Statistical Study On Spatial Coherence Function Of Seismic Surface Wave

The site conditions have an impact on the propagation of seismic waves and the spatial coherency of ground motions.Usually,people mainly pay attention to the spatial coherency of the soil layer site,and the strong earthquake records obtained in the soil layer site generally include P waves,S waves,surface waves and various reflected coda waves(coda waves).The surface waves in seismic records account for a large part especially in basins.For the research on coherency function,the S-wave time window is often selected for statistical analysis,and the entire earthquake record is used by a small group of people for calculations,however,the coherency function model parameters obtained from different seismic wave types are quite different.Because of few strong earthquake records in basin arrays and it is difficult to completely separate surface waves from seismic waves,there are few studies on the coherency of surface waves.In order to meet the application of seismic analysis of various site types and various engineering structures,the surface waves are discussed in this paper for coherency research.The main research results and contents are as follows:1.The acceleration records of the Event-7 and Event-8 earthquakes of the Taiwan LSST array and the Event-40 earthquake of the SMART-1 array were selected,and the P wave?S wave and surface wave were separated from the seismic waveforms to calculate energy ratio.The result shows: the energy ratio of S wave is the largest,surface wave takes the second place,and P wave is the smallest.2.The surface wave coherency functions which use the Loh coherency function model to fit the 12 different distances with the station spacing in the range of 6m-800 m are Calculated.The surface wave coherency function fitting parameters which can be used as a large basin in the seismic analysis of long and large structures are given finally,which can be used as a reference for the synthetic ground motion field.3.The coherency coefficients of surface waves and S waves were Compared and analyzed in the last,the conclusion is: when the distance (9 < 50 m,the coherency coefficients of the surface wave and S wave are basically the same;when the distance(9 > 50 m,the coherency coefficient of the surface wave is smaller than the S-wave,and the difference between the two gradually increases as the distance increases;when the distance (9 > 500 m,the spatial coherency of the surface wave hardly exists,and no further consideration is needed.