On the origin of electrotelluric disturbances prior to an earthquake in Kalamata, Greece

A long distance (200 km) electromagnetic signal occured at Keratea (near Athens), few days prior to the September 13th 1986, Kalamata earthquake. We suggest an explanation based on the fact that long range stress occuring before an earthquake should create local electrical potential gradients in heterogeneous ground at great distances. This could be a general explanation for the origin of electrical telluric signals appearing before an...