LOCAL MAGNITUDE CONVERSION TO UNIFIED MOMENT MAGNITUDE IN THE CROATIAN EARTHQUAKE CATALOGUE (CEC)

Abstract: The earthquake catalogue of events that occurred in Croatia (Croatian Earthquake Catalogue - CEC) during the period 373BC-2015 was compiled for achieving homogeneity for magnitudes. The need to use moment magnitudes in hazard analyses (since the moment magnitude characterizes the earthquake size accurately and the selected ground motion prediction equations (GMPEs) employ the moment magnitude (MW) scale) motivated this work. Using MW magnitude values obtained by the centroid moment tensor solutions (Harvard GCMT catalog, PDE catalogue) and from RCMT solution (INGV), magnitude conversion equation for local magnitudes (which are reported in CEC for each event) was derived using errors-in-variables regression (EIVREG), a least squares data modeling technique in which observational errors on both dependent and independent variables are taken into account. About 120 GCMT/RCMT solutions for small-to-large events, varying MW from 3.5 to 5.7, were used to derive the local relationship converting the ML to MW. The completeness and homogeneity of the unified catalogue were also analyzed, as well as a and b value of the Gutenberg-Richter frequency-magnitude relation. A prepared unified homogeneous catalogue can serve as a reference catalogue for seismic hazard estimates and other seismic studies in Croatia and neighbouring areas.

Keywords: Earthquake catalogue, local magnitude, moment magnitude, errors-in-variables, seismicity.