An Evolutionary Shaking‐Forecast‐Based Earthquake Early Warning Method

Abstract

AbstractHere we propose a methodology for Earthquake Early Warning (EEW) able to issue the alert based on the real‐time estimation of the epicentral area where a peak ground Intensity measure is expected to exceed a user‐set ground shaking level. The method provides in output a P‐wave‐based, time‐evolutive “early” shake map. It combines the peak ground velocity predictions available from the observed P‐wave amplitudes and from the region‐specific ground motion prediction equation, using progressively updated estimates of earthquake location and magnitude. The P‐wave displacement, velocity and acceleration amplitudes are jointly measured on a progressively expanded P‐wave time window while the earthquake location and magnitude are evaluated using the first P‐arrival time and displacement amplitudes at near source stations. A retrospective analysis of the 2016, Mw 6.5 Central Italy earthquake records shows that depending on the network density and spatial source coverage, the method naturally accounts for effects related to the earthquake rupture directivity and spatial variability of strong ground motion related to crustal wave propagation and site amplification. Within 1.5 s from the first alert (5.15 s after the origin time), the simulated performance of the system in predicting the event ground shaking is very high: in the 40 km‐radius area that suffered an Intensity MCS VIII–IX, 41 over 42 strong‐motion instrumented sites would have been successfully alerted, with only one false alarm. Even considering the calculated blind‐zone of 15 km radius, a 15–55 km wide annular area would have received the alert 2–14.5 s before the occurrence of the strong ground shaking. The proposed EEW method evolves with time in a way that it minimizes the missed alarms while increasing successful alarms and to a lesser extent false alarms, so it is necessary for the end‐user to accept these possibilities and account for them in a probabilistic decision scheme depending on the specific safety actuation measure to be undertaken in real‐time.