Determination of High-frequency Rayleigh Wave Phase Velocity from ESAC Method: a Real-world Example in Karamay

摘要

Spatial auto-correlation (SPAC) method has been widely used in extracting surface wave phase velocities from ambient seismic noise.In this method,the relation between SPAC coefficients and zero-order Bessel function of the first kind is utilized and surface wave phase velocities is obtained by inverting the observed SPAC coefficients.Classic SPAC method requires a receiver at the center and the other receivers are uniformly distributed along the circumference.Extended spatial auto-correlation (ESAC) method is recognized as an extended version of classic SPAC methods and allows the receivers to be arbitrary distribution,which greatly enlarges the application scope of SPAC method.In SPAC community,when SPAC coefficients are being estimated,time-averaged cross-spectra and power-spectra are firstly calculated,then the SPAC coefficients are computed by normalizing the cross-spectra with power-spectra.Recently,however,some researchers calculated the SPAC coefficients at each time window first,then averaged all the windows to get final SPAC coefficients (called the 'whitened complex coherency').The practical part of whitened complex coherency has no relation with standard zero-order Bessel function of the first kind.It is a scaled version of Bessel function.Although the whitened complex coherency has been applied successfully in low frequency band (＜ 2Hz),it requires further verification for application in high frequency band (≥ 2Hz).In this paper,ESAC method is used to determine Rayleigh wave phase velocity for a real-world example in Karamay.Data processing steps of ESAC method is described in the first place,and then,one set of ambient seismic data records is utilized in Karamay and we extract surface wave phase velocities at frequency band of 1.5-5Hz.The results show that the ESAC method is able to retrieve high-frequency band surface wave phase velocities.