Traveltime Analysis of VSP Seismograms in a Horizontal Transversely Isotropic Medium: A Physical Modeling Result

VSP震波訊號於水平橫向非均向性介質的走時分析：物理模型結果

張永孚(Young-Fo Chang) ； 張智雄(Chih-Hsiung Chang)

《Terrestrial, Atmospheric and Oceanic Sciences》 12卷4期 (2001/12) Pp. 685-693

並列摘要

In order to investigate the effects of anisotropy in a VSP survey, the multi-component VSP data for observing the qP-, qSH- and qSV-waves were collected with two different source-to-well offsets in an elastic transversely isotropic medium (TIM) with a horizontal symmetry axis (HTI). The traveltimes of the events were then computed using two different algorithms: first with elastic constants of the medium, and second with “isotropic velocities”. Comparing the traveltimes of computations with the recorded data, a very clear and important consequence can be derived. For strongly anisotropic media (the anisotropy for the qP- and qS-waves are 25% and 29%, respectively, in our laboratory work), the effects of anisotropy increase with increasing source-to-well offset. As the source-to-well offset is small compared with the depth of the receiver (offset/depth ≦ 0.2 in our work), the effects of anisotropy can be ignored. However, in processing a large source-to-well offset VSP survey (offset/depth ≧0.35 in this study), special attention must be paid on the effects of anisotropy.

並列關鍵字

Anisotropy ； Vertical seismic profile ； Physical modeling