Gaussian beam migration (GBM) is an effective
and robust depth seismic imaging method, which
overcomes the disadvantage of Kirchhoff migration in
imaging multiple arrivals and has no steep-dip limitation of
one-way wave equation migration. However, its imaging
quality depends on the initial beam parameters, which can
make the beam width increase and wave-front spread with
the propagation of the central ray, resulting in poor
migration accuracy at depth, especially for exploration
areas with complex geological structures. To address this
problem, we present an adaptive focused beam method for
shot-domain prestack depth migration. Using the information
of the input smooth velocity field, we first derive an
adaptive focused parameter, which makes a seismic beam
focused along the whole central ray to enhance the wavefield
construction accuracy in both the shallow and deep
regions. Then we introduce this parameter into the GBM,
which not only improves imaging quality of deep reflectors
but also makes the shallow small-scale geological structures
well-defined. As well, using the amplitude-preserved
extrapolation operator and deconvolution imaging condition,
the concept of amplitude-preserved imaging has been
included in our method. Typical numerical examples and
the field data processing results demonstrate the validity
and adaptability of our method.