Influence of the noise fluctuactions in the estimate of duration-Magnitude. E. Del Pezzo*, F. Bianco and G. Saccorotti INGV - Osservatorio Vesuviano. Via Diocleziano, 328 80124 Naples, Italy * delpezzo@ov.ingv.it Introduction The aim of this report is to quantify the error related to the estimate of the Duration-Magnitude, due to the seismic noise fluctuations. We will carry on an example on data from Mt. Vesuvius. The report is divided into the following three sections: 1. rms noise distribution. We find that the statistical distribution which best represent the experimental data is the log-normal one, and calculate the best fit parameters. 2. Experimental distribution of earthquake-durations. The function which describes the time- envelope of the seismograms at Mt. Vesuvius is well known from a study of the seismic attenuation in the area (Bianco et al. 1999). As the earthquake duration is defined as the time point at which the envelope encounters the rms-noise level, we can numerically estimate the corresponding distribution of the earthquake durations for each given Magnitude. 3. Errors associated to the duration-Magnitude. Finally, we deduced the errors associated to the duration- Magnitude from the corresponding distribution of the earthquake durations. All calculations are active in the present MATHCAD worksheet, which can be easily adapted for applications different from the present example rms noise distribution The present section describes the procedures used to deduce the properties of the rms-noise distribution. First we select OVO station of the seismic network - see the Open File Report by Buonocunto et al. 2001, on line at www.ov.ingv.it -. The duration Magnitude scale was calibrated (Del Pezzo and Petrosino, 2001 and references therein) for this station which was set up since 1972 with modern sensors, and was mantained in the same configuration up to the present time. It is the reference station for the calculation of the earthquake duration Magnitude at Mt. Vesuvius. a2000 D:\..\Rmsout00.txt := a1999 D:\..\Rmsout99.txt := a1998 D:\..\Rmsout98.txt := a1997 D:\..\Rmsout97.txt := RMS stack a2000 a1999 , a1998 , a1997 , ( ) := The input files containing the rms values calculated in the pre-event 10 seconds for each local earthquake recorded at OVO from 1997 to the end of 2000. RMS is the vector containing the stack of all the pre-event rms values