Research On Key Technologies Of 3D Seismic SH-wave Exploration

In shallow engineering survey,seismic exploration method is a common geophysical method.It has been applied much more widely to large-scale engineering site investigation,structural detection,cavity detection,high speed rail way and high way subgrade investigation,tunnel surrounding rock classification,and geological prediction.In these engineering survey,sometimes it is not the best choice,because some basic challenges are faced,such as:(1)engineering survey is a small scale and subtle investigation,the inhomogeneity of near-surface media are relatively significant,and in special,those rich scattering and incontinuous reflection events of seismic wave result from miscellaneous fill and stone filling.(2)the mixture of body wave and Rayleigh surface wave resulted from depth limit of target layers leads to difficulty of separation and identification in seismic processing.(3)emergence angle of reflected seismic wave in shallow engineering survey is much greater than in petroleum exploration,because different target depth,in which the emergence angle is almost zero,making received seismic signals in Z-component be not only P-waves,but also contain much more converted SV waves from subsurface layers.We know it is difficult to separate them from mixture records of P-wave and converted wave.(4)for size of target in engineering survey,the larger wavelength of seismic P-wave results in low resolution.These reseasons mentiond above make the near-surface P-wave seismic data have worse imaging so that seismic method is an alternative choice in engineering survey,but unique choice in petroleum and coal exploration.Comparatively speaking,in engineering survey SH-wave has great advantages because it has low velocity,not easier to convert to other types of waves and higher resolution due to the shorter wavelength.It can solve those problems mentioned above.Specially,3D seismic is better than 2D seismic for solving some geological problems.So the author selects this 3D SH-wave seismic exploration as the PhD thesis.Through studying for 3 years and more,I focus on researches on the problems of source,acquisition and data processing of 3D SH-wave,and firstly suggest a 3D SH-wave exploration method and get some limited success.My research works,conclusions and innovation are as follows:(1)It is completely feasible to generate the SH-wave radiating to any direction in 360 degree through theoretical research and numerical simulation of wave equation with FDM.Numerical simulation of some different models and their corresponding polarization analysis prove the source loading mode can generate the pure shear wave and propagate to any direction in space.(2)A simple shear-rotation SH-wave source,can run rotation vibration and shear the ground surface,was made,and it can radiate SH-wave to any direction of 360 degree.Some acquisition showed that we could record the SH-wave in all of directions.(3)By theoretical analysis,an algorithm to rotate 2 components of SH-wave signal to a component I designed makes the data processing easy as 3D P-wave processing.In processing seismic modelling data and real data,it is proved that is effective.(4)In a case of subway tunnel survey,3D SH-wave is used to investigate the boulder by using our simple SH-wave source and 3D SH-wave processing.It is better to measure the boulders for improving the engineering progress and reducing the risk of building process with tunnel boring machine(TBM).I think I have solved the main key problems of 3D SH-wave survey from source,acquisition to processing as a new exploration technology.At present,3D SH-wave has applied in the real exploration test.I believe that we have to need a vibroseis source for a large scale of application of 3D SH-wave survey in near future.Fathur research on theory and practice of 3D SH-wave will be must.This thesis includes 6 chapters.The first one is introduction of thesis about research objectives and research method and innovation.The second chapter states the theory of SH-wave,and the third chapter discusses the numerical simulation of 3D SH-wave excitation and propagation.In chapter 4,it depicts the source of SH-wave design and acquisition.In chapter 5,the processing of 3D SH-wave data and tests of real data processing are stated.Last chapter,chapter 6 summarizes main works and conclusions.