Geophysics has been an integral part of the Waste Isolation Pilot Plant since its inception. Previous activities have included electrical resistivity surveys, review of petroleum exploration seismic lines, purchase of aeromagnetic and gravity surveys, installation of an earthquake seismometer, a seismic refraction survey, and five seismic reflection surveys. Ongoing or planned activities include installation of a multistation seismometer array, subsurface radar, vertical-gradient aeromagnetics, and high-resolution seismic work.

The seismic reflection and gravity data indicate complex structure in the northern part of the site. The seismic lines show a deterioration in reflector quality, character, and continuity within this disturbed zone. Events within the Castile Formation have a blocky nature with abrupt offsets and angular discontinuities between blocks. The lower members of the Castile Formation are thinner than normal. Both the underlying Delaware Mountain Group and overlying Salado Formation are less deformed than the Castile. Well control is consistent with the seismic interpretation. An interesting feature is an "expandable scale" contraction of the lower Salado in two wells in which individual beds are present but have been reduced 10 to 50% in thickness.

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