Abstract: A method for producing an inverse vertical seismic profile using a seismic source place down a borehole has been invented. The directly transmitted waves from the seismic source and the secondary reflectances thereof are detected by a sensor(s) on the earth's surface. The method depends only on knowing the relative arrival times at the sensor of the direct waves and the secondary reflectance waves.

Abstract: The specification discloses a method and system for determining the position of a drill bit in the earth without interrupting the drilling operations. In operation, rotation of the drill bit against the formation being drilled generates coherent acoustical signals which are recorded at the surface of the earth by a plurality of spaced detectors. The signals recorded at each of the different detectors are time shifted relative to each other. These time shifts correspond to possible locations of the drill bit within the earth and are controlled to some degree by the length of drill pipe in the borehole. After the acoustic signals are shifted in time their coherency is determined. This procedure is repeated for a number of assumed locations of the drill bit. The drill bit position is determined to be at the location having the highest coherency value.