Laboratory measurements and field data indicate that self‐potential anomalies comparable to those observed in many areas of geothermal activity may be generated by thermoelectric or electrokinetic coupling processes. A study using an analytical technique based on concepts of irreversible thermodynamics indicates that, for a simple spherical source model, potentials generated by electrokinetic coupling may be of greater amplitude than those developed by thermoelectric coupling. Before more quantitative interpretations of potentials generated by geothermal activity can be made, analytical solutions for more realistic geometries must be developed, and values of in‐situ coupling coefficients must be obtained. If the measuring electrodes are not watered, and if telluric currents and changes in electrode polarization are monitored and corrections made for their effects, most self‐potential measurements are reproducible within about ±5 mV. Reproducible short‐wavelength geologic noise of as much as ±10 mV, primarily caused by variation in soil properties, is common in arid areas, with lower values in areas of uniform, moist soil. Because self‐potential variations may be produced by conductive mineral deposits, stray currents from cultural activity, and changes in geologic or geochemical conditions, self‐potential data must be analyzed carefully before a geothermal origin is assigned to observed anomalies. Self‐potential surveys conducted in a variety of geothermal areas show anomalies ranging from about 50 mV to over 2 V in amplitude over distances of about 100 m to 10 km. The polarity and waveform of the observed anomalies vary, with positive, negative, bipolar, and multipolar anomalies having been reported from different areas. Steep potential gradients often are seen over faults which are thought to act as conduits for thermal fluids. In some areas, anomalies several kilometers wide correlate with regions of known elevated thermal gradient or heat flow.

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A model has been developed to relate the velocities of acoustic waves Vp and Vs in unconsolidated permafrost to the porosity and extent of freezing of the interstitial water. The permafrost is idealized as an assemblage of spherical quartz grains embedded in a matrix composed of spherical inclusions of water in ice. The wave‐scattering theory of Kuster and Toksoz is used to determine the effective elastic moduli, and hence the acoustic velocities. The model predicts Vp and Vs to be decreasing functions of both the porosity and the water‐to‐ice ratio. The theory has been applied to laboratory measurements of Vp and Vs in 31 permafrost samples from the North American Arctic. Although no direct measurements were made of the extent of freezing in these samples, the data are consistent with the predictions of the model. Electrical resistivity measurements on the permafrost samples have demonstrated their essentially resistive behaviour. The ratio of resistivity of permafrost in its frozen state to that in its unfrozen state has been related to the extent of freezing in the samples. Electromagnetic and seismic reflection surveys can be used together in areas of permafrost: firstly an EM survey to determine the extent of freezing and then the acoustic velocity model to predict the velocities in the permafrost. The necessary transit time corrections can thus be made on seismic reflection records to compensate for the presence of permafrost.

Self‐potential (SP) data from the Cerro Prieto geothermal field in Baja California, Mexico have been inverted using a model consisting of a vertical contact separating regions of different electrical properties. A temperature source is assumed to coincide with the vertical contact between materials with different thermoelectric coupling coefficients. A derivative‐free Levenberg‐Marquardt algorithm is used to estimate values for the depth, vertical extent, length, and intensity of the source region. The depth to the top of the source is estimated to be about 1.3 ± 0.2 km, which agrees quite well with the depth to the top of the production zone determined from drilling. The vertical extent and length of the source region are estimated to be 11 ± 3 km and 9.9 ± 0.4 km, respectively. There appears to be geologic evidence for the presence of a fault or fault zone within the geothermal field that roughly coincides in location with the self‐potential source region. The conductivity on the east side of the production zone is estimated to be 80 percent of the value to the west, which is in general agreement with field resistivity measurements. Thermoelectric coupling coefficients measured in the laboratory on samples of reservoir rock are not large enough to explain the −340 ± 40 mV source intensity predicted by the model, possibly because the laboratory measurements were made at temperatures about 300°C lower than the reservoir value. These results do not rule out the possibility of a streaming potential source mechanism.