Local magnitude estimate at Mt. Etna

In order to verify the duration magnitude MD we calculated local magnitude ML values of 288 earthquakes occurring
from October 2002 to April 2003 at Mt. Etna. The analysis was computed at three digital stations of the
permanent seismic network of Istituto Nazionale di Geofisica e Vulcanologia of Catania, using the relationship
ML = logA+alog?-b, where A is maximum half-amplitude of the horizontal component of the seismic recording
measured in mm and the term «+alog?-b» takes the place of the term «-logA0» of Richter relationship. In
particular, a = 0.15 for ?<200 km, b=0.16 for ?<200 km. Duration magnitude MD values, moment magnitude
MW values and other local magnitude values were compared. Differences between ML and MD were obtained for
the strong seismic swarms occurring on October 27, during the onset of 2002-2003 Mt. Etna eruption, characterized
by a high earthquake rate, with very strong events (seismogram results clipped in amplitude on drum
recorder trace) and high level of volcanic tremor, which not permit us to estimate the duration of the earthquakes
correctly. ML and MD relationships were related and therefore a new relationship for MD is proposed. Cumulative
strain release calculated after the eruption using ML values is about 1.75E+06 J1/2 higher than the one calculated
using MD values.