Abstract: A method of using oriented seismic sensors to delineate the surface of a geologic unit having an anomalous velocity, such as salt dome is disclosed. Seismic sensors having three orthogonal axes of sensitivity are sealed in a housing and are attached to the outside of a tubing means. The tubing means is lowered into a wellbore that penetrates the geologic unit to a known depth, and a liquid such as cement is pumped through the tubing and up the annular space to fixedly attach the sensors to the geologic formation. The orientation of the sensor axes can then be calculated from an observed orientation of the reference directions of the sensor housings. Seismic wavefields are then propagated through the geologic unit and the surrounding earth, and are observed by the sensor axes of sensitivity, and are recorded and transmitted to the top of the tubing.

Abstract: A method for using mode converted P- or S- wave data to delineate the surface of an anomalous geologic structure such as a salt dome is disclosed. Seismic wavefields are propagated from near the surface, through the earth, and through the anomalous geologic unit, so that a wavefield encounters the geologic unit at a non-normal incidence angle to generate a converted S- wave. Incidence angles of the direct arrival and converted waves are then determined. The intersection point of each converted S- wave raypath with each direct arrival raypath is determined, to provide a length of the raypaths. Travel times along the raypaths are determined, and a point on the interface of the anomalous geologic unit with the surrounding earth is determined by comparing raypath travel time differences with the recorded arrival time differences.