Support vector evaluation of the unpredictability of the electrotelluric field variations signal before major earthquakes

Observations of electrotelluric field (ETF) variations (long-term geoelectric potential difference) were conducted for a five year period (1993-97), in western Greece. During this time interval, 18 large earthquakes, M>4.8, took place in the vicinity of Patras, within 150 km of the VAN station. This work investigates the nonlinear predictability of the ETF signal. Support vector machines trained on a signal window have been used to predict the next sample. We observe a significant increase at this short-term unpredictability of the ETF signal at about 2 weeks before many major earthquakes. This fact can be attributed to a quick time variation of the dynamics that produce the ETF signal due to the earthquake generation process. This unpredictability increase can be taken advantage of for signaling an increased possibility of a large earthquake within the next few days.