A Study of P Wave Method for Earthquake Early Warning

Earthquake early warning (EEW) is to estimate the magnitude or intensity as well as the location of an event with the information of first several seconds of P wave, and to provide a warning for regions where damages are likely to occur. This thesis is separated to 2 parts to test EEW methods using P wave information. The purpose is to provide a quick and accurate method for practical EEW system. The first part of this study compares (average ground motion period) and (dominant ground motion period) methods, and emphasizes on the filtering process. K-net strong motion records in Japan were used, and 16 events with magnitude 6 to 8.3 were chosen to be analyzed. A 0.075 Hz high-pass Butterworth filter was applied for determination of based on our previous studies (Wu and Kananmori, 2005a, 2005b, 2008a, 2008b; Wu et al., 2006; 2007), and the results show that using two poles in the filters has the best magnitude estimates. On the other hand, was determined using Wurman et al. (2007) procedure, and the magnitude estimation was found to have large uncertainty. However, adding a 0.075 HZ high-pass Butterworth filter the same as procedure with five poles could obviously reduce the uncertainty. In addition, the best results of the two methods could be averaged to provide more accurate magnitude estimates. In the second part of this study, records from a strong motion array sensor system which installs at a building of Fire Fighting Bureau of Taitung county were selected to examine the and Pd methods. From 1996 to 2006, only Mw 6.1 Taitung earthquake with epicentral distance 14.5 km caused damage to this building. This fact provides this study to compare the difference between destructive and non-destructive events. According to the results, the method doesn’t provide good magnitude estimation in this case probably because of the low signal to noise ratio (SNR). On the other hand, only Pd of the destructive Taitung earthquake exceeds 0.5 cm which conforms to the results proposed by Wu and Kanamori (2005b, 2008). This result shows that in this case, it is better to warn a destructive event with a Pd threshold. In addition, it is also found that by this way to provide EEW, the location for the installment of seismometers doesn’t make obvious difference.