A Waveform Envelope-Based Reality Check Algorithm in Early Warning

Abstract:

Current earthquake early warning systems usually make magnitude and location predictions and send out a warning to the users based on those predictions. We describe an algorithm that assesses the validity of the predictions in real time. Our algorithm monitors the envelopes of horizontal and vertical acceleration, velocity, and displacement. We compare the observed envelopes with the ones predicted by Cua & Heaton’s envelope ground motion prediction equations. We define a “test function” as the logarithm of the ratio between observed and predicted envelopes at every second in real time. Once the envelopes deviate beyond an acceptable threshold, we declare a misfit. Kurtosis and skewness of a time evolving test function are used to rapidly identify a misfit. Real-time kurtosis and skewness calculations are also inputs to a Linear Discriminant Analysis that ultimately decides if there is an unacceptable level of misfit. This algorithm is designed to work at a wide range of amplitude scales; it works for both small and large events.