Geophysical investigations were conducted at the proposed Maricopa SSC site in support of the geotechnical program for the State of Arizona site proposal. Modeling of a gravity survey across Rainbow Valley showed that the minimum depth to bedrock in the center of this basin is 750 meters (2500 feet). Gravity and magnetic surveys in Maricopa Valley between the north and south Maricopa Mountains indicated the possible presence of faults and diabase dikes. Seismic refraction surveys in the area of the proposed Injector Ring complex indicated a buried bedrock ridge about 400 meters (1300 feet) wide and approximately 25 meters (80 feet) below the surface. Geophysical surveys were also conducted at the Twin Buttes Mine near the proposed Sierrita SSC site. These surveys included gravity, seismic refraction, seismic reflection, DC resistivity and IP, and CSAMT surveys. Since the geology and geotechnical properties at the Twin Buttes mine are very well documented from extensive drilling, these surveys provide a calibration of observed geophysical signatures over various rock types.

Geophysical surveys were conducted in the Pima mining district by students from the University of Arizona. The surveys were concentrated along section B-B' from Cooper (1973). The objectives of this survey included: teaching geophysical techniques, mapping regional structure along this profile, and determining which geophysical techniques were most useful for regional .mapping in this area. Controlled source audio-frequency magnetotelluric (CSAMT) surveys successfully mapped depth to basement along this profile. Seismic refraction surveys were not able to map depth to basement. Either the depth to basement was beyond the range of the arrays used in this experiment or there is insufficient contrast in the velocity between the basement and the overlying rocks. A test of the seismic reflection method was carried out using a walk-away noise spread. Possible reflections from basement were noted but were not sufficiently diagnostic to be routinely use able.

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Tucson Electric Power (TEP) is carrying out subsurface investigations in order to locate more groundwater for cooling at the Sundt power-generating plant. To assist with this investigation, the University of Arizona GEN/GEOS 416/516 Field Studies in Geophysics class conducted geophysics surveys in an area just south of Davis-Monthan Air Force Base and between UTM coordinates 508,555 to 511,753 East and 3,553,705 to 3,556,895 North. Four geophysics methods (Gravity, Magnetics, Transient Electromagnetics (TEM), and Passive Seismic) were employed to locate a postulated fault, which may be correlated with ground water flow. A broad regional magnetic anomaly was mapped, as the magnetic field decreases steadily from NE to SW. There are no significant magnetic field anomalies that could be related to a potential fault. The Gravity results show a regional gravitational gradient, steadily decreasing from NE to SW, with a large isolated anomaly apparent around 1500m from the base station at the NE corner of the survey area. But, this large anomaly is a localized, and does not appear on the adjacent parallel survey lines, therefore it is not related to a potential fault contact. The Passive Seismic survey detected a deep boundary at 100m to 160m in elevation, but the depths interpreted from the 11 stations are scattered and do not show a clear trend. The Transient Electromagnetic (TEM) data show a consistent difference in depth to a low-resistivity layer along the profile line. The four TEM stations north of Interstate 10 (I10) have an average elevation for the 10 Ohm-m contour line of 720 meters. The four TEM stations south of I10 have an average elevation for the 10 Ohm-m contour line of 670 meters. This offset may be related to the postulated fault.

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