Exploration of Subsurface Structures: Reflection Seismic Method and VSP (Vertical Seismic Profiling)

Abstract

Seismic reflection method is useful to explore deep subsurface structures in details, not only for prospecting of oil but also for engineering seismology. As a wide band of frequency from several tens of Hz to 0.1Hz is required for precise prediction and simulation of strong motions in latest studies, the subsurface structures are necessary to explore, up to the seismic basement whose velocity is around 3km/s for S wave or over 5km/s for P wave. Recently, some seismic reflection surveys of this kind have been done in the vicinity of large cities, such as Tokyo and Osaka. However, althogh the velocity structures are very important for the simulation of strong motions, the velocity analyses based on reflection data are usually used to optimize the stacking quality of CDP (Common Depth Point) data and the geological structures are mainly discussed in the processed seismic sections.
Therefore, in this paper, the author will review the CDP stacking method of reflection data, examining the principles of velocity analysis in simple and complex structures, and Vertical Seismic Profiling (VSP) as a good tool to calibrate the seismic reflection data.