Recent Applications of Turning-Ray Tomography And Tomostatics

By

 Xianhuai Zhu¹

(1) PGS Geophysical, 10550 Richmond Ave., Houston, TX

 Turning-ray tomography and tomostatics have been applied to areas with rugged topography and strongly variant near-surface geology. I review the methodology of turning-ray tomography and tomostatics, and show how the near-surface velocities estimated from turning-ray tomography are used for static correction, wave-equation datuming and prestack depth migration. Questions frequently asked will be highlighted to show 1) when and where tomostatics will work better than conventional refraction statics; 2) limitations of tomostatics; and 3) key steps to run tomostatics. Quality controls will be illustrated to ensure the robustness of turning-ray tomography and tomostatics.

Turning-ray tomography and tomostatics enhance interpretation and are applicable to areas where refraction statics often fail, such as thrust belts, high-velocity basalt or carbonate outcrops, unconsolidated low-velocity sand dunes, marine trenches and shallow gas cloud regions. Although it does not always provide better-stacked images than those from refraction statics, tomostatics are at least as good as refraction statics. Interpreters often find the near-surface velocity profile very useful when they determine a drill site.

Synthetic and field data examples have shown that the resolution of estimating a near-surface velocity model is directly dependent upon the picked first arrivals. Picking the first arrivals via a virtual reality system significantly improves the consistency of input data for the subsequent velocity estimation.