A quadripole resistivity survey of the Imperial Valley, California

A quadripole resistivity survey of the Imperial Valley, California was carried out from the Salton Sea in the north to the Mexican border in the south. The east and west boundaries of the survey were the topographic limits of the valley. The quadripole resistivity method consists of sequentially energizing two orthogonal bipole sources with a square wave of electric current and measuring the resultant electric fields with a pair of orthogonal wire receivers. Two resultant electric fields are measured and by combining them in different proportions, their resultant can be made to rotate through 360 degrees. By performing this procedure, an ellipse of resistivity can be calculated at each measurement location. The arithmetic mean of the maximum and minimum axes of the ellipse is a tensor invariant resistivity. It was this value which was used to define the variation of electrical resistivity over the Imperial Valley. The quadripole survey of the Imperial Valley was undertaken to compare its known geothermal fields with previously unsurveyed areas. The results show that the geothermal fields of the Imperial Valley have distinctive resistivity characteristics. A large circular area south of the city of Brawley was found which has the same characteristics as the known geothermal fields. From the resistivity data, it is predicted that this south Brawley resistivity anomaly represents a geothermal field which will produce water with a temperature of approximately 200°C and with a salinity between 20,000 and 50,000 ppm. A well to test the prospect was scheduled to be drilled early in 1978. © 1978 Society of Exploration Geophysicists.