Subsalt velocity model building

A subsurface velocity model, comprising:

• one or more velocity values in a salt body;
• one or more velocity values in a top salt sedimentary area disposed above the salt body;
• and
• one or more velocity values in a subsalt sedimentary area disposed below the salt body, wherein the one or more velocity values in the subsalt sedimentary area comprises one or more velocity values in a subsalt layer disposed directly below the salt body.

A computer-readable medium having stored thereon computer-executable instructions which, when executed by a computer, cause the computer to:

• determine a velocity of a sedimentary area surrounding a salt body;
• select a top horizon of the salt body;
• perform a salt-flood migration on a subsurface velocity model containing the salt body, the sedimentary area and a subsalt sedimentary area disposed below the salt body;
• select a base horizon of the salt body;
• determine an initial velocity of the subsalt sedimentary area by interpolating the velocity of the surrounding sedimentary area with one or more boundaries defining the salt body;
• and
• update the initial velocity of the subsalt sedimentary area.