Real-time magnitude proxies for earthquake early warning in Israel

In quest for robust real-time magnitude proxies for earthquake early warning (EEW) in Israel, we use off-line data from 95 earthquakes of magnitudes 2.5-5.3 that were recorded by 25 stations of the Israel Seismic Network between 2003 and 2011. We first examine correlations between the catalogue magnitudes and five different attributes of the early part of the P phase, including the low-pass-filtered peak displacement, the peak velocity, the integral of the velocity squared, the predominant period and the characteristic period. We then establish site-specific empirical relations between each proxy and the catalogue magnitude, and infer similar relations for the entire network, after disregarding data recorded at stations for which the site-specific correlation is poor. We find that amplitude-based magnitude proxies are more suitable than frequency-based proxies for rapid magnitude determination, and show that use of site-specific empirical relations between amplitude-based magnitude proxies and catalogue magnitude can increase the accuracy of real-time magnitude estimations. While the present study utilizes off-line data of limited magnitude range, its results clearly indicate that rapid earthquake magnitude determination in Israel and adjacent areas is feasible and can be incorporated effectively into an EEW algorithm.