is represented by a crustal-scale individual seismogenic source (GRIS503; Figure S20), whereas the Fasouleika and Selianitika faults are minor branches. Opposite to these structures, at the northern shore, the SW-NE-trending, SE-dipping Platanitis and Nafpaktos faults are mapped. Towards the east, the south-dipping Marathias and Kallithea faults are aligned E-W and WNW-ESE, respectively. Another south-dipping structure to the north of Marathias is the Trikorfo fault [14], extending eastwards to the Sergoula fault [15]. Offshore faults have also been mapped, such as the south-dipping Trizonia fault, the West Channel fault and the North and South Eratini faults [16; 17]. The background seismicity in the WGoC is scattered with epicenters, mainly located offshore between Aigion and Trizonia Island, but also north of the Psaithopyrgs fault. Background seismicity rates are of the order of 10 events/day, automatically detected by the local CRL network, reaching hundreds of events/day during earthquake swarms or aftershocks [5; 8]. This seismic activity, driven by high strain-rates, is associated with a fragmented seismogenic low-angle, north-dipping layer below the gulf, where the major normal faults of the region are rooting. Within the background seismic activity in the WGoC, long-term repeaters have been identified, associated with recurring slip on the same fault patch over the course of several years [9]. Such observations indicate the existence of small asperities surrounded by a partially creeping fault surface. Onshore seismicity is mostly projected towards the northern shores, near Effpalio and Eratini, mainly associated with activity at the deeper part of a north-dipping growing detachment (e.g., [8; 9]). Herein, we investigate the spatiotemporal evolution of the earthquake activity in the WGoC and examine patterns that could be associated with the involvement of aseismic factors driving the seismicity, such as propagating fluids or creeping of the surrounding fault surface. For this purpose, we also examine the anisotropic properties of the crust in terms of their statistics and temporal variations, which could be related with alterations in the level of stress or pore space fluid saturation. Seismic anisotropy in the upper crust is usually attributed to the presence of microcracks with a specific orientation [18]. As shear-waves propagate through an anisotropic medium, the Shear-Wave Splitting (SWS) phenomenon occurs, producing a fast shear-wave (S\({}_{\text{fast}}\)) that becomes polarized to the direction favored by the medium's anisotropic properties, whereas a slower one (S\({}_{\text{slow}}\)) is polarized to a perpendicular direction. The Anisotropic Poro-Elasticity (APE) model considers the presence of vertical, fluid-saturated microcracks in the upper crust, taking into account the influence of the physical properties of the fluids [18].