Waveform Relocation and Focal Mechanism Analysis of an Earthquake Swarm in Trichonis Lake, Western Greece

Abstract

Abstract In early April 2007, a series of moderate earthquakes (M L 4.1–4.8) oc-curred in the area of Trichonis Lake in western Greece. The earthquake activity waswell recorded by the Hellenic Broadband Seismic Network ( HL ) operated by the Na-tional Observatory of Athens. Initial locations for 156 events of the swarm showed adiffuse image of seismicity. Subsequently, 101 events are precisely relocated, calcu-lating source-specific station terms and differential travel times from waveform crosscorrelation. Uncertainties in relocations are estimated with a bootstrap approach byrandomly weighting the original picks and the differential times. Additionally, wave-forms of seven out of the eight largest earthquakes of the swarm were inverted inorder to derive regional moment tensor solutions. The results showed a tight north-northwest–south-southeast cluster located on an offshore extension of a similarlyoriented fault trace mapped onshore. Moment tensor solutions indicate normal fault-ing with a substantial component of left-lateral strike-slip motion. It is possible thatthis identified fault forms part of a link that connects the Gulf of Corinth rift system tothe west-northwest–east-southeast fault zone south of Trichonis basin.Online Material: Event catalog and focal mechanism for the eight largest events.Introduction