Local Magnitude (ML) Calibration for Georgia

Modernization of national Seismic Network of Georgia started from 2003. At this moment National Seismic Network of Georgia (Operated by Institute of Earth Science and National Seismic Monitoring center,Ilia state university) consists from 25 stations. Since 2003 IES/NSMC to estimate magnitude of the earthquakes instead of Soviet K class started using ML scale. In this study we derived attenuation function and corresponding station adjustments for the local magnitude calculations in Georgia. Standard distance correction terms may have a significant bias with distance if applied in a region with different attenuation properties, resulting in an incorrect magnitude. For the calculations, we used events with magnitude M>3.0. Also the data from the stations in north-eastern part of turkey, operated by AFAD and Kandili Observatory were used as well. The local magnitude scale was computed by regression analysis of the maximum shear wave trace amplitudes measured on horizontal synthesized Wood-Anderson seismograms for each station. New local magnitude formula have been used to automatically recalculate ML for all local events in the seismic database of Institute of earth science and National seismic monitoring center. We compare the resulting magnitudes to previous values. Our results show the importance of correct calibration of the distance correction terms for accurate local magnitude assessment in regional networks.