New frequency-based real-time magnitude proxy for earthquake early warning

Abstract

The two frequency-based magnitude proxies currently employed by earthquake early warning systems in California are the predominant and the characteristic periods. These proxies, obtained using simple expressions that are valid for noise-free monochromatic signals, yield erroneous result. The log-average period, τ log, introduced in this study, is calculated directly from the actual velocity spectrum of the first few seconds of the seismic record. Using data from South California and Japan consisting of 440 earthquakes whose magnitudes range between 3 and 7.3, it is demonstrated that τ log is better correlated with the catalog magnitude than the predominant period and provides better magnitude assessment than the characteristic period for small magnitudes (M<4). The average prediction error is reduced with increasing the input interval up to 6 s. It appears that a single linear scaling describes the relation between log(τ log) and the catalog magnitude for the entire magnitude range studied here. Key PointsThe log-average period is better correlated with magnitude than other proxiesThe log-average period provides better magnitude prediction than other proxiesThe real-time log-average period is expected to enhance the performances of EEWS