Evidence of shear-wave splitting in the eastern Corinthian Gulf (Greece)

Abstract

The analysis of local earthquakes recorded by the Cornet network and located in the Gulf of Corinth (Greece) has revealed the existence of shear-wave splitting. The visual inspection technique is used to estimate the polarization direction of the fast shear wave and the time delay between the two split shear waves. The selected earthquakes are located close to one of the Cornet stations. Most of these earthquakes are recorded by only one station and their azimuth and angle of incidence are estimated using the covariance matrix decomposition method combined with the P-wave polarization direction. Polarigrams plotted for the horizontal components present a clear linear and almost constant polarization for each station, independent of the azimuth of the earthquake, except for one station where different S fast polarization directions are observed. The mean direction of the fast shear wave polarization at Paradeisi station is 146°N, at Sofiko station 104°N and at Villia station 142°N. At Desfina station, two different main S fast polarization directions were observed, one 143°N and the other 55°N. The calculated time delays between the two split shear waves are higher for the stations located in the eastern part of the Gulf. Comparing the mean S fast polarization direction with the direction of local faulting, we observe that they are approximately parallel at Sofiko station, while at Villia station they are almost perpendicular. In general, the obtained mean S fast polarization directions at the Cornet stations are perpendicular to the direction of the extension of the Gulf which is NNE–SSW and consistent with the extensive dilatancy anisotropy (EDA) model.