Seismic and electrical precursors to the 17-1-1983, M7 kefallinia earthquake,Greece: Signatures of a SOC system

Prior to the 17-1-1983 event, the seismicity of the broader area of the Ionian islands and western Greece exhibited several phenomena interpretable in the context of a self-organised critical system with long range interactions. The regional seismic energy release exhibited power law acceleration towards the time of rupture, the numerical modelling of which yields a time-to-failure of 1983.1 ± 0.2. Time dependent changes were also observed in the b-values, assuming the form of monotonic increase that promptly reversed after the earthquake. This indicates the induction of instability to the region due to the earthquake preparation process, which is consistent with the critical point earthquake model. The critical point model predicts that failure is a co-operative effect occurring at small scale, and cascading from the microscopic to the macroscopic scale. This involves a crack propagation avalanche at the terminal phase of the seismic cycle, the time function of which has been modelled with a limited class of characteristic transient bay-like shapes, featuring a corner frequency and inverse power energy distribution law. Electrification processes due to crack propagation may generate an electrical precursor with similar characteristics. Such a potential precursor has been observed independently on 15-1-1983, approx. 120km from the epicentre. In consequence of our observations, we discuss a model relating seismicity and electrical precursors.