Exploring a subsurface formation

1 . A method of mapping a subsurface formation, the method comprising:

generating a velocity model representing the subsurface formation based on the seismic data;

determining an upper bound for traveltime within the velocity model from a seismic source by:

converting the velocity model into a slowness model;

integrating slowness along straight paths from the seismic source to boundary points of the slowness model to generate traveltime values;

determining an upper bound of traveltime for seismic rays traveling within the velocity model by selecting a maximum traveltime value from the straight paths; and

generating a seismic image of the subsurface formation by migrating the seismic data using Kirchhoff depth migration, where traveltime is calculated through ray tracing, and the maximum traveltime determines the stopping point for ray tracing.

2 . The method of claim 1 , further comprising updating the velocity model.

3 . The method of claim 2 , wherein updating the velocity model comprises:

generating estimated traveltime fields using the upper bound of traveltime for seismic rays traveling within the velocity model;

generating picked traveltime fields based on the seismic data; and

generating a tomographic kernel based on differences between the estimated traveltime fields and the picked traveltime fields.

4 . The method of claim 3 , wherein velocity updates based on the tomographic kernel are incorporated into the velocity model.

5 . The method of claim 4 , wherein migrating the seismic data comprises performing Kirchhoff migration on the seismic data.

6 . The method of claim 5 , further comprising conducting a seismic survey of the subsurface formation to generate seismic data.

7 . The method of claim 6 , further comprising performing field activities based on the seismic image of the subsurface formation.