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

In this work the scaling of seismic moment (M(0)) and radiated energy (E(r)) is investigated for almost 800 earthquakes of the 2016–17 Amatrice-Norcia sequences in Italy, ranging in moment magnitude (M(w)) from 2.5 to 6.5. The analysis of the M(0)-to-E(r) scaling highlights a breaking of the source self-similarity, with higher stress drops for larger events. Our results show the limitation of using M(0), and in turn M(w), 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 M(w), we exploit the availability of both E(r) and M(0) to modify the definition of M(w) and introduce a rapid response magnitude (M(r)), which accounts for the dynamic properties of rupture. The new M(r) 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.