τ_p^max magnitude estimation, the case of the April 6, p 2009 L’Aquila Earthquake

Abstract

Rapid magnitude estimate procedures represent a crucial part of proposed Earthquake Early Warning Systems. Most of these estimates are fo- cused on the first part of the P-wave train, the earlier and less destructive part of the ground motion that follows an earthquake. Allen and Kanamori [2003] proposed to use the predominant period of the P-wave to determine the magnitude of a large earthquake at local distance and Olivieri et al. [2008] calibrated a specific relation for the Italian region. The Mw 6.3 earthquake that hit Central Italy on April 6, 2009 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks con- nected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms. A large discrepancy between ML estimated by means of τ max evaluation and standard ML (6.8 ± 1.5 vs. 5.9 ± 0.4) suggests using p caution when ML vs. τmax calibrations do not include a relevant dataset of p large earthquakes. Effects from large residuals could be mitigated or removed introducing selection rules on τ function, by regionalizing the ML vs. τmax pp function in the presence of significant tectonic or geological heterogeneity, and using probabilistic and evolutionary methods.