Directional properties of VAN's SES and ULF MT signals at Ioannina, Greece

Abstract

In order to examine the validity of the earthquake prediction technique developed in Greece by VAN (Varotsos, Alexopoulos and Nomicos) and elucidate the underlying physical processes, we performed a magnetotelluric (MT) recording of the ULF band (3–200 s) in the vicinity of VAN's sensitive station, Ioannina (IOA). By comparing MT electric field of ionospheric or magnetospheric origin, electric field of lightning origin and VAN's seismic electric signals (SES), the following facts were revealed. (1) The MT electric field always varies in the ENE–WSW direction, indicating existence of significant electrical conductivity contrast near the site. (2) The lightning electric field orientation is somewhat more scattered but still holds the same preferred direction as that of the MT electric field. The scatter is larger for larger lightning field, probably due to closer location of lightning stroke to the station and/or due to no-linear saturation of the recording signals. (3) The SES electric field orientation is even more scattered than that of the lightning origin. These observations suggest that the sources of the SES are in the neighborhood of the station. It is still unclear how the SES, associated with distant earthquakes, are emitted from the sources near the IOA station.