Study On The Characteristics And Suppression Methods Of Surface Waves In Non-ideal Conditions

Surface wave is a regular noise wave existing widely in seismic data. It can be defined as a group of events that contaminates seismic data by forming a high dip (low velocity) and high amplitude cone, which can dominate near-surface events on the seismic records, and it is normally found in land seismic surveys. However, it is the pivotal question in how to remove or pick-up this kind of noise in seismic data. In order to find a better way to suppress surface wave, the characteristics under non-ideal conditions must be researched.Rayleigh wave is sort of sub-wave, which is low-frequency, low-speed, propagates along the surface of the earth, and its amplitude is only significant down to the depth of a few wave lengths. Below that depth, the displacement is negligible. In this paper,the basic theory and wave equation are studied, then the propagation features , overlying air (liquid) , unconsolidated overburden,in the constant gradient velocity and viscoelastic medium, are discussed. Including the relations between Rayleigh wave propagation velocity and the geophysical parameters, such as Poisson's ratio, quality factors, S-wave velocity. Their dispersion equations are derived and the models are established, depending on the propagation features under viscoelastic medium. The suppression methods are verified effective and viable.After implementing a variety of methods ( such as S-transform,nonlinear filtering,frequency-wave number domain filter,one-dimension and two-dimension wavelet transforms decompose) to suppress surface wave, the advantages and disadvantages of those methods are summed up. Using the united methods to suppress surface waves, to overcome the disadvantages. In addition, a improvement F-K filter method velocity filtering method (frequency- apparent velocity filter) is proposed. Compared with the original methods, the above methods overcome the shortcomings and deficiencies to some extent. After those methods being used to suppress surface of the actual seismic data, the united methods (one-dimension and two-dimension wavelet transforms, f-k filter and two-dimension wavelet transforms) and frequency-apparent velocity filter are verified to be effective. The above methods can be directly used in the practical work. They have special value in seismic data processing.