## 4 Discussion
### Physical Mechanisms for Earthquake Migration  
The temporal evolution of seismicity in the WGoC during 2013-2014 presents a series of bursts with significant earthquake migration patterns. The most characteristic one was observed in the offshore region between Nafpaktos and Psathopyrgos (group #4), mainly during July-October 2014, with migration speed in the range of 0.13-0.18 km/day eastwards and \(\sim\)0.07-0.12 km/day westwards (Figure S22c). The occurrence of the 21 September 2014 earthquake in the west produced an aftershock sequence that severely accelerated earthquake migration rates to over 1 km/day in its vicinity. Seismicity migration speeds of the order of 100 m/day are associated with fluid-driven seismicity, as observed in several cases in the WGoC (e.g., [4; 5; 6]). The speed of the triggering front, due to pore-pressure diffusion, depends on the distance from the fluid injection source (Equation (1)) and from the permeability \(k\) of the rock, embedded in \(D\) = \(Nk/\eta\), with other factors being the poro-elastic modulus, \(N\), and the pore-fluid dynamic viscosity, \(\eta\)[50]. On the other hand, earthquake migration rates of over 1 km/day (e.g., 0.1-1 km/h) are likely attributed to aseismic creep episodes (e.g., [52]). [65] have documented the case of a seismic swarm in Malamata, i.e., below station MALA (Figure 1), which exhibited a pattern of expanding seismicity at a rate of \(\sim\)125 m/day. However, it was manifested as a series of intermittent bursts, with seismicity migration speeds of 2-10 km/day over a short duration and distance. This example indicates how fluid-driven seismicity can be combined with short-lived aseismic slip episodes. We presented a long-range earthquake migration pattern, covering a \(\sim\)32 km distance from Nafpaktos to Aigion over the course of \(\sim\)15 months (Figure 6). Although this sequence evolved eastwards at an average speed of \(\sim\)70 m/day, it progressed in a series of bursts involving events of moderate magnitude that triggered their own sub-sequences. This pattern is consistent with pore-fluid diffusion, evidenced by an expanding triggering front of hydraulic diffusivity \(D\) = 2.2 m\({}^{2}\)/s through an active patch of 11-12 km, delimited by a back-front of seismicity deficit (Figure 6). A similar pattern has been observed in 2011 in Oichalia, South Peloponnese, where, likewise, a swarm evolved southwards in a series of episodes associated with major events of NNW-SSE-oriented normal faults, within an active patch following a parabolic triggering front [66]. In that case, the hydraulic diffusivity was \(D\) = 1.1 m\({}^{2}\)/s, the active fault patch was \(\sim\)8-km-long and it traveled a distance of \(\sim\)10 km over 160 days, i.e., at an average speed of 63 m/day. In addition, we estimated the mean squared distance (\(msd\)) of seismicity with time for the eastwards expanding seismic activity, enclosed within the active patch defined by the triggering- and back-fronts. The \(msd\) shows a step-like increase with time that can be approximated, overall, by a power-law function, with a diffusion exponent of \(a\) = 1.81 \(\pm\) 0.17 that indicates super-diffusion. [60] studied separately the distinct seismic clusters occurring in the spatial groups #4, #6 and #8 (e.g., Figures A1, A3 and A4 in Appendix A), yielding diffusion exponents lower than 0.2 and sub-diffusion. However, herein we observe that if the seismic clusters are jointly studied on a larger scale, a much faster diffusive process is obtained that spans from the Rion strait in the west to offshore Aigion in the east (Figure 4, top). In terms of the CTRW theory, the overall super-diffusive process resembles a Levy walk (e.g., [67]), with intermediate asymptotics having different exponents. High diffusion exponents, close to or greater than unity, are found in anomalous fluid transport processes in heterogeneous and fractured media [68].