Research On The Calculation Method Of P-wave Magnitude For Early Warning From Frequency Analysis

According to the literature records,we learned three points:the concept of earthquake early warning,the present situation of earthquake early warning systems and the calculation methods of early warning magnitude.By studying the results of previous studies,the warning time window was determined to be 3 seconds.We selected 12 4-7 magnitude earthquakes in China as the original data,and studied their frequency spectrum and fitted the magnitude formulas.The results of the narrow band filters showed that the low frequency section of the near field P wave acceleration records were more stable,especially the frequency band below 2Hz.Combined with the traditional magnitude formula,the P wave amplitude values of low frequency sections were used to fit the magnitude calculation formula Mn for the near field,then it was applied to 13 cases in Japan which are selected from K-net and the error of the first report was 0.25.By comparing the Pd magnitude calculation mathods,which error was 1.12,it showed that our results were more stable and reliable in the earthquake early warning.In order to testing and verifying the results of the first report,we estimated the S wave arriving time through epicenter and studied the frequency spectrum distribution,then,we found that the frequency characteristics of the S wave were similar to the P wave.The frequency band below 2Hz is more stable and suitable for fitting the magnitude formula Ms.We applied Ms to calculate the Japanese earthquake examples and found that,Ms were very close to Mn,which error was about 0.5,and closer to Mw,so it can serve as a strong circumstantial evidence for the first report.So,the methods of magnitude determination in this paper is more suitable for the calculation of the magnitude of the near field in earthquake early warning and the result is more reliable.