Designing small-aperture seismic arrays to enhance earthquake monitoring on ocean islands: Application to Antikythera island, Greece

We present an optimisation strategy in order to design a seismic array at the Antikythera island (Greece), consisted of nine elements in total, namely, eight new and one permanent station. This new seismic array aims to improve the seismic event detection capability and location accuracy of the Hellenic Unified Seismic Network (HUSN) at the SW-end of Greece, for local and regional seismicity, which is constrained by the sparse station coverage between Peloponnese and Crete. Instead of simply being based on theoretical transfer function calculations, we set up a synthetic dataset of realistic seismic sources and we determine the backazimuth and slowness vectors based on array beamforming via a global optimisation scheme that takes into account several criteria, such as amplitude power, event mislocation, array shape and landscape restrictions. The result is a set of station coordinates whose positions shape different array configurations at each step of the optimisation process, affecting both the maximum amplitude beam of P and S wavefields, as well as the ability of each array configuration to successfully resolve the backazimuth of each seismic source. The optimal array is determined as the one associated with the minimum score of an objective function based on the above criteria, being an irregular shaped array with an aperture of ~4.0 km.