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摘要
A new seismic early warning algorithm is presented that estimates a magnitude threshold using the first 3 s of the P-wave coda on the vertical component. The algorithm considerably reduces the processing time compared to previous algorithms used by the Mexican seismic early warning system (Seismic Alert System of Mexico [SASMEX]). It was designed to alert earthquakes within the subducted Cocos plate. The t(p) + 3 algorithm was based on a training dataset of 76 accelerograms of 25 Mexican in-slab earthquakes, with focal depths > 40 km The algorithm uses two parameters based on the unfiltered vertical component of the P waves: the sum of the cumulative quadratic acceleration, a(nu(T)) and theta(p) a parameter that represents the slope of the cumulative acceleration. The model is based on a learning machine that linearizes piecewise the empirical relation between these two parameters and magnitude M-w. The resulting algorithm was tested on nine earthquakes that took place from 2014 to 2017, recorded in 37 strong-motion records. In addition, the algorithm was evaluated in the context of the Mexican earthquake early warning, applying it to 24 in-slab earthquakes occurring from 1995 to 2017 (5.0 < M-w < 7.1). The magnitude of 19 earthquakes was properly estimated; for four of them, it was overestimated and in one case the magnitude was underestimated. Three earthquakes M-w > 6.5 that affected Mexico City were included in the dataset: the M-w 6.5 event on 11 December 2011 and the destructive in-slab Tehuacan and Morelos earthquakes on 15 June 1999 (M-w 7.0) and 19 September 2017 (M-w 7.1). The retrospective application of the t(p) + 3 algorithm shows that these three earthquakes are correctly identified as M-w > 6 and would activate a seismic alert. The t(p) + 3 algorithm would have given an advance warning of 34, 35, and 16 s respectively, before the arrival of strong motion in Mexico City.
- 出版日期2018-8
