Method of accurate-fast magnitude estimation for earthquake early warning -----Trial and application for the 2008 Wenchuan earthquake

Abstract

Earthquake early warning (EEW) system is one of the most useful tools to mitigate seismic hazards. Although EEW approaches have already been developed worldwide, the issues of improving the accuracy and applicability were still controversial. On the basis of the existing measurable parameters related to the earthquake magnitude, we proposed a method in terms of the squared integral displacement (ID2) to anticipate the magnitude in real-time for EEW purpose that can be used for large earthquakes. With the main-shock and aftershocks of the 2008 Ms 8.0 Wenchuan earthquake, we investigated the regression relationships between the proposed ID2 and earthquake magnitude, based on which the magnitude predication formula was derived. Then the predicated accuracy from ID2 was compared with that from τc and Pd. By comparing the differences between the estimated and reported magnitudes, the proposed ID2 method was of the highest accuracy among the investigated 3 parameters. Next we analysed the ground motion characteristics in the frequency domain and established the correlations between the Fourier amplitude and spectral intensity of the initial P wave with the magnitude estimation differences, based on which a revision method of reducing such differences was put forward and the saturation effects of predicting large magnitudes were well mitigated simultaneously.