The application of 3-D ESMODEL in loess plateau of western China

Summary In Ordos basin in western China, the surface is covered by exceedingly thick loess, surface elevation varies acutely, and there are poignant lateral variations in thickness of weathering layer. The lateral weathering layer velocity is relatively stable; however, the vertical weathering layer velocity varies continuously with depth. So, there are many difficulties in near-surface survey, model-building of nearsurface structures and solving the uncertain problem of static correction. The conventional tomostatics methods may fail to solve the serious statics problem because of high dependence on initial near-surface model. A new tomostatics method named ESMODEL method has been developed by Chen. We applied the ESMODEL method to solve the statics problem for the land data acquired in experimental area of Ordos basin in western China. The ESMODEL method uses the conjugate-gradient algorithm in conjunction with the genetic algorithm to inverse the parameters of near-surface model from picked first-break time and estimates the statics, it is less dependent on the initial near-surface model. The stacked section after the ESMODEL static correction is significantly improved in comparison with that after conventional tomostatics correction. Then, the residual reflection statics are calculated using the Monte Carlo resident statics method to further improve the data quality.