Real-time Site Correction Method And Its Application In Earthquake Early Warning

The earthquake early warning system has extremely high requirements on the real-time processing of seismic data.The waveforms are not only from the seismic station installed in the bedrock,but also a large number of strong motion stations and seismic intensity meters stations which are installed in soil rather than bedrock.The amplification of the site cannot be ignored.In order to consider the site amplification effect in magnitude estimation and ground motion field prediction,it is necessary to correct the seismic waveforms under various site conditions in real time.A scalar is currently used to characterize the site amplification effect.Although this method is small in calculation,the frequency dependence of the site amplification factor is not fully considered.In order to balance the real-time requirements and the frequency correlation of the site amplification factor,this paper applies a real-time site correction method to earthquake early warning based on the records of some strong motion stations in Sichuan and Japan.The main contents are as follows:1.The strong motion stations of bedrock and non-basic rock sites in Sichuan area were selected to study the effect of real-time site correction method to predict ground motion under different working conditions.First calculate the site scalar,and the corresponding time domain filter is designed by using the reference site spectral ratio method.The ground motion of the target station is predicted from the record of the reference station using two site correction methods.By comparing the peak of ground motion acceleration(PGA)obtained by the two methods and the seismic intensity of the instrument,this paper finds that the time domain filter correction method can simulate the waveform of the target site in real time with a slightly higher accuracy.2.Select the ground motion record and borehole data of the IBRH18 strong motion station under the Class II site in Japan,the frequency response function of the site is calculated by the surface downhole spectral ratio method and the equivalent linearization method,then the corresponding filters are designed.The real-time site correction is performed on the surface ground motion record by using the filter.By comparing the actual ground motion in the borehole,we found that the accuracy of the spectral ratio method and the equivalent linearization method is better than that of the scalar correction method.The mean group delay spectrum method is used to estimate the time difference of seismic waves between surface and borehole.It is found that the site conditions have little influence on the phase of IBRH18 station used in this paper.At the same time,the IBRH10 strong motion station under the Class IV site was studied.It was found that the real-time correction method was not as effective as the IBRH18station at the IBRH10 station.3.For the IBRH18 strong motion station,the(?)、P_a、P_v andP_d were calculated from four types of seismic records(observed ground motion on surface,observed ground motion in the borehole,the borehole ground motion simulated by surface-borehole spectral ratio method and equivalent linearization method)respectively.It is found that the use of real-time site correction methods for the surface records can reduce the discreteness of the magnitude estimation parameters.