A comparison of tc and tp for magnitude estimation in earthquake early warning

[1] We determined the tc and tp parameters from the K-NET strong motion records of 16 earthquakes in Japan with moment magnitude (Mw) ranging from 6.0 to 8.3. A 0.075 Hz high-pass Butterworth filter was applied for determination of tc based on our previous studies. It was found that different pole selections of the Butterworth filter lead to different uncertainty in magnitude determination. Our results show that using two poles in the filters results in the best magnitude estimates, i.e., minimized the standard deviation in magnitude determination in comparison to Mw using tc. The tp parameters (Allen and Kanamori, 2003) were also determined with the same dataset using the Wurman et al. (2007) procedure. It was found that tp values obtained from this dataset, and using the Wurman procedure, had a larger uncertainty. However, when a 0.075 Hz high-pass Butterworth filter with five poles was added, the uncertainty in tp-derived magnitude estimates decreased minimizing the standard deviation in magnitude determination using tp. This difference in the behavior of tc and tp can be used to further reduce the uncertainty in rapid magnitude determination for earthquake early warning. When the magnitude estimations from tc and tp of each event are averaged to provide a new magnitude estimate, the standard deviation in magnitude estimates is reduced further to 0.27 magnitude units. Citation: Shieh, J.-T., Y.-M. Wu, and R. M. Allen (2008), A comparison of tc and tp for magnitude estimation in earthquake early warning, Geophys. Res. Lett., 35, L20301, doi:10.1029/ 2008GL035611.