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A crucial part of proposed earthquake early warning systems is a rapid estimate for earthquake magnitude.Most of these methods are focused on the first part of the P-wave train,the earlier and less destructive part of the ground motion that follows an earthquake.A method has been proposed by using the period of the P-wave to determine the magnitude of a large earthquake at local distance,and a specific relation for the Sichuan region was calibrated according to acceleration records of Wenchuan earthquake.The Mw 6.6 earthquake hit Lushan County,Sichuan,on April 20,2013 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks connected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms.A discrepancy between the local magnitude(ML)estimated by means ofτc evaluation and the standard ML(6.4 vs.7.0)suggests using caution when ML vs.τc calibrations do not include a relevant dataset of large earthquakes.Effects from large residuals could be mitigated or removed by introducing selection rules onτc function,by regionalizing the ML vs.τc function in the presence of significant tectonic or geological heterogeneity,and by using probabilistic and evolutionary methods.
A crucial part of proposed earthquake early warning systems is a rapid estimate for earthquake magnitude. Host of these methods are focused on the first part of the P-wave train, the earlier and less destructive part of the ground motion that follows an earthquake. A method has been proposed by using the period of the P-wave to determine the magnitude of a large earthquake at local distance, and a specific relation for the Sichuan region was calibrated according to acceleration records of Wenchuan earthquake. Mw 6.6 earthquake hit Lushan County , Sichuan, on April 20, 2013 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks connected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms. A discrepancy between the local magnitude (ML) estimated by means of τc evaluation and the standard ML (6.4 vs.7.0) suggests using caution when ML vs. τc calibrations do not include a relevant dataset of large earthq uakes. Effects from large residuals could be mitigated or removed by introducing selection rules on τc function, by regionalizing the ML vs. τc function in the presence of significant tectonic or geological heterogeneity, and by using probabilistic and evolutionary methods.