Inverse-Ray Imaging of a 3D Homogeneous Layer Based on Common-Shot Gathers of Oblique Profiles
王天楷(Tan-Kin Wang)；張凱銘(Kai-Ming Chang)
Apparent dip ； Migration ； Multi-channel seismic ； Ray geometry ； Reflector ； Travel time
Terrestrial, Atmospheric and Oceanic Sciences
|Volume or Term/Year and Month of Publication||
16卷3期（2005 / 08 / 01）
547 - 561
Imaging of 3D structural interfaces through reflected rays shooting from common-shot gathers is presented in this paper. First, by fitting the reflected arrivals picked from common-shot gathers, we calculate apparent clips and the shortest distances between sources and reflectors along two profiles. Then, based on the geometry of the profiles and a planar reflector, a unit normal vector of the reflector is determined from the apparent clips and the azimuths of two oblique profiles. A special case, when apparent clips are zero along two parallel profiles, for determining the reflector normal is also investigated. We propose three criteria to ensure the selected travel-times along two profiles resulting from the same planar reflector. These are that firstly, the same shortest distance from sources to the reflector is utilized; and secondly, we want to ensure the same normal of the reflector, and finally, the same ray distance. Prestack inverse-rays developed in this paper are applied to image the bathymetry of the Hoping Basin in the southernmost Ryukyu subduction zone and the fourth layer of the SEG/EAEG over-thrust model. Based on common-shot gathers along seven oblique profiles in the Hoping Basin, most of the reflection points are well imaged through inverse rays except when variation of the interface depth exceeds 300m across profiles with spacing greater than about 20km. Inverse-ray imaging of the over-thrust model also provides good agreement to its fourth interface except that imaging errors of about 1km in depth are found near the thrust faults. Inverse-ray imaging of 3D structures from 2D multi-channel seismic profiles is demonstrated if a pseudo-3D structure (a planar reflector) exists between profiles or if at least two profiles are within a Fresnel zone. Although this technique deals with a single-layered problem currently, it is fundamentally important when we extend it to image inhomogeneous multilayered media.