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

A possible correlation between SES (seismic electric signals of the VAN met hod) characteristics and earthquake parameters is investigated for the peri od January 1, 1983-December 31, 1994 for western Greece. During this period , there were total of 55 earthquakes of m(b) greater than or equal to 5.0 i n the region of the so-called selectivity maps of the Ioannina (IOA) and Pi rgos (PIR) VAN stations. CMT solutions are available for 29 of these earthq uakes; 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 direct ion was not unique. (3) Eleven earthquakes in the zone west of Kefallinia t o Peloponese preceded by SES at PIR were of the strike-slip type with varyi ng degrees of normal component. The vector direction of SES at PIR for thes e earthquakes was predominantly westward. (4) The source mechanism changed from largely strike-slip type to thrust type in the above zone at the end o f 1987, and this coincided with a shift in the sensitive site from PIR to I OA, indicating a possible correlation between the source mechanism and sele ctivity characteristics of VAN stations. (C) 1999 Elsevier Science B.V. All rights reserved.