Studies on the source mechanism and SES for 28 earthquakes in Greece

Abstract

The VAN telemetric network used to forecast earthquakes in Greece has been in operation since January 1983. Eighteen VAN stations were established in various locations within Greece to detect Seismic Electric Signals (SES) which are thought to precede the onset of earthquakes. During the past thirteen years, success in predicting the three main parameters (the epicenter, time, and magnitude) of impending large magnitude (mb> 5.0) earthquakes has been remarkable. Two VAN stations, Ioannina (IOA) and Pyrgos (PIR), which have been in operation since 1983 and cover overlapping seismic areas, detected SES before the onset of 25 out of 28 different but spatially grouped earthquakes. Among the 25 predicted earthquakes, 15 were preceded by SES at IOA station and IO were preceded by SES at PIR station. Because this study focuses on SES at the IOA station only, SES detected at the PIR station were not analyzed. Source mechanisms for the 28 earthquakes predicted from SES at the IOA and PIR stations are analyzed for their relationship to the SES as well as the location of these two SES stations. Other stations have not been included because they cover different areas and the data currently available from them are not abundant enough to draw any significant conclusions. A comparison of the 28 earthquakes reveals that all earthquakes with reverse mechanisms were preceded by SES at the IOA station. The parameters (i.e., polarity, magnitude, time lag, and duration) for these SES are, however, dissimilar. All normal or strike slip earthquakes west of Kefallinia Island were predicted by SES at the PIR station. South of the PIR station, all earthquakes with focal mechanism parameters similar to the earthquakes west of Kefallinia Island were also preceded by SES at the PIR station. Hence, different earthquakes with similar mechanisms were preceded by SES with different polarities and vice versa, the polarity of the SES does not seem to be affected by the earthquake's mechanism. The polarity distribution suggests a possible correlation with tectonic zones in Greece. There is also clearly a correlation between type of focal mechanism, location of the earthquake and the station at which SES preceded the event.