Some relationship between VAN seismic electric signals (SES) and earthquake parameters

Abstract

A possible correlation between SES (seismic electric signals of the VAN method) characteristics and earthquake parameters is investigated for the period January 1, 1983–December 31, 1994 for western Greece. During this period, there were total of 55 earthquakes of m b≥5.0 in the region of the so-called selectivity maps of the Ioannina (IOA) and Pirgos (PIR) VAN stations. CMT solutions are available for 29 of these earthquakes; eighteen were preceded by SES at IOA and eleven at PIR. None of them was preceded by simultaneous SES at both stations. The main results are as follows. (1) The direction of the SES vector at IOA is correlated with the focal position of predicted earthquakes, although nearby earthquakes often have SES with dissimilar vector directions. (2) The SES of all nine thrust events of the 29 earthquakes were observed at IOA, but their vector direction was not unique. (3) Eleven earthquakes in the zone west of Kefallinia to Peloponese preceded by SES at PIR were of the strike-slip type with varying degrees of normal component. The vector direction of SES at PIR for these earthquakes was predominantly westward. (4) The source mechanism changed from largely strike-slip type to thrust type in the above zone at the end of 1987, and this coincided with a shift in the sensitive site from PIR to IOA, indicating a possible correlation between the source mechanism and selectivity characteristics of VAN stations.