Traveltime calculations for qP, qSV, and qSH waves in 3D tilted
transversely isotropic media using fast sweeping method with a Newton
method local solver
Abstract
Efficient and accurate traveltime calculations of seismic waves have
important applications in tomography, prestack migration, earthquake
location, etc. Anisotropy significantly affects the traveltimes of
seismic wave. For high-resolution imaging and inversion, it is necessary
to consider anisotropy in the traveltime calculations. The fast sweeping
method (FSM) does not need to track and store the minimum traveltime
point of wavefront, which has important applications in computing the
anisotropic first-arrival traveltime. The conventional method that
solves a transformed traveltime quartic equation combined with FSM is
suitable for general anisotropic media. However, this method involves
finding the intervals of roots and solving the quartic equations using
bisection algorithm at each iteration, leading to high computational
cost and instability for the 3D problems. In our previous work, for the
vertical transversely isotropic (VTI) case, we developed an FSM to
compute the qP-wave first-arrival traveltimes by analytically solving
the simplified quadratic slowness equation in a specific
triangular-pyramid stencil. This method greatly improves the
computational efficiency. However, for the qP and qSV waves,
analytically solving the slowness equation cannot be extended to tilted
transversely isotropic (TTI) media. To address this problem, we
introduced the Newton method in the triangular-pyramid local solver to
quickly solve the TTI slowness equation. For the qSH wave, its slowness
equation is quadratic and simple to solve. The proposed method provides
an efficient procedure for the traveltime calculations of qP, qSV, and
qSH waves in 3D general TTI media. Numerical examples have verified the
efficiency and accuracy of the proposed method.