On the estimate of earthquake magnitude at a local seismic network

We investigated possible uncertainties and biases of magnitude estimate arising from instrument characteristics, site conditions and routine data processing at a local seismic network running in Southeastern Sicily. Differences in instrument characteristics turned out to be of minor importance for small and moderate earthquakes. Magnitudes routinely calculated with the HYPOELLIPSE program are obtained from the peak ground velocities applying a correction for the dominant period. This procedure yields slightly lower values than the standard procedure, where magnitudes are estimated from peak ground displacement. In order to provide the operators in the data center with a tool for an immediate estimate of earthquake size from drum records we carried out a bivariate regression relating local magnitude (M L ) to the duration of the signal and the travel time difference of P- and S-waves.