A rapid response magnitude scale for timely assessment of the high frequency seismic radiation

In this work the scaling of seismic moment (M0) and radiated energy (Er) is investigated for almost 800 earthquakes of the 2016-17 Amatrice-Norcia sequences in Italy, ranging in moment magnitude (Mw) from 2.5 to 6.5. The analysis of the M0-to-Er scaling highlights a breaking of the source self-similarity, with higher stress drops for larger events. Our results show the limitation of using M0, and in turn Mw, to capture the variability of the high frequency ground motion. Since the observed seismicity does not agree with the assumptions on stress drop in the definition of Mw, we exploit the availability of both Er and M0 to modify the definition of Mw and introduce a rapid response magnitude (Mr), which accounts for the dynamic properties of rupture. The new Mr scale allows us to improve the prediction of the earthquake shaking potential, as shown by the reduction of the between-event residuals computed for the peak ground velocity. The procedure we propose is therefore a significant step towards a quick assessment of earthquakes damage potential and timely implementation of emergency plans.