Kirchhoff diffraction mapping in media with large velocity contrasts

Finite‐difference methods for calculating traveltimes are superior to ray‐tracing methods in inhomogeneous media. However, when these techniques are applied to Kirchhoff migration, a severe problem occurs in the presence of large velocity contrasts. If finite‐difference traveltime methods are used to calculate first arrivals, an incomplete image is created because substantial subsurface information is often carried by direct body waves. We propose a solution to this problem by developing a new method of calculating later arrival times and applying both first and later arrival times to a Kirchhoff diffraction mapping algorithm. A comparison shows that the implementation of both first arrivals and later arrivals in Kirchhoff migration can substantially improve the images in media with large velocity contrasts.