Variable Grid Finite-difference Seismic Modeling Of Irregular Topography

The leading edge of the seismic exploration is gradually transferred to the complexsurface areas, conventional processing and interpretation of the above complex irregulartopography is no longer applicable.In order to better address the exploration anddevelopment problems,we should study closely the media in the irregular topographyconditions seismic modeling,Under the irregular topography geological forward modelingcan be from the numerical simulation results,understanding,analysis of seismic wave fieldcharacteristics and seismic wave propagation law.thus summed up the characteristics tobetter guide seismic exploration.Under the irregular surface modeling is the key to deal with two issues:one is thereasonable selection of irregular topography elastic wave equation discretizationmethod;the other is the free boundary to realize the free boundary of surface zero stressboundary condition, adopting the optimization processing method.Departure from theabove two questions,first is the processing of the free boundary in the irregular topographyconditions,the vacuum method and generalized image combining the boundary,at theirregular topography is not directly deal with the normal stress,but direct sampling of theshear stress,and its efficiency improved to some extent;then is using elastic wave staggeredfinite difference discrete elastic wave equation,and also introduces a variable staggeredgrid to improve the efficiency of the irregular topography modeling,surface local gridencrypted,the surface local grid step smaller,while the relative global fine grid finitedifference significantly improve efficiency,save computer memory.High-orderstaggered grid finite difference simulation in the inner region, in order to meet freeboundary conditions at the boundary, we gradually reduce order simulation near theboundary.The simulation results show that:1.irregular topography give rise to the mutualconversion between the Rayleigh wave,body wave,will produce a scattering of P andscattering S and the scattering of surface waves.In addition,the ladder of the surfaceapproximation at eht surface will produce a “stepped burr”noise,the noise for the dramatic ups and downs of the model greatly affect the signal to noise ratio of seismic data.2.whenthe irregular topography function is relatively simple and underground strata is relativelyless complex,variable grid regardless of the shot record accuracy or saving time andmemory are preferred;surface complex underground complex,according to research need tooptimize methods.