The Influence Of Smooth Processing Of Strong Earthquake Records On The Coherence Function

The coherence function |(?)jk| is often used to describe the spatial correlation of ground motion.According to the calculation formula of the coherence function,the theoretical value should be equal to 1 and independent of frequency.Therefore,in the actual calculation of the coherence function,the window function must be used to record strong earthquakes.The power spectrum and cross-power spectrum are smoothed,and the resulting coherence function0<|(?)jk|<1.There are many types of window functions.Different window functions and different bandwidths are used,which will have a certain influence on the calculation results of the coherence coefficients.This article has studied the above problems.The main work contents and analysis results obtained are as follows:1.The S-wave time window in the acceleration record of the 5th earthquake of Taiwan SMART-1 array was selected as analysis data.Respectively,the central station C00 and the inner ring stations 103,106,109,112,and the middle ring stations M03,M06,M09,M12,and the outer ring stations 003,006,009,012 respectively constitute different distances.Pairs of stations with d of 200m,1000m and 2000m.2.Using the Blackman window,Hamming window and Hanning window,as well as the different bandwidth of 0.68Hz,1.07Hz and 1.46Hz,the correlation coefficient between the three distances of 200m,1000m and 2000m is calculated respectively.3.Choosing the commonly used Loh model and Abrahamson model to fit the calculation results of the coherence coefficient.Through the comparison of the fitting curve,it is found that:The three window functions have little influence on the calculation result of the coherence coefficient,but the influence of the bandwidth is large.The larger the bandwidth,the smaller the coherence coefficient.Therefore,when calculating the coherence coefficient,it is necessary to select an appropriate bandwidth.