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Abstract

Seismic swarms frequently exhibit spatial migration of event hypocenters with time attributed to external aseismic stresses, such as pore-fluid pressure diffusion, aseismic creep, or magmatic intrusion, that may act as the driving mechanism. Earthquake diffusion, observed in such cases, can be highly anisotropic, occurring preferentially along fractures and zones of weakness over wide spatial and temporal scales. The efficient modelling of the complex spatiotemporal evolution of seismic swarms, hence, represents a major challenge. Herein, we develop a stochastic model, based on the Continuous Time Random Walk (CTRW) theory, to map the spatiotemporal evolution of seismic swarms. Within this context, we describe the spatiotemporal evolution of seismicity with an appropriate master equation and the time-fractional diffusion equation (FDE). The applicability of the model is demonstrated in two seismic swarms associated with pore-fluid pressure diffusion, the 2001 Agios Ioannis (Corinth Rift) and the 2014 Long Valley Caldera (California) swarms. The analysis shows anomalous earthquake diffusion, with diffusion exponents less than unity in both cases, as well as broad waiting-times distributions with asymptotic power-law behavior. Such properties are intrinsic characteristics of a sub-diffusive process. Furthermore, the asymptotic solution of the FDE can successfully capture the main features of earthquake progression in time and space. Overall, the results demonstrate that the CTRW model can efficiently be used to map earthquake diffusion in seismic swarms. AcknowledgementsThe research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 00256).