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 (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 M₀-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 M₀, 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 M₀ 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.