The Application Of The First Breaks Tomography Technique In The Seismic Exploration Of The Coal Field

The main geomorphological units in Western coal seismic exploration area are mainly desert, Gobi, mountains, loess plateau and so on, These complex geological conditions in the shallow surface results in serious absorption and attenuation to seismic wave. Consequently first break is not clear. The valid reflected signal is often"drowned" in the interference wave, so a high signal-to-noise ratio field data can not be obtained. It makes exploration project difficult to be fulfilled. Therefore, the first break wave tomography technology constrained with achievement of low velocity zone is significant, especially to high-speed layer excitation techniques for data acquisition and Datum Statics in data processing.First of all, basing on seismic wave propagation principles, the propagation rule and types of first wave in the surface model were analyzed. Then the basic principles of First-Break wave tomography technology were discussed.Using the first break of seismic direct wave, reverse branch, refraction wave and their combination , tomographic inversion was applied to obtain medium velocity underground. Then complex surface modeles can be established.Finally, to different surface types, actual examples were analysed and compared, including mountains, Gobi, desert, loess plateau region . Applying low speed investigation and first break tomographic inversion, the fine velocity model was established, Conducted by the velocity model, high quality raw data were obtained using high velocity layer excitation technique. Appling first break travel time tomography static correction, good continuity and high signal-to-noise ratio stacked section was generated. The well defined structural form and correspondence between layers provieded good foundation to improve the resolution in imaging process sequently. The seismic exploration result was apparent.