AGU Fall Meeting, San Francisco CA, USA, 10-14 December, 2007
Maria Lancieri, Aldo Zollo
It has been shown that the initial portion of P- and S-wave signals can provide information about the final earthquake magnitude in a wide magnitude range. This observation opens the perspective for the real-time determination of earthquake source parameters.\\ In this paper we describe a probabilistic, evolutionary approach for the real time magnitude estimation which can have a potential use in earthquake early warning. The technique is based on empirical prediction laws correlating the low-frequency peak ground isplacement measured in a few seconds after the P and/or S phase arrival (PD) and the final event magnitude. The evidence for such a correlation has been found through the analyisis of 256 shallow crustal events in the magnitude range $M_{JMA}$ 4-7.1 located over the entire Japanese archipelago.\\ The PD measured in a 2-sec window from the first P-phase arrival correlates with magnitude in the range M 4-6.5. While a possible saturation effect above M 6.5 is observed, it is no more evident in an enlarged window of 4-sec. The scaling of S peaks with magnitude is instead observed also at smaller time lapses (i.e., 1-sec) after the first S-arrival.\\ We developed a technique to estimate the probability density function (PDF) of magnitude, at each time step after the event origin. The predicted magnitude value correspond to the maximum of PDF, while its uncertainty is given by the 95% confidence bound. The method has been applied to the 2007 ($M_{JMA}$ 6.9) Noto-Hanto and 1995 ($M_{JMA}$ 7.3) Kobe earthquakes.\\ Results of this study can be summarized as follow:\\ - The probabilistic algorithm based on predictive model based on PD vs final magnitude is able to provide fast and robust estimation of the final magnitude.\\ - The information available after few seconds from the first detection of P phase at the network is useful to predict the peak ground motion at a given regional target with uncertainties which are comparable to those derived from the attenuation law.\\ - The near-source, S-phase data can be used jointly with P data for regional early warning purposes, thus increasing the magnitude estimation accuracy and reliability.