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.