Numerical modelling and propagation law of seismic wave field in loess plateau of Ordos basin
In order to study the propagation law of seismic waves and the generation mechanism of noise in the loess plateau,this paper establishes 3D realistic models(velocity and quality factor Q)of the loess plateau in Or-dos basin according to actual surface elevation and velocity structure of the Qingcheng North 3D work area.Then under the condition of undulating land surface,3D numerical modelling using the coordinate transforma-tion method is accomplished based on a viscoacoustic wave equation with explicitly expressed quality factor.This method can simulate the strong energy noise near the offset caused by complex near surface and strong at-tenuation effects,and obtain simulation results similar to the real seismic data.Through wave field analysis of the numerical modelling results of the models with different complexity,this paper gradually clarifies the genera-tion mechanism of near-offset strong energy noise,multiple reflection and multiple refraction.Finally,this paper analyzes the differences in wave field characteristics at different locations(plateau,ridge,hillside,ditch)and at different source depth in the loess plateau area based on the numerical modelling and actual data.Analysis shows that when excited in the ditch,the near-offset strong energy noise is weaker,and the data quality is rela-tively good;As the source depth increases,the high-frequency component of the signal gradually increases;For real seismic data acquiring in the loess plateau,it is necessary to avoid excitation in the dry loess layer and try to excite in the clay layer or deeper layer.The conclusion of wave field analysis has positive guiding significance for real data acquiring and processing in the loess plateau.
loess plateau3D viscoacoustic equationnumerical modellingquality factorwave propagation law
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