| Single station early warning is an important method of earthquake early warning.Combined with the current situation of scarcity of seismic stations in China,the construction of single station earthquake warning system for high-speed railway is an important method to reduce the earthquake threat of high-speed railway,and single station positioning is the key of single station early warning.In this paper,we will carry out relevant research,and hope to further improve the accuracy of the single station positioning method suitable for our country on the basis of previous work.The main research contents of this paper include: using the initial P-wave records of a single station to quickly determine the epicenter distance and azimuth,and then determine the longitude and latitude of the epicenter location.Finally,several strong earthquakes occurred in China are taken as examples to prove the effectiveness of the method.The thesis mainly completed the following work:1.B-Δ method and C-Δ method are introduced briefly.Based on 4716 strong motion records in China,empirical formulas suitable for B-Δ method and C-Δ method in China are obtained to obtain epicenter distance.The effects of time window length and filtering frequency on the two algorithms are studied respectively.The appropriate filtering frequency band and length of time window are found to reduce the error of the method.Finally,the calculation results of B-Δ and C-Δ methods are compared,and the conclusion is drawn.2.The calculation methods of epicenter azimuth are studied,including single value method(SV method),moving average method(MA method)and polarization analysis method(PCA method).The effects of fixed time window length(0.1-2seconds),data recording form,signal-to-noise ratio and filtering frequency band(mainly band-pass filter)on the three algorithms are studied.Secondly,the accuracy of various algorithms under the moving time window is studied.It is found that the accuracy of PCA method and SV method under moving time window is significantly improved.Through the analysis of moving time window,the method to improve the calculation of epicenter azimuth is further found.The SV method and PCA method are used to calculate the average value.Finally,it is found that when the difference between PCA method and SV method is less than 30°,there will be no abnormal data points,which can be used to determine the seismic azimuth of a single station.3.Three earthquakes with magnitudes greater than 6 in China(Wenchuan earthquake,Lushan earthquake and Kangding earthquake)are selected to verify the practicability of the algorithm. |
