A seismic tool assembly for effecting a drill hole and enlarging a lowermost end thereof whereby an anchor can be set more securely therein. A drill bit is inserted through an opening in a drill stop member, which is mounted on a stabilizer mounted within at least a portion of the drill hole. The bit is then inserted through each of the drill stop member and the stabilizer to attain a drilling position. The lower end of the bit has a cutting portion having a cutting radius greater than that of the bit body whereby, when the bit is inserted fully into a lowermost end of the hole and rotated, the cutting portion enlarges the lowermost end, whereby flanged portions of an anchor will rest within the enlarged area, retaining the anchor in place.