Seismic Wavefield Simulation Applied To Test Performance Of EEW Software

With the completion of the National Seismic Intensity Rapid Reporting and Early Warning Project,China has renovated and built a total of 15,391 earthquake stations,covering four key areas in northern China,the north-south seismic zone,the southeast coast and the middle part of the Tianshan Mountains.The completion of the high-density earthquake monitoring networks also improves the timeliness and accuracy of the earthquake early warning system.However,most the regions doesn’t occur large earthquakes,which makes it impossible to test the reliability and stability of the earthquake early warning system.In addition,multi-source earthquakes generated by aftershock sequences of large earthquakes can lead to missed and false alarms in the early warning system.The purpose of this thesis is to address the problems of the Earthquake Early Warning system.The main works are as follows:(1)Collect 2442 strong ground motion data from 237 seismic events on Ki K-net and K-net and preprocess these waveform data and intercepted the waveform data using energy duration.It is found that the 99% energy duration not only reduces the simulation errors but also simplifies the subsequent operations by generating time records based on this energy duration.(2)For the methods of ground motion simulation,the applicability of various types of spectral expressions to this study is explained,the research idea of synthesizing the time course records based on the triangular series formula is determined,and the Fourier amplitude spectrum is used to describe the frequency domain characteristics of the simulated records.To meet the amplitude requirements of the time recordings of the rising and decaying phases of the ground shaking after the arrival of the P-wave,the gamma function is introduced as the intensity envelope function.Finally,three intensity envelope function model parameters and three Fourier amplitude spectrum model parameters are determined,and the corresponding waveform records can be generated by these model parameters.(3)The prediction equations of the model parameters are established by the leastsquares method,and the simulated records could be generated by the prediction equations.To verify the accuracy of the simulation results,three types of characteristic parameters are selected to compare the simulated records with the actual records.The results show that the overall characteristic parameters of the simulated records and the actual records meet the 1:1 ratio and are within 0.1～10 times of the measured results.(4)The simulated seismic events in Miyagi,Honshu East Coast offshore area,Yangbi and Menyuan are put into the early warning system for online simulation tests,and the results show that the errors of the actual and simulated records were all within 0.4magnitude units.Finally,a double-earthquake model is used to simulate a sequence of seismic events with a 1s interval between the seismic events in Sanming and Fuzhou.The test results of the early warning system are used to analyze the effects of multi-source earthquakes on the processing aspects of the earthquake warning system.