Abstract:As an effective means of reducing casualties and economic losses, earthquake early warning systems have received considerable attention and many have been implemented around the world.A complete earthquake early warning system includes the identification of the earthquake location, estimation of its magnitude, estimation of its intensity at a target zone, and the dissemination of relevant information.The rapid determination of the earthquake magnitude is the most important part of such a system, after determining the location of the earthquake, because its accuracy affects predictions of ground motion of a target area and has influence on the issuance of warnings.An earthquake early warning system should provide the longest emergency response time possible.Full use must be made of the limited information from seismic stations nearest to the epicenter when calculating the earthquake magnitude, using special algorithms to extract the parameters that can better reflect the characteristics of earthquake magnitude from few data.Therefore, it is necessary to develop some method to calculate earthquake magnitude that is non-traditional, stable, and reliable.In this study, we used a simple function of the form Bt·exp(-At) and determined A and B in terms of the least-squares method by fitting this function with a 2-s time window of the first-arrival P waveform envelope.We proposed three methods for drawing waveform envelopes, which we then compared and analyzed using actual seismic records.An optimal method of drawing the envelopes was achieved, improving the method using the waveform envelope to obtain the magnitude.Based on 225 vertical recordings from the sensors of the Shandong Seismic Network, whose distances of separation are < 100 km and that have an SNR ≥ 3 after processing and statistics, we obtained a statistical relationship with magnitude, envelope parameter B, and the maximum speed for the 2-s time window of the first-arrival P waveform.An inspection of the results shows that the difference between this and the actual magnitude is small (0.36).According to a computational analysis of the Shandong Seismic Network data, we found a good linear relationship between lgB and epicentral distance Δ, regardless of the magnitude.Therefore, we can quickly estimate the magnitude of an earthquake using empirical formulas with the maximum amplitude of the 2-s P waveform and parameter B, effectively increasing the warning time and greatly reducing the warning blind spot.The fitting formula used to estimate the magnitude in this study has lower error and higher accuracy compared with the existing empirical formula when estimating earthquake magnitude in the Shandong region.However, because of the lack of seismic data for earthquakes > M5, the inversion formula has some limitations, and in addition, parameter B has strong regional characteristics.This study is based on the Rushan earthquake in the Shandong region, for which the statistical relationship between magnitude, envelope parameter B, and the maximum speed for the 2-s time window of the first-arrival P waveform was based.Therefore, the empirical relationship could be applied to the Jiaodong Peninsula that has similar geological structural characteristics.When an earthquake next occurs in the Jiaodong Peninsula, we will be able to obtain parameter B quickly using the data for the 2-s time window of the first-arrival P waveform at the station nearest to the epicenter.From this, it will be possible to estimate the earthquake magnitude simply and quickly, and effectively increase the warning time, which will greatly reduce the warning blind spot.
