Geoelectric field and seismicity changes preceding the 2018 Mw6.8 earthquake and the subsequent activity in Greece

A strong earthquake of magnitude Mw6.8 struck Western Greece on 25 October 2018 with epicenter at 37.515N 20.564E. It was preceded by an anomalous geolectric signal that was recorded on 2 October 2018 at a measuring station 70km away from the epicenter. Upon analyzing this signal in natural time, we find that it conforms to the conditions suggested (e.g., Entropy 19 (2017) 177) for its identification as precursory Seismic Electric Signal (SES) activity. Notably, the observed lead time of 23 days lies within the range of values that has been very recently identified (Entropy 20 (2018) 561) as being statistically significant for the precursory variations of the electric field of the Earth. Moreover, the analysis in natural time of the seismicity subsequent to the SES activity in the area candidate to suffer this strong earthquake reveals that the criticality conditions were obeyed early in the morning of 18 October 2018, i.e., almost a week before the strong earthquake occurrence, in agreement with earlier findings. Furthermore, upon employing the recent method of nowcasting earthquakes, which is based on natural time, we find an earthquake potential score around 80% just before the occurrence of this Mw6.8 earthquake. In the present version of this manuscript, we also report the recording of more recent SES activities.Comment: 11 pages including 13 figures. The major part of this paper appeared in Entropy 20 (2018) 882 by the first two author