PRELIMINARY FOCAL MECHANISM SOLUTIONS

Research Group: Kiratzi A., Roumelioti Z., Benetatos C. and A. Karamitrou

The Department of Geophysics of the Aristotle University of Thessaloniki (DG-AUTH) determines moment tensors shortly after the occurrence of a strong event in Greece and the surrounding lands. It disseminates these solutions to a) the European Mediterranean Seismological Centre (EMSC) since October 2005 and b) the WEB page of the Seismological Station of DG-AUTH since May 2006.

The solutions are NOT automatic yet. We currently test the automatic computation of moment tensors but at the moment all solutions are manually checked by a member of the team. The applied method includes a three-component complete waveform inversion using broad band data from Aristotle University of Thessaloniki (HT), Patras University (PSLNET) and National Observatory of Athens (NOA) seismic networks, as well as from other European Networks (e.g. GEOFON and MEDNET).

The method followed for the Moment Tensor retrieval is described in Dreger (2003) and in a number of our group's publications, that can be found here.
The Green's functions are calculated using the FKRPROG code (Saikia, 1994).

Solution Quality: Each Moment Tensor solution is assigned a quality value based on the overall variance reduction (VR, goodness of fit between observed and synthetic waveforms) and the number of stations used in the inversion. The criteria for choosing the appropriate quality value are the following:

  • Quality A: Is assigned to the best solutions, i.e. with VR>80% and at least three (3) stations contributing to the solution
  • Quality B: VR=70%-80% or VR>80% but with 1 or 2 stations contributing to the solution
  • Quality C: VR=60%-70%
    Solutions with VR<60% are not considered reliable and thus are not distributed.

    For additional publications regarding the Moment Tensor Inversion method you can follow this link to Berkeley Seismo Lab.

    References

    Dreger, D. S., 2003, TDMT_INV: Time Domain Seismic Moment Tensor INVersion, International Handbook of Earthquake and Engineering Seismology, Volume 81B, p 1627.

    Saikia, C., 1994. Modified frequency–wave number algorithm for regional seismo-grams using Filon’s quadrature; modelling of Lg waves in eastern North America. Geophys. J. Int. 118, 142–158.

     

    ATTENTION! Moment Tensor solutions listed in these electronic pages are fast (semi-automatic) and may contain errors. We are currently reviewing all of our fast solutions and we will soon publish the final results. For further information regarding the computation method and our preliminary results please refer to the following report to EMSC:
    Roumelioti, Z., Ch. Benetatos, A. Kiratzi and D. Dreger (2007). Near-real time moment tensors for earthquakes in Greece provided by the Dept of Geophysics, Aristotle University of Thessaloniki (AUTH-solutions), Report submitted to the European Mediterranean Seismological Center (EMSC), http://emsc-csem.org. (pdf file)