Waveform relocation and focal mechanism analysis of an earthquake swarm in Trichonis Lake, western Greece

In early April 2007, a series of moderate earthquakes (M-L 4.1-4.8) occurred in the area of Trichonis Lake in western Greece. The earthquake activity was well recorded by the Hellenic Broadband Seismic Network (HL) operated by the National Observatory of Athens. Initial locations for 156 events of the swarm showed a diffuse image of seismicity. Subsequently, 101 events are precisely relocated, calculating source-specific station terms and differential travel times from waveform cross correlation. Uncertainties in relocations are estimated with a bootstrap approach by randomly weighting the original picks and the differential times. Additionally, waveforms of seven out of the eight largest earthquakes of the swarm were inverted in order to derive regional moment tensor solutions. The results showed a tight north-northwest -south-southeast cluster located on an offshore extension of a similarly oriented fault trace mapped onshore. Moment tensor solutions indicate normal faulting with a substantial component of left-lateral strike-slip motion. It is possible that this identified fault forms part of a link that connects the Gulf of Corinth rift system to the west-northwest-east-southeast fault zone south of Trichonis basin.